merge ecc again

26 files changed, 1370 insertions, 279 deletions

diff --git a/Makefile.in b/Makefile.in
index fa88f61..a644719 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -27,7 +27,8 @@ COMMONOBJS=dbutil.o buffer.o \
 		signkey.o rsa.o random.o \
 		queue.o \
 		atomicio.o compat.o fake-rfc2553.o \
-		ltc_prng.o ecc.o ecdsa.o crypto_desc.o
+		ltc_prng.o ecc.o ecdsa.o crypto_desc.o \
+		gensignkey.o gendss.o genrsa.o
 
 SVROBJS=svr-kex.o svr-auth.o sshpty.o \
 		svr-authpasswd.o svr-authpubkey.o svr-authpubkeyoptions.o svr-session.o svr-service.o \
@@ -42,9 +43,9 @@ CLIOBJS=cli-main.o cli-auth.o cli-authpasswd.o cli-kex.o \
 CLISVROBJS=common-session.o packet.o common-algo.o common-kex.o \
 			common-channel.o common-chansession.o termcodes.o loginrec.o \
 			tcp-accept.o listener.o process-packet.o \
-			common-runopts.o circbuffer.o
+			common-runopts.o circbuffer.o curve25519-donna.o
 
-KEYOBJS=dropbearkey.o gendss.o genrsa.o
+KEYOBJS=dropbearkey.o
 
 CONVERTOBJS=dropbearconvert.o keyimport.o
 
diff --git a/algo.h b/algo.h
index dbbafd0..8cd4c9b 100644
--- a/algo.h
+++ b/algo.h
@@ -81,17 +81,27 @@ struct dropbear_hash {
 	const unsigned char hashsize;
 };
 
+enum dropbear_kex_mode {
+	DROPBEAR_KEX_NORMAL_DH,
+	DROPBEAR_KEX_ECDH,
+	DROPBEAR_KEX_CURVE25519,
+};
+
 struct dropbear_kex {
-	// "normal" DH KEX
+	enum dropbear_kex_mode mode;
+	
+	/* "normal" DH KEX */
 	const unsigned char *dh_p_bytes;
 	const int dh_p_len;
 
-	// elliptic curve DH KEX
+	/* elliptic curve DH KEX */
 #ifdef DROPBEAR_ECDH
 	const struct dropbear_ecc_curve *ecc_curve;
+#else
+	const void* dummy;
 #endif
 
-	// both
+	/* both */
 	const struct ltc_hash_descriptor *hash_desc;
 };
 
@@ -117,12 +127,6 @@ int check_user_algos(const char* user_algo_list, algo_type * algos,
 char * algolist_string(algo_type algos[]);
 #endif
 
-#ifdef DROPBEAR_ECDH
-#define IS_NORMAL_DH(algo) ((algo)->dh_p_bytes != NULL)
-#else
-#define IS_NORMAL_DH(algo) 1
-#endif
-
 enum {
 	DROPBEAR_COMP_NONE,
 	DROPBEAR_COMP_ZLIB,
diff --git a/bignum.c b/bignum.c
index e9810b3..4400969 100644
--- a/bignum.c
+++ b/bignum.c
@@ -78,8 +78,6 @@ void bytes_to_mp(mp_int *mp, const unsigned char* bytes, unsigned int len) {
 /* hash the ssh representation of the mp_int mp */
 void hash_process_mp(const struct ltc_hash_descriptor *hash_desc, 
 				hash_state *hs, mp_int *mp) {
-
-	int i;
 	buffer * buf;
 
 	buf = buf_new(512 + 20); /* max buffer is a 4096 bit key, 
diff --git a/cli-kex.c b/cli-kex.c
index 0cc730c..18285ac 100644
--- a/cli-kex.c
+++ b/cli-kex.c
@@ -47,27 +47,43 @@ void send_msg_kexdh_init() {
 
 	CHECKCLEARTOWRITE();
 	buf_putbyte(ses.writepayload, SSH_MSG_KEXDH_INIT);
-	if (IS_NORMAL_DH(ses.newkeys->algo_kex)) {
-		if (ses.newkeys->algo_kex != cli_ses.param_kex_algo
-			|| !cli_ses.dh_param) {
-			if (cli_ses.dh_param) {
-				free_kexdh_param(cli_ses.dh_param);
+	switch (ses.newkeys->algo_kex->mode) {
+		case DROPBEAR_KEX_NORMAL_DH:
+			if (ses.newkeys->algo_kex != cli_ses.param_kex_algo
+				|| !cli_ses.dh_param) {
+				if (cli_ses.dh_param) {
+					free_kexdh_param(cli_ses.dh_param);
+				}
+				cli_ses.dh_param = gen_kexdh_param();
 			}
-			cli_ses.dh_param = gen_kexdh_param();
-		}
-		buf_putmpint(ses.writepayload, &cli_ses.dh_param->pub);
-	} else {
+			buf_putmpint(ses.writepayload, &cli_ses.dh_param->pub);
+			break;
+		case DROPBEAR_KEX_ECDH:
 #ifdef DROPBEAR_ECDH
-		if (ses.newkeys->algo_kex != cli_ses.param_kex_algo
-			|| !cli_ses.ecdh_param) {
-			if (cli_ses.ecdh_param) {
-				free_kexecdh_param(cli_ses.ecdh_param);
+			if (ses.newkeys->algo_kex != cli_ses.param_kex_algo
+				|| !cli_ses.ecdh_param) {
+				if (cli_ses.ecdh_param) {
+					free_kexecdh_param(cli_ses.ecdh_param);
+				}
+				cli_ses.ecdh_param = gen_kexecdh_param();
 			}
-			cli_ses.ecdh_param = gen_kexecdh_param();
-		}
-		buf_put_ecc_raw_pubkey_string(ses.writepayload, &cli_ses.ecdh_param->key);
+			buf_put_ecc_raw_pubkey_string(ses.writepayload, &cli_ses.ecdh_param->key);
+#endif
+			break;
+#ifdef DROPBEAR_CURVE25519
+		case DROPBEAR_KEX_CURVE25519:
+			if (ses.newkeys->algo_kex != cli_ses.param_kex_algo
+				|| !cli_ses.curve25519_param) {
+				if (cli_ses.curve25519_param) {
+					free_kexcurve25519_param(cli_ses.curve25519_param);
+				}
+				cli_ses.curve25519_param = gen_kexcurve25519_param();
+			}
+			buf_putstring(ses.writepayload, cli_ses.curve25519_param->pub, CURVE25519_LEN);
 #endif
+			break;
 	}
+
 	cli_ses.param_kex_algo = ses.newkeys->algo_kex;
 	encrypt_packet();
 	ses.requirenext[0] = SSH_MSG_KEXDH_REPLY;
@@ -103,23 +119,38 @@ void recv_msg_kexdh_reply() {
 		dropbear_exit("Bad KEX packet");
 	}
 
-	if (IS_NORMAL_DH(ses.newkeys->algo_kex)) {
-		// Normal diffie-hellman
-		DEF_MP_INT(dh_f);
-		m_mp_init(&dh_f);
-		if (buf_getmpint(ses.payload, &dh_f) != DROPBEAR_SUCCESS) {
-			TRACE(("failed getting mpint"))
-			dropbear_exit("Bad KEX packet");
-		}
+	switch (ses.newkeys->algo_kex->mode) {
+		case DROPBEAR_KEX_NORMAL_DH:
+			{
+			DEF_MP_INT(dh_f);
+			m_mp_init(&dh_f);
+			if (buf_getmpint(ses.payload, &dh_f) != DROPBEAR_SUCCESS) {
+				TRACE(("failed getting mpint"))
+				dropbear_exit("Bad KEX packet");
+			}
 
-		kexdh_comb_key(cli_ses.dh_param, &dh_f, hostkey);
-		mp_clear(&dh_f);
-	} else {
+			kexdh_comb_key(cli_ses.dh_param, &dh_f, hostkey);
+			mp_clear(&dh_f);
+			}
+			break;
+		case DROPBEAR_KEX_ECDH:
 #ifdef DROPBEAR_ECDH
-		buffer *ecdh_qs = buf_getstringbuf(ses.payload);
-		kexecdh_comb_key(cli_ses.ecdh_param, ecdh_qs, hostkey);
-		buf_free(ecdh_qs);
+			{
+			buffer *ecdh_qs = buf_getstringbuf(ses.payload);
+			kexecdh_comb_key(cli_ses.ecdh_param, ecdh_qs, hostkey);
+			buf_free(ecdh_qs);
+			}
+#endif
+			break;
+#ifdef DROPBEAR_CURVE25519
+		case DROPBEAR_KEX_CURVE25519:
+			{
+			buffer *ecdh_qs = buf_getstringbuf(ses.payload);
+			kexcurve25519_comb_key(cli_ses.curve25519_param, ecdh_qs, hostkey);
+			buf_free(ecdh_qs);
+			}
 #endif
+			break;
 	}
 
 	if (cli_ses.dh_param) {
@@ -132,6 +163,12 @@ void recv_msg_kexdh_reply() {
 		cli_ses.ecdh_param = NULL;
 	}
 #endif
+#ifdef DROPBEAR_CURVE25519
+	if (cli_ses.curve25519_param) {
+		free_kexcurve25519_param(cli_ses.curve25519_param);
+		cli_ses.curve25519_param = NULL;
+	}
+#endif
 
 	cli_ses.param_kex_algo = NULL;
 	if (buf_verify(ses.payload, hostkey, ses.hash) != DROPBEAR_SUCCESS) {
@@ -147,7 +184,8 @@ void recv_msg_kexdh_reply() {
 	TRACE(("leave recv_msg_kexdh_init"))
 }
 
-static void ask_to_confirm(unsigned char* keyblob, unsigned int keybloblen) {
+static void ask_to_confirm(unsigned char* keyblob, unsigned int keybloblen,
+	const char* algoname) {
 
 	char* fp = NULL;
 	FILE *tty = NULL;
@@ -155,14 +193,16 @@ static void ask_to_confirm(unsigned char* keyblob, unsigned int keybloblen) {
 
 	fp = sign_key_fingerprint(keyblob, keybloblen);
 	if (cli_opts.always_accept_key) {
-		fprintf(stderr, "\nHost '%s' key accepted unconditionally.\n(fingerprint %s)\n",
+		fprintf(stderr, "\nHost '%s' key accepted unconditionally.\n(%s fingerprint %s)\n",
 				cli_opts.remotehost,
+				algoname,
 				fp);
 		m_free(fp);
 		return;
 	}
-	fprintf(stderr, "\nHost '%s' is not in the trusted hosts file.\n(fingerprint %s)\nDo you want to continue connecting? (y/n) ", 
+	fprintf(stderr, "\nHost '%s' is not in the trusted hosts file.\n(%s fingerprint %s)\nDo you want to continue connecting? (y/n) ", 
 			cli_opts.remotehost, 
+			algoname,
 			fp);
 	m_free(fp);
 
@@ -257,16 +297,17 @@ static void checkhostkey(unsigned char* keyblob, unsigned int keybloblen) {
 		return;
 	}
 
+	algoname = signkey_name_from_type(ses.newkeys->algo_hostkey, &algolen);
+
 	hostsfile = open_known_hosts_file(&readonly);
 	if (!hostsfile)	{
-		ask_to_confirm(keyblob, keybloblen);
+		ask_to_confirm(keyblob, keybloblen, algoname);
 		/* ask_to_confirm will exit upon failure */
 		return;
 	}
 	
 	line = buf_new(MAX_KNOWNHOSTS_LINE);
 	hostlen = strlen(cli_opts.remotehost);
-	algoname = signkey_name_from_type(ses.newkeys->algo_hostkey, &algolen);
 
 	do {
 		if (buf_getline(line, hostsfile) == DROPBEAR_FAILURE) {
@@ -319,17 +360,18 @@ static void checkhostkey(unsigned char* keyblob, unsigned int keybloblen) {
 
 		/* The keys didn't match. eep. Note that we're "leaking"
 		   the fingerprint strings here, but we're exiting anyway */
-		dropbear_exit("\n\nHost key mismatch for %s !\n"
+		dropbear_exit("\n\n%s host key mismatch for %s !\n"
 					"Fingerprint is %s\n"
 					"Expected %s\n"
 					"If you know that the host key is correct you can\nremove the bad entry from ~/.ssh/known_hosts", 
+					algoname,
 					cli_opts.remotehost,
 					sign_key_fingerprint(keyblob, keybloblen),
 					fingerprint ? fingerprint : "UNKNOWN");
 	} while (1); /* keep going 'til something happens */
 
 	/* Key doesn't exist yet */
-	ask_to_confirm(keyblob, keybloblen);
+	ask_to_confirm(keyblob, keybloblen, algoname);
 
 	/* If we get here, they said yes */
 
diff --git a/cli-runopts.c b/cli-runopts.c
index b8d304f..d20928b 100644
--- a/cli-runopts.c
+++ b/cli-runopts.c
@@ -450,7 +450,7 @@ void cli_getopts(int argc, char ** argv) {
 #ifdef ENABLE_CLI_PUBKEY_AUTH
 static void loadidentityfile(const char* filename) {
 	sign_key *key;
-	int keytype;
+	enum signkey_type keytype;
 
 	key = new_sign_key();
 	keytype = DROPBEAR_SIGNKEY_ANY;
diff --git a/common-algo.c b/common-algo.c
index 8076358..621a8cb 100644
--- a/common-algo.c
+++ b/common-algo.c
@@ -228,23 +228,32 @@ algo_type sshhostkey[] = {
 	{NULL, 0, NULL, 0, NULL}
 };
 
-static struct dropbear_kex kex_dh_group1 = {dh_p_1, DH_P_1_LEN, NULL, &sha1_desc };
-static struct dropbear_kex kex_dh_group14 = {dh_p_14, DH_P_14_LEN, NULL, &sha1_desc };
+static const struct dropbear_kex kex_dh_group1 = {DROPBEAR_KEX_NORMAL_DH, dh_p_1, DH_P_1_LEN, NULL, &sha1_desc };
+static const struct dropbear_kex kex_dh_group14 = {DROPBEAR_KEX_NORMAL_DH, dh_p_14, DH_P_14_LEN, NULL, &sha1_desc };
 
+/* These can't be const since dropbear_ecc_fill_dp() fills out
+ ecc_curve at runtime */
 #ifdef DROPBEAR_ECDH
 #ifdef DROPBEAR_ECC_256
-static struct dropbear_kex kex_ecdh_nistp256 = {NULL, 0, &ecc_curve_nistp256, &sha256_desc };
+static struct dropbear_kex kex_ecdh_nistp256 = {DROPBEAR_KEX_ECDH, NULL, 0, &ecc_curve_nistp256, &sha256_desc };
 #endif
 #ifdef DROPBEAR_ECC_384
-static struct dropbear_kex kex_ecdh_nistp384 = {NULL, 0, &ecc_curve_nistp384, &sha384_desc };
+static struct dropbear_kex kex_ecdh_nistp384 = {DROPBEAR_KEX_ECDH, NULL, 0, &ecc_curve_nistp384, &sha384_desc };
 #endif
 #ifdef DROPBEAR_ECC_521
-static struct dropbear_kex kex_ecdh_nistp521 = {NULL, 0, &ecc_curve_nistp521, &sha512_desc };
+static struct dropbear_kex kex_ecdh_nistp521 = {DROPBEAR_KEX_ECDH, NULL, 0, &ecc_curve_nistp521, &sha512_desc };
 #endif
-#endif // DROPBEAR_ECDH
+#endif /* DROPBEAR_ECDH */
 
+#ifdef DROPBEAR_CURVE25519
+/* Referred to directly */
+static const struct dropbear_kex kex_curve25519 = {DROPBEAR_KEX_CURVE25519, NULL, 0, NULL, &sha256_desc };
+#endif
 
 algo_type sshkex[] = {
+#ifdef DROPBEAR_CURVE25519
+	{"curve25519-sha256@libssh.org", 0, &kex_curve25519, 1, NULL},
+#endif
 #ifdef DROPBEAR_ECDH
 #ifdef DROPBEAR_ECC_521
 	{"ecdh-sha2-nistp521", 0, &kex_ecdh_nistp521, 1, NULL},
@@ -289,7 +298,7 @@ void buf_put_algolist(buffer * buf, algo_type localalgos[]) {
 	unsigned int donefirst = 0;
 	buffer *algolist = NULL;
 
-	algolist = buf_new(160);
+	algolist = buf_new(200);
 	for (i = 0; localalgos[i].name != NULL; i++) {
 		if (localalgos[i].usable) {
 			if (donefirst)
diff --git a/common-kex.c b/common-kex.c
index a32ca6d..a304d02 100644
--- a/common-kex.c
+++ b/common-kex.c
@@ -577,7 +577,7 @@ struct kex_dh_param *gen_kexdh_param() {
 	TRACE(("enter gen_kexdh_vals"))
 
 	struct kex_dh_param *param = m_malloc(sizeof(*param));
-	m_mp_init_multi(&param->pub, &param->priv, NULL);
+	m_mp_init_multi(&param->pub, &param->priv, &dh_g, &dh_p, &dh_q, NULL);
 
 	/* read the prime and generator*/
 	load_dh_p(&dh_p);
@@ -690,8 +690,8 @@ void kexecdh_comb_key(struct kex_ecdh_param *param, buffer *pub_them,
 
 	ses.dh_K = dropbear_ecc_shared_secret(Q_them, &param->key);
 
-	/* From here on, the code needs to work with the _same_ vars on each side,
-	 * not vice-versaing for client/server */
+	/* Create the remainder of the hash buffer, to generate the exchange hash
+	   See RFC5656 section 4 page 7 */
 	if (IS_DROPBEAR_CLIENT) {
 		Q_C = &param->key;
 		Q_S = Q_them;
@@ -700,7 +700,6 @@ void kexecdh_comb_key(struct kex_ecdh_param *param, buffer *pub_them,
 		Q_S = &param->key;
 	} 
 
-	/* Create the remainder of the hash buffer, to generate the exchange hash */
 	/* K_S, the host key */
 	buf_put_pub_key(ses.kexhashbuf, hostkey, ses.newkeys->algo_hostkey);
 	/* Q_C, client's ephemeral public key octet string */
@@ -713,7 +712,71 @@ void kexecdh_comb_key(struct kex_ecdh_param *param, buffer *pub_them,
 	/* calculate the hash H to sign */
 	finish_kexhashbuf();
 }
-#endif
+#endif /* DROPBEAR_ECDH */
+
+#ifdef DROPBEAR_CURVE25519
+struct kex_curve25519_param *gen_kexcurve25519_param () {
+	/* Per http://cr.yp.to/ecdh.html */
+	struct kex_curve25519_param *param = m_malloc(sizeof(*param));
+	const unsigned char basepoint[32] = {9};
+
+	genrandom(param->priv, CURVE25519_LEN);
+	param->priv[0] &= 248;
+	param->priv[31] &= 127;
+	param->priv[31] |= 64;
+
+	curve25519_donna(param->pub, param->priv, basepoint);
+
+	return param;
+}
+
+void free_kexcurve25519_param(struct kex_curve25519_param *param)
+{
+	m_burn(param->priv, CURVE25519_LEN);
+	m_free(param);
+}
+
+void kexcurve25519_comb_key(struct kex_curve25519_param *param, buffer *buf_pub_them,
+	sign_key *hostkey) {
+	unsigned char out[CURVE25519_LEN];
+	const unsigned char* Q_C = NULL;
+	const unsigned char* Q_S = NULL;
+
+	if (buf_pub_them->len != CURVE25519_LEN)
+	{
+		dropbear_exit("Bad curve25519");
+	}
+
+	curve25519_donna(out, param->priv, buf_pub_them->data);
+	m_mp_alloc_init_multi(&ses.dh_K, NULL);
+	bytes_to_mp(ses.dh_K, out, CURVE25519_LEN);
+	m_burn(out, sizeof(out));
+
+	/* Create the remainder of the hash buffer, to generate the exchange hash.
+	   See RFC5656 section 4 page 7 */
+	if (IS_DROPBEAR_CLIENT) {
+		Q_C = param->pub;
+		Q_S = buf_pub_them->data;
+	} else {
+		Q_S = param->pub;
+		Q_C = buf_pub_them->data;
+	}
+
+	/* K_S, the host key */
+	buf_put_pub_key(ses.kexhashbuf, hostkey, ses.newkeys->algo_hostkey);
+	/* Q_C, client's ephemeral public key octet string */
+	buf_putstring(ses.kexhashbuf, Q_C, CURVE25519_LEN);
+	/* Q_S, server's ephemeral public key octet string */
+	buf_putstring(ses.kexhashbuf, Q_S, CURVE25519_LEN);
+	/* K, the shared secret */
+	buf_putmpint(ses.kexhashbuf, ses.dh_K);
+
+	/* calculate the hash H to sign */
+	finish_kexhashbuf();
+}
+#endif /* DROPBEAR_CURVE25519 */
+
+
 
 static void finish_kexhashbuf(void) {
 	hash_state hs;
diff --git a/curve25519-donna.c b/curve25519-donna.c
new file mode 100644
index 0000000..bb1262e
--- /dev/null
+++ b/curve25519-donna.c
@@ -0,0 +1,734 @@
+/* Copyright 2008, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * curve25519-donna: Curve25519 elliptic curve, public key function
+ *
+ * http://code.google.com/p/curve25519-donna/
+ *
+ * Adam Langley <agl@imperialviolet.org>
+ *
+ * Derived from public domain C code by Daniel J. Bernstein <djb@cr.yp.to>
+ *
+ * More information about curve25519 can be found here
+ *   http://cr.yp.to/ecdh.html
+ *
+ * djb's sample implementation of curve25519 is written in a special assembly
+ * language called qhasm and uses the floating point registers.
+ *
+ * This is, almost, a clean room reimplementation from the curve25519 paper. It
+ * uses many of the tricks described therein. Only the crecip function is taken
+ * from the sample implementation.
+ */
+
+#include <string.h>
+#include <stdint.h>
+
+#ifdef _MSC_VER
+#define inline __inline
+#endif
+
+typedef uint8_t u8;
+typedef int32_t s32;
+typedef int64_t limb;
+
+/* Field element representation:
+ *
+ * Field elements are written as an array of signed, 64-bit limbs, least
+ * significant first. The value of the field element is:
+ *   x[0] + 2^26·x[1] + x^51·x[2] + 2^102·x[3] + ...
+ *
+ * i.e. the limbs are 26, 25, 26, 25, ... bits wide.
+ */
+
+/* Sum two numbers: output += in */
+static void fsum(limb *output, const limb *in) {
+  unsigned i;
+  for (i = 0; i < 10; i += 2) {
+    output[0+i] = (output[0+i] + in[0+i]);
+    output[1+i] = (output[1+i] + in[1+i]);
+  }
+}
+
+/* Find the difference of two numbers: output = in - output
+ * (note the order of the arguments!)
+ */
+static void fdifference(limb *output, const limb *in) {
+  unsigned i;
+  for (i = 0; i < 10; ++i) {
+    output[i] = (in[i] - output[i]);
+  }
+}
+
+/* Multiply a number by a scalar: output = in * scalar */
+static void fscalar_product(limb *output, const limb *in, const limb scalar) {
+  unsigned i;
+  for (i = 0; i < 10; ++i) {
+    output[i] = in[i] * scalar;
+  }
+}
+
+/* Multiply two numbers: output = in2 * in
+ *
+ * output must be distinct to both inputs. The inputs are reduced coefficient
+ * form, the output is not.
+ */
+static void fproduct(limb *output, const limb *in2, const limb *in) {
+  output[0] =       ((limb) ((s32) in2[0])) * ((s32) in[0]);
+  output[1] =       ((limb) ((s32) in2[0])) * ((s32) in[1]) +
+                    ((limb) ((s32) in2[1])) * ((s32) in[0]);
+  output[2] =  2 *  ((limb) ((s32) in2[1])) * ((s32) in[1]) +
+                    ((limb) ((s32) in2[0])) * ((s32) in[2]) +
+                    ((limb) ((s32) in2[2])) * ((s32) in[0]);
+  output[3] =       ((limb) ((s32) in2[1])) * ((s32) in[2]) +
+                    ((limb) ((s32) in2[2])) * ((s32) in[1]) +
+                    ((limb) ((s32) in2[0])) * ((s32) in[3]) +
+                    ((limb) ((s32) in2[3])) * ((s32) in[0]);
+  output[4] =       ((limb) ((s32) in2[2])) * ((s32) in[2]) +
+               2 * (((limb) ((s32) in2[1])) * ((s32) in[3]) +
+                    ((limb) ((s32) in2[3])) * ((s32) in[1])) +
+                    ((limb) ((s32) in2[0])) * ((s32) in[4]) +
+                    ((limb) ((s32) in2[4])) * ((s32) in[0]);
+  output[5] =       ((limb) ((s32) in2[2])) * ((s32) in[3]) +
+                    ((limb) ((s32) in2[3])) * ((s32) in[2]) +
+                    ((limb) ((s32) in2[1])) * ((s32) in[4]) +
+                    ((limb) ((s32) in2[4])) * ((s32) in[1]) +
+                    ((limb) ((s32) in2[0])) * ((s32) in[5]) +
+                    ((limb) ((s32) in2[5])) * ((s32) in[0]);
+  output[6] =  2 * (((limb) ((s32) in2[3])) * ((s32) in[3]) +
+                    ((limb) ((s32) in2[1])) * ((s32) in[5]) +
+                    ((limb) ((s32) in2[5])) * ((s32) in[1])) +
+                    ((limb) ((s32) in2[2])) * ((s32) in[4]) +
+                    ((limb) ((s32) in2[4])) * ((s32) in[2]) +
+                    ((limb) ((s32) in2[0])) * ((s32) in[6]) +
+                    ((limb) ((s32) in2[6])) * ((s32) in[0]);
+  output[7] =       ((limb) ((s32) in2[3])) * ((s32) in[4]) +
+                    ((limb) ((s32) in2[4])) * ((s32) in[3]) +
+                    ((limb) ((s32) in2[2])) * ((s32) in[5]) +
+                    ((limb) ((s32) in2[5])) * ((s32) in[2]) +
+                    ((limb) ((s32) in2[1])) * ((s32) in[6]) +
+                    ((limb) ((s32) in2[6])) * ((s32) in[1]) +
+                    ((limb) ((s32) in2[0])) * ((s32) in[7]) +
+                    ((limb) ((s32) in2[7])) * ((s32) in[0]);
+  output[8] =       ((limb) ((s32) in2[4])) * ((s32) in[4]) +
+               2 * (((limb) ((s32) in2[3])) * ((s32) in[5]) +
+                    ((limb) ((s32) in2[5])) * ((s32) in[3]) +
+                    ((limb) ((s32) in2[1])) * ((s32) in[7]) +
+                    ((limb) ((s32) in2[7])) * ((s32) in[1])) +
+                    ((limb) ((s32) in2[2])) * ((s32) in[6]) +
+                    ((limb) ((s32) in2[6])) * ((s32) in[2]) +
+                    ((limb) ((s32) in2[0])) * ((s32) in[8]) +
+                    ((limb) ((s32) in2[8])) * ((s32) in[0]);
+  output[9] =       ((limb) ((s32) in2[4])) * ((s32) in[5]) +
+                    ((limb) ((s32) in2[5])) * ((s32) in[4]) +
+                    ((limb) ((s32) in2[3])) * ((s32) in[6]) +
+                    ((limb) ((s32) in2[6])) * ((s32) in[3]) +
+                    ((limb) ((s32) in2[2])) * ((s32) in[7]) +
+                    ((limb) ((s32) in2[7])) * ((s32) in[2]) +
+                    ((limb) ((s32) in2[1])) * ((s32) in[8]) +
+                    ((limb) ((s32) in2[8])) * ((s32) in[1]) +
+                    ((limb) ((s32) in2[0])) * ((s32) in[9]) +
+                    ((limb) ((s32) in2[9])) * ((s32) in[0]);
+  output[10] = 2 * (((limb) ((s32) in2[5])) * ((s32) in[5]) +
+                    ((limb) ((s32) in2[3])) * ((s32) in[7]) +
+                    ((limb) ((s32) in2[7])) * ((s32) in[3]) +
+                    ((limb) ((s32) in2[1])) * ((s32) in[9]) +
+                    ((limb) ((s32) in2[9])) * ((s32) in[1])) +
+                    ((limb) ((s32) in2[4])) * ((s32) in[6]) +
+                    ((limb) ((s32) in2[6])) * ((s32) in[4]) +
+                    ((limb) ((s32) in2[2])) * ((s32) in[8]) +
+                    ((limb) ((s32) in2[8])) * ((s32) in[2]);
+  output[11] =      ((limb) ((s32) in2[5])) * ((s32) in[6]) +
+                    ((limb) ((s32) in2[6])) * ((s32) in[5]) +
+                    ((limb) ((s32) in2[4])) * ((s32) in[7]) +
+                    ((limb) ((s32) in2[7])) * ((s32) in[4]) +
+                    ((limb) ((s32) in2[3])) * ((s32) in[8]) +
+                    ((limb) ((s32) in2[8])) * ((s32) in[3]) +
+                    ((limb) ((s32) in2[2])) * ((s32) in[9]) +
+                    ((limb) ((s32) in2[9])) * ((s32) in[2]);
+  output[12] =      ((limb) ((s32) in2[6])) * ((s32) in[6]) +
+               2 * (((limb) ((s32) in2[5])) * ((s32) in[7]) +
+                    ((limb) ((s32) in2[7])) * ((s32) in[5]) +
+                    ((limb) ((s32) in2[3])) * ((s32) in[9]) +
+                    ((limb) ((s32) in2[9])) * ((s32) in[3])) +
+                    ((limb) ((s32) in2[4])) * ((s32) in[8]) +
+                    ((limb) ((s32) in2[8])) * ((s32) in[4]);
+  output[13] =      ((limb) ((s32) in2[6])) * ((s32) in[7]) +
+                    ((limb) ((s32) in2[7])) * ((s32) in[6]) +
+                    ((limb) ((s32) in2[5])) * ((s32) in[8]) +
+                    ((limb) ((s32) in2[8])) * ((s32) in[5]) +
+                    ((limb) ((s32) in2[4])) * ((s32) in[9]) +
+                    ((limb) ((s32) in2[9])) * ((s32) in[4]);
+  output[14] = 2 * (((limb) ((s32) in2[7])) * ((s32) in[7]) +
+                    ((limb) ((s32) in2[5])) * ((s32) in[9]) +
+                    ((limb) ((s32) in2[9])) * ((s32) in[5])) +
+                    ((limb) ((s32) in2[6])) * ((s32) in[8]) +
+                    ((limb) ((s32) in2[8])) * ((s32) in[6]);
+  output[15] =      ((limb) ((s32) in2[7])) * ((s32) in[8]) +
+                    ((limb) ((s32) in2[8])) * ((s32) in[7]) +
+                    ((limb) ((s32) in2[6])) * ((s32) in[9]) +
+                    ((limb) ((s32) in2[9])) * ((s32) in[6]);
+  output[16] =      ((limb) ((s32) in2[8])) * ((s32) in[8]) +
+               2 * (((limb) ((s32) in2[7])) * ((s32) in[9]) +
+                    ((limb) ((s32) in2[9])) * ((s32) in[7]));
+  output[17] =      ((limb) ((s32) in2[8])) * ((s32) in[9]) +
+                    ((limb) ((s32) in2[9])) * ((s32) in[8]);
+  output[18] = 2 *  ((limb) ((s32) in2[9])) * ((s32) in[9]);
+}
+
+/* Reduce a long form to a short form by taking the input mod 2^255 - 19. */
+static void freduce_degree(limb *output) {
+  /* Each of these shifts and adds ends up multiplying the value by 19. */
+  output[8] += output[18] << 4;
+  output[8] += output[18] << 1;
+  output[8] += output[18];
+  output[7] += output[17] << 4;
+  output[7] += output[17] << 1;
+  output[7] += output[17];
+  output[6] += output[16] << 4;
+  output[6] += output[16] << 1;
+  output[6] += output[16];
+  output[5] += output[15] << 4;
+  output[5] += output[15] << 1;
+  output[5] += output[15];
+  output[4] += output[14] << 4;
+  output[4] += output[14] << 1;
+  output[4] += output[14];
+  output[3] += output[13] << 4;
+  output[3] += output[13] << 1;
+  output[3] += output[13];
+  output[2] += output[12] << 4;
+  output[2] += output[12] << 1;
+  output[2] += output[12];
+  output[1] += output[11] << 4;
+  output[1] += output[11] << 1;
+  output[1] += output[11];
+  output[0] += output[10] << 4;
+  output[0] += output[10] << 1;
+  output[0] += output[10];
+}
+
+#if (-1 & 3) != 3
+#error "This code only works on a two's complement system"
+#endif
+
+/* return v / 2^26, using only shifts and adds. */
+static inline limb
+div_by_2_26(const limb v)
+{
+  /* High word of v; no shift needed*/
+  const uint32_t highword = (uint32_t) (((uint64_t) v) >> 32);
+  /* Set to all 1s if v was negative; else set to 0s. */
+  const int32_t sign = ((int32_t) highword) >> 31;
+  /* Set to 0x3ffffff if v was negative; else set to 0. */
+  const int32_t roundoff = ((uint32_t) sign) >> 6;
+  /* Should return v / (1<<26) */
+  return (v + roundoff) >> 26;
+}
+
+/* return v / (2^25), using only shifts and adds. */
+static inline limb
+div_by_2_25(const limb v)
+{
+  /* High word of v; no shift needed*/
+  const uint32_t highword = (uint32_t) (((uint64_t) v) >> 32);
+  /* Set to all 1s if v was negative; else set to 0s. */
+  const int32_t sign = ((int32_t) highword) >> 31;
+  /* Set to 0x1ffffff if v was negative; else set to 0. */
+  const int32_t roundoff = ((uint32_t) sign) >> 7;
+  /* Should return v / (1<<25) */
+  return (v + roundoff) >> 25;
+}
+
+static inline s32
+div_s32_by_2_25(const s32 v)
+{
+   const s32 roundoff = ((uint32_t)(v >> 31)) >> 7;
+   return (v + roundoff) >> 25;
+}
+
+/* Reduce all coefficients of the short form input so that |x| < 2^26.
+ *
+ * On entry: |output[i]| < 2^62
+ */
+static void freduce_coefficients(limb *output) {
+  unsigned i;
+
+  output[10] = 0;
+
+  for (i = 0; i < 10; i += 2) {
+    limb over = div_by_2_26(output[i]);
+    output[i] -= over << 26;
+    output[i+1] += over;
+
+    over = div_by_2_25(output[i+1]);
+    output[i+1] -= over << 25;
+    output[i+2] += over;
+  }
+  /* Now |output[10]| < 2 ^ 38 and all other coefficients are reduced. */
+  output[0] += output[10] << 4;
+  output[0] += output[10] << 1;
+  output[0] += output[10];
+
+  output[10] = 0;
+
+  /* Now output[1..9] are reduced, and |output[0]| < 2^26 + 19 * 2^38
+   * So |over| will be no more than 77825  */
+  {
+    limb over = div_by_2_26(output[0]);
+    output[0] -= over << 26;
+    output[1] += over;
+  }
+
+  /* Now output[0,2..9] are reduced, and |output[1]| < 2^25 + 77825
+   * So |over| will be no more than 1. */
+  {
+    /* output[1] fits in 32 bits, so we can use div_s32_by_2_25 here. */
+    s32 over32 = div_s32_by_2_25((s32) output[1]);
+    output[1] -= over32 << 25;
+    output[2] += over32;
+  }
+
+  /* Finally, output[0,1,3..9] are reduced, and output[2] is "nearly reduced":
+   * we have |output[2]| <= 2^26.  This is good enough for all of our math,
+   * but it will require an extra freduce_coefficients before fcontract. */
+}
+
+/* A helpful wrapper around fproduct: output = in * in2.
+ *
+ * output must be distinct to both inputs. The output is reduced degree and
+ * reduced coefficient.
+ */
+static void
+fmul(limb *output, const limb *in, const limb *in2) {
+  limb t[19];
+  fproduct(t, in, in2);
+  freduce_degree(t);
+  freduce_coefficients(t);
+  memcpy(output, t, sizeof(limb) * 10);
+}
+
+static void fsquare_inner(limb *output, const limb *in) {
+  output[0] =       ((limb) ((s32) in[0])) * ((s32) in[0]);
+  output[1] =  2 *  ((limb) ((s32) in[0])) * ((s32) in[1]);
+  output[2] =  2 * (((limb) ((s32) in[1])) * ((s32) in[1]) +
+                    ((limb) ((s32) in[0])) * ((s32) in[2]));
+  output[3] =  2 * (((limb) ((s32) in[1])) * ((s32) in[2]) +
+                    ((limb) ((s32) in[0])) * ((s32) in[3]));
+  output[4] =       ((limb) ((s32) in[2])) * ((s32) in[2]) +
+               4 *  ((limb) ((s32) in[1])) * ((s32) in[3]) +
+               2 *  ((limb) ((s32) in[0])) * ((s32) in[4]);
+  output[5] =  2 * (((limb) ((s32) in[2])) * ((s32) in[3]) +
+                    ((limb) ((s32) in[1])) * ((s32) in[4]) +
+                    ((limb) ((s32) in[0])) * ((s32) in[5]));
+  output[6] =  2 * (((limb) ((s32) in[3])) * ((s32) in[3]) +
+                    ((limb) ((s32) in[2])) * ((s32) in[4]) +
+                    ((limb) ((s32) in[0])) * ((s32) in[6]) +
+               2 *  ((limb) ((s32) in[1])) * ((s32) in[5]));
+  output[7] =  2 * (((limb) ((s32) in[3])) * ((s32) in[4]) +
+                    ((limb) ((s32) in[2])) * ((s32) in[5]) +
+                    ((limb) ((s32) in[1])) * ((s32) in[6]) +
+                    ((limb) ((s32) in[0])) * ((s32) in[7]));
+  output[8] =       ((limb) ((s32) in[4])) * ((s32) in[4]) +
+               2 * (((limb) ((s32) in[2])) * ((s32) in[6]) +
+                    ((limb) ((s32) in[0])) * ((s32) in[8]) +
+               2 * (((limb) ((s32) in[1])) * ((s32) in[7]) +
+                    ((limb) ((s32) in[3])) * ((s32) in[5])));
+  output[9] =  2 * (((limb) ((s32) in[4])) * ((s32) in[5]) +
+                    ((limb) ((s32) in[3])) * ((s32) in[6]) +
+                    ((limb) ((s32) in[2])) * ((s32) in[7]) +
+                    ((limb) ((s32) in[1])) * ((s32) in[8]) +
+                    ((limb) ((s32) in[0])) * ((s32) in[9]));
+  output[10] = 2 * (((limb) ((s32) in[5])) * ((s32) in[5]) +
+                    ((limb) ((s32) in[4])) * ((s32) in[6]) +
+                    ((limb) ((s32) in[2])) * ((s32) in[8]) +
+               2 * (((limb) ((s32) in[3])) * ((s32) in[7]) +
+                    ((limb) ((s32) in[1])) * ((s32) in[9])));
+  output[11] = 2 * (((limb) ((s32) in[5])) * ((s32) in[6]) +
+                    ((limb) ((s32) in[4])) * ((s32) in[7]) +
+                    ((limb) ((s32) in[3])) * ((s32) in[8]) +
+                    ((limb) ((s32) in[2])) * ((s32) in[9]));
+  output[12] =      ((limb) ((s32) in[6])) * ((s32) in[6]) +
+               2 * (((limb) ((s32) in[4])) * ((s32) in[8]) +
+               2 * (((limb) ((s32) in[5])) * ((s32) in[7]) +
+                    ((limb) ((s32) in[3])) * ((s32) in[9])));
+  output[13] = 2 * (((limb) ((s32) in[6])) * ((s32) in[7]) +
+                    ((limb) ((s32) in[5])) * ((s32) in[8]) +
+                    ((limb) ((s32) in[4])) * ((s32) in[9]));
+  output[14] = 2 * (((limb) ((s32) in[7])) * ((s32) in[7]) +
+                    ((limb) ((s32) in[6])) * ((s32) in[8]) +
+               2 *  ((limb) ((s32) in[5])) * ((s32) in[9]));
+  output[15] = 2 * (((limb) ((s32) in[7])) * ((s32) in[8]) +
+                    ((limb) ((s32) in[6])) * ((s32) in[9]));
+  output[16] =      ((limb) ((s32) in[8])) * ((s32) in[8]) +
+               4 *  ((limb) ((s32) in[7])) * ((s32) in[9]);
+  output[17] = 2 *  ((limb) ((s32) in[8])) * ((s32) in[9]);
+  output[18] = 2 *  ((limb) ((s32) in[9])) * ((s32) in[9]);
+}
+
+static void
+fsquare(limb *output, const limb *in) {
+  limb t[19];
+  fsquare_inner(t, in);
+  freduce_degree(t);
+  freduce_coefficients(t);
+  memcpy(output, t, sizeof(limb) * 10);
+}
+
+/* Take a little-endian, 32-byte number and expand it into polynomial form */
+static void
+fexpand(limb *output, const u8 *input) {
+#define F(n,start,shift,mask) \
+  output[n] = ((((limb) input[start + 0]) | \
+                ((limb) input[start + 1]) << 8 | \
+                ((limb) input[start + 2]) << 16 | \
+                ((limb) input[start + 3]) << 24) >> shift) & mask;
+  F(0, 0, 0, 0x3ffffff);
+  F(1, 3, 2, 0x1ffffff);
+  F(2, 6, 3, 0x3ffffff);
+  F(3, 9, 5, 0x1ffffff);
+  F(4, 12, 6, 0x3ffffff);
+  F(5, 16, 0, 0x1ffffff);
+  F(6, 19, 1, 0x3ffffff);
+  F(7, 22, 3, 0x1ffffff);
+  F(8, 25, 4, 0x3ffffff);
+  F(9, 28, 6, 0x3ffffff);
+#undef F
+}
+
+#if (-32 >> 1) != -16
+#error "This code only works when >> does sign-extension on negative numbers"
+#endif
+
+/* Take a fully reduced polynomial form number and contract it into a
+ * little-endian, 32-byte array
+ */
+static void
+fcontract(u8 *output, limb *input) {
+  int i;
+  int j;
+
+  for (j = 0; j < 2; ++j) {
+    for (i = 0; i < 9; ++i) {
+      if ((i & 1) == 1) {
+        /* This calculation is a time-invariant way to make input[i] positive
+           by borrowing from the next-larger limb.
+        */
+        const s32 mask = (s32)(input[i]) >> 31;
+        const s32 carry = -(((s32)(input[i]) & mask) >> 25);
+        input[i] = (s32)(input[i]) + (carry << 25);
+        input[i+1] = (s32)(input[i+1]) - carry;
+      } else {
+        const s32 mask = (s32)(input[i]) >> 31;
+        const s32 carry = -(((s32)(input[i]) & mask) >> 26);
+        input[i] = (s32)(input[i]) + (carry << 26);
+        input[i+1] = (s32)(input[i+1]) - carry;
+      }
+    }
+    {
+      const s32 mask = (s32)(input[9]) >> 31;
+      const s32 carry = -(((s32)(input[9]) & mask) >> 25);
+      input[9] = (s32)(input[9]) + (carry << 25);
+      input[0] = (s32)(input[0]) - (carry * 19);
+    }
+  }
+
+  /* The first borrow-propagation pass above ended with every limb
+     except (possibly) input[0] non-negative.
+
+     Since each input limb except input[0] is decreased by at most 1
+     by a borrow-propagation pass, the second borrow-propagation pass
+     could only have wrapped around to decrease input[0] again if the
+     first pass left input[0] negative *and* input[1] through input[9]
+     were all zero.  In that case, input[1] is now 2^25 - 1, and this
+     last borrow-propagation step will leave input[1] non-negative.
+  */
+  {
+    const s32 mask = (s32)(input[0]) >> 31;
+    const s32 carry = -(((s32)(input[0]) & mask) >> 26);
+    input[0] = (s32)(input[0]) + (carry << 26);
+    input[1] = (s32)(input[1]) - carry;
+  }
+
+  /* Both passes through the above loop, plus the last 0-to-1 step, are
+     necessary: if input[9] is -1 and input[0] through input[8] are 0,
+     negative values will remain in the array until the end.
+   */
+
+  input[1] <<= 2;
+  input[2] <<= 3;
+  input[3] <<= 5;
+  input[4] <<= 6;
+  input[6] <<= 1;
+  input[7] <<= 3;
+  input[8] <<= 4;
+  input[9] <<= 6;
+#define F(i, s) \
+  output[s+0] |=  input[i] & 0xff; \
+  output[s+1]  = (input[i] >> 8) & 0xff; \
+  output[s+2]  = (input[i] >> 16) & 0xff; \
+  output[s+3]  = (input[i] >> 24) & 0xff;
+  output[0] = 0;
+  output[16] = 0;
+  F(0,0);
+  F(1,3);
+  F(2,6);
+  F(3,9);
+  F(4,12);
+  F(5,16);
+  F(6,19);
+  F(7,22);
+  F(8,25);
+  F(9,28);
+#undef F
+}
+
+/* Input: Q, Q', Q-Q'
+ * Output: 2Q, Q+Q'
+ *
+ *   x2 z3: long form
+ *   x3 z3: long form
+ *   x z: short form, destroyed
+ *   xprime zprime: short form, destroyed
+ *   qmqp: short form, preserved
+ */
+static void fmonty(limb *x2, limb *z2,  /* output 2Q */
+                   limb *x3, limb *z3,  /* output Q + Q' */
+                   limb *x, limb *z,    /* input Q */
+                   limb *xprime, limb *zprime,  /* input Q' */
+                   const limb *qmqp /* input Q - Q' */) {
+  limb origx[10], origxprime[10], zzz[19], xx[19], zz[19], xxprime[19],
+        zzprime[19], zzzprime[19], xxxprime[19];
+
+  memcpy(origx, x, 10 * sizeof(limb));
+  fsum(x, z);
+  fdifference(z, origx);  // does x - z
+
+  memcpy(origxprime, xprime, sizeof(limb) * 10);
+  fsum(xprime, zprime);
+  fdifference(zprime, origxprime);
+  fproduct(xxprime, xprime, z);
+  fproduct(zzprime, x, zprime);
+  freduce_degree(xxprime);
+  freduce_coefficients(xxprime);
+  freduce_degree(zzprime);
+  freduce_coefficients(zzprime);
+  memcpy(origxprime, xxprime, sizeof(limb) * 10);
+  fsum(xxprime, zzprime);
+  fdifference(zzprime, origxprime);
+  fsquare(xxxprime, xxprime);
+  fsquare(zzzprime, zzprime);
+  fproduct(zzprime, zzzprime, qmqp);
+  freduce_degree(zzprime);
+  freduce_coefficients(zzprime);
+  memcpy(x3, xxxprime, sizeof(limb) * 10);
+  memcpy(z3, zzprime, sizeof(limb) * 10);
+
+  fsquare(xx, x);
+  fsquare(zz, z);
+  fproduct(x2, xx, zz);
+  freduce_degree(x2);
+  freduce_coefficients(x2);
+  fdifference(zz, xx);  // does zz = xx - zz
+  memset(zzz + 10, 0, sizeof(limb) * 9);
+  fscalar_product(zzz, zz, 121665);
+  /* No need to call freduce_degree here:
+     fscalar_product doesn't increase the degree of its input. */
+  freduce_coefficients(zzz);
+  fsum(zzz, xx);
+  fproduct(z2, zz, zzz);
+  freduce_degree(z2);
+  freduce_coefficients(z2);
+}
+
+/* Conditionally swap two reduced-form limb arrays if 'iswap' is 1, but leave
+ * them unchanged if 'iswap' is 0.  Runs in data-invariant time to avoid
+ * side-channel attacks.
+ *
+ * NOTE that this function requires that 'iswap' be 1 or 0; other values give
+ * wrong results.  Also, the two limb arrays must be in reduced-coefficient,
+ * reduced-degree form: the values in a[10..19] or b[10..19] aren't swapped,
+ * and all all values in a[0..9],b[0..9] must have magnitude less than
+ * INT32_MAX.
+ */
+static void
+swap_conditional(limb a[19], limb b[19], limb iswap) {
+  unsigned i;
+  const s32 swap = (s32) -iswap;
+
+  for (i = 0; i < 10; ++i) {
+    const s32 x = swap & ( ((s32)a[i]) ^ ((s32)b[i]) );
+    a[i] = ((s32)a[i]) ^ x;
+    b[i] = ((s32)b[i]) ^ x;
+  }
+}
+
+/* Calculates nQ where Q is the x-coordinate of a point on the curve
+ *
+ *   resultx/resultz: the x coordinate of the resulting curve point (short form)
+ *   n: a little endian, 32-byte number
+ *   q: a point of the curve (short form)
+ */
+static void
+cmult(limb *resultx, limb *resultz, const u8 *n, const limb *q) {
+  limb a[19] = {0}, b[19] = {1}, c[19] = {1}, d[19] = {0};
+  limb *nqpqx = a, *nqpqz = b, *nqx = c, *nqz = d, *t;
+  limb e[19] = {0}, f[19] = {1}, g[19] = {0}, h[19] = {1};
+  limb *nqpqx2 = e, *nqpqz2 = f, *nqx2 = g, *nqz2 = h;
+
+  unsigned i, j;
+
+  memcpy(nqpqx, q, sizeof(limb) * 10);
+
+  for (i = 0; i < 32; ++i) {
+    u8 byte = n[31 - i];
+    for (j = 0; j < 8; ++j) {
+      const limb bit = byte >> 7;
+
+      swap_conditional(nqx, nqpqx, bit);
+      swap_conditional(nqz, nqpqz, bit);
+      fmonty(nqx2, nqz2,
+             nqpqx2, nqpqz2,
+             nqx, nqz,
+             nqpqx, nqpqz,
+             q);
+      swap_conditional(nqx2, nqpqx2, bit);
+      swap_conditional(nqz2, nqpqz2, bit);
+
+      t = nqx;
+      nqx = nqx2;
+      nqx2 = t;
+      t = nqz;
+      nqz = nqz2;
+      nqz2 = t;
+      t = nqpqx;
+      nqpqx = nqpqx2;
+      nqpqx2 = t;
+      t = nqpqz;
+      nqpqz = nqpqz2;
+      nqpqz2 = t;
+
+      byte <<= 1;
+    }
+  }
+
+  memcpy(resultx, nqx, sizeof(limb) * 10);
+  memcpy(resultz, nqz, sizeof(limb) * 10);
+}
+
+// -----------------------------------------------------------------------------
+// Shamelessly copied from djb's code
+// -----------------------------------------------------------------------------
+static void
+crecip(limb *out, const limb *z) {
+  limb z2[10];
+  limb z9[10];
+  limb z11[10];
+  limb z2_5_0[10];
+  limb z2_10_0[10];
+  limb z2_20_0[10];
+  limb z2_50_0[10];
+  limb z2_100_0[10];
+  limb t0[10];
+  limb t1[10];
+  int i;
+
+  /* 2 */ fsquare(z2,z);
+  /* 4 */ fsquare(t1,z2);
+  /* 8 */ fsquare(t0,t1);
+  /* 9 */ fmul(z9,t0,z);
+  /* 11 */ fmul(z11,z9,z2);
+  /* 22 */ fsquare(t0,z11);
+  /* 2^5 - 2^0 = 31 */ fmul(z2_5_0,t0,z9);
+
+  /* 2^6 - 2^1 */ fsquare(t0,z2_5_0);
+  /* 2^7 - 2^2 */ fsquare(t1,t0);
+  /* 2^8 - 2^3 */ fsquare(t0,t1);
+  /* 2^9 - 2^4 */ fsquare(t1,t0);
+  /* 2^10 - 2^5 */ fsquare(t0,t1);
+  /* 2^10 - 2^0 */ fmul(z2_10_0,t0,z2_5_0);
+
+  /* 2^11 - 2^1 */ fsquare(t0,z2_10_0);
+  /* 2^12 - 2^2 */ fsquare(t1,t0);
+  /* 2^20 - 2^10 */ for (i = 2;i < 10;i += 2) { fsquare(t0,t1); fsquare(t1,t0); }
+  /* 2^20 - 2^0 */ fmul(z2_20_0,t1,z2_10_0);
+
+  /* 2^21 - 2^1 */ fsquare(t0,z2_20_0);
+  /* 2^22 - 2^2 */ fsquare(t1,t0);
+  /* 2^40 - 2^20 */ for (i = 2;i < 20;i += 2) { fsquare(t0,t1); fsquare(t1,t0); }
+  /* 2^40 - 2^0 */ fmul(t0,t1,z2_20_0);
+
+  /* 2^41 - 2^1 */ fsquare(t1,t0);
+  /* 2^42 - 2^2 */ fsquare(t0,t1);
+  /* 2^50 - 2^10 */ for (i = 2;i < 10;i += 2) { fsquare(t1,t0); fsquare(t0,t1); }
+  /* 2^50 - 2^0 */ fmul(z2_50_0,t0,z2_10_0);
+
+  /* 2^51 - 2^1 */ fsquare(t0,z2_50_0);
+  /* 2^52 - 2^2 */ fsquare(t1,t0);
+  /* 2^100 - 2^50 */ for (i = 2;i < 50;i += 2) { fsquare(t0,t1); fsquare(t1,t0); }
+  /* 2^100 - 2^0 */ fmul(z2_100_0,t1,z2_50_0);
+
+  /* 2^101 - 2^1 */ fsquare(t1,z2_100_0);
+  /* 2^102 - 2^2 */ fsquare(t0,t1);
+  /* 2^200 - 2^100 */ for (i = 2;i < 100;i += 2) { fsquare(t1,t0); fsquare(t0,t1); }
+  /* 2^200 - 2^0 */ fmul(t1,t0,z2_100_0);
+
+  /* 2^201 - 2^1 */ fsquare(t0,t1);
+  /* 2^202 - 2^2 */ fsquare(t1,t0);
+  /* 2^250 - 2^50 */ for (i = 2;i < 50;i += 2) { fsquare(t0,t1); fsquare(t1,t0); }
+  /* 2^250 - 2^0 */ fmul(t0,t1,z2_50_0);
+
+  /* 2^251 - 2^1 */ fsquare(t1,t0);
+  /* 2^252 - 2^2 */ fsquare(t0,t1);
+  /* 2^253 - 2^3 */ fsquare(t1,t0);
+  /* 2^254 - 2^4 */ fsquare(t0,t1);
+  /* 2^255 - 2^5 */ fsquare(t1,t0);
+  /* 2^255 - 21 */ fmul(out,t1,z11);
+}
+
+int curve25519_donna(u8 *, const u8 *, const u8 *);
+
+int
+curve25519_donna(u8 *mypublic, const u8 *secret, const u8 *basepoint) {
+  limb bp[10], x[10], z[11], zmone[10];
+  uint8_t e[32];
+  int i;
+
+  for (i = 0; i < 32; ++i) e[i] = secret[i];
+  e[0] &= 248;
+  e[31] &= 127;
+  e[31] |= 64;
+
+  fexpand(bp, basepoint);
+  cmult(x, z, e, bp);
+  crecip(zmone, z);
+  fmul(z, x, zmone);
+  freduce_coefficients(z);
+  fcontract(mypublic, z);
+  return 0;
+}
diff --git a/debug.h b/debug.h
index a761c2e..289c577 100644
--- a/debug.h
+++ b/debug.h
@@ -40,7 +40,6 @@
  * since the printing may not sanitise strings etc. This will add a reasonable
  * amount to your executable size. */
 /* #define DEBUG_TRACE */
-#define DEBUG_TRACE
 
 /* All functions writing to the cleartext payload buffer call
  * CHECKCLEARTOWRITE() before writing. This is only really useful if you're
@@ -72,7 +71,7 @@
 
 /* To debug with GDB it is easier to run with no forking of child processes.
    You will need to pass "-F" as well. */
-#define DEBUG_NOFORK
+/* #define DEBUG_NOFORK */
 
 
 /* For testing as non-root on shadowed systems, include the crypt of a password
diff --git a/dropbearkey.c b/dropbearkey.c
index 57db3af..01385a1 100644
--- a/dropbearkey.c
+++ b/dropbearkey.c
@@ -54,15 +54,13 @@
 #include "ecdsa.h"
 #include "crypto_desc.h"
 #include "random.h"
+#include "gensignkey.h"
 
 static void printhelp(char * progname);
 
-#define RSA_DEFAULT_SIZE 2048
-#define DSS_DEFAULT_SIZE 1024
 
-static void buf_writefile(buffer * buf, const char * filename);
 static void printpubkey(sign_key * key, int keytype);
-static void justprintpub(const char* filename);
+static int printpubfile(const char* filename);
 
 /* Print a help message */
 static void printhelp(char * progname) {
@@ -103,6 +101,30 @@ static void printhelp(char * progname) {
 					,progname);
 }
 
+/* fails fatally */
+static void check_signkey_bits(enum signkey_type type, int bits)
+{
+        switch (type) {
+#ifdef DROPBEAR_RSA
+            case DROPBEAR_SIGNKEY_RSA:
+                if (bits < 512 || bits > 4096 || (bits % 8 != 0)) {
+                	dropbear_exit("Bits must satisfy 512 <= bits <= 4096, and be a"
+                            " multiple of 8\n");
+                }
+                break;
+#endif
+#ifdef DROPEAR_DSS
+            case DROPBEAR_SIGNKEY_DSS:
+                if (bits != 1024) {
+                    dropbear_exit("DSS keys have a fixed size of 1024 bits\n");
+                    exit(EXIT_FAILURE);
+                }
+#endif
+			default:
+				(void)0; /* quiet, compiler. ecdsa handles checks itself */
+        }
+}
+
 #if defined(DBMULTI_dropbearkey) || !defined(DROPBEAR_MULTI)
 #if defined(DBMULTI_dropbearkey) && defined(DROPBEAR_MULTI)
 int dropbearkey_main(int argc, char ** argv) {
@@ -112,13 +134,11 @@ int main(int argc, char ** argv) {
 
 	int i;
 	char ** next = 0;
-	sign_key *key = NULL;
-	buffer *buf = NULL;
 	char * filename = NULL;
 	enum signkey_type keytype = DROPBEAR_SIGNKEY_NONE;
 	char * typetext = NULL;
 	char * sizetext = NULL;
-	unsigned int bits;
+	unsigned int bits = 0;
 	int printpub = 0;
 
 	crypto_init();
@@ -174,8 +194,8 @@ int main(int argc, char ** argv) {
 	}
 
 	if (printpub) {
-		justprintpub(filename);
-		/* Not reached */
+		int ret = printpubfile(filename);
+		exit(ret);
 	}
 
 	/* check/parse args */
@@ -216,106 +236,22 @@ int main(int argc, char ** argv) {
 			exit(EXIT_FAILURE);
 		}
 		
-		// TODO: put RSA and DSS size checks into genrsa.c etc
-        switch (keytype) {
-#ifdef DROPBEAR_RSA
-            case DROPBEAR_SIGNKEY_RSA:
-                if (bits < 512 || bits > 4096 || (bits % 8 != 0)) {
-                    fprintf(stderr, "Bits must satisfy 512 <= bits <= 4096, and be a"
-                            " multiple of 8\n");
-                    exit(EXIT_FAILURE);
-                }
-                break;
-#endif
-#ifdef DROPEAR_DSS
-            case DROPBEAR_SIGNKEY_DSS:
-                if (bits != 1024) {
-                    fprintf(stderr, "DSS keys have a fixed size of 1024 bits\n");
-                    exit(EXIT_FAILURE);			
-                }
-#endif
-			default:
-				(void)0; /* quiet, compiler. ecdsa handles checks itself */
-        }
-
-    } else {
-    	/* default key size */
-
-        switch (keytype) {
-#ifdef DROPBEAR_RSA
-            case DROPBEAR_SIGNKEY_RSA:
-				bits = RSA_DEFAULT_SIZE;
-                break;
-#endif
-#ifdef DROPBEAR_DSS
-            case DROPBEAR_SIGNKEY_DSS:
-                bits = DSS_DEFAULT_SIZE;
-                break;
-#endif
-#ifdef DROPBEAR_ECDSA
-            case DROPBEAR_SIGNKEY_ECDSA_KEYGEN:
-                bits = ECDSA_DEFAULT_SIZE;
-                break;
-#endif
-            default:
-                exit(EXIT_FAILURE); /* not reached */
-		}
-	}
-
-
-	fprintf(stderr, "Will output %d bit %s secret key to '%s'\n", bits,
-			typetext, filename);
-
-	/* don't want the file readable by others */
-	umask(077);
+		check_signkey_bits(keytype, bits);;
+    }
 
-	/* now we can generate the key */
-	key = new_sign_key();
-	
 	fprintf(stderr, "Generating key, this may take a while...\n");
-	switch(keytype) {
-#ifdef DROPBEAR_RSA
-		case DROPBEAR_SIGNKEY_RSA:
-			key->rsakey = gen_rsa_priv_key(bits);
-			break;
-#endif
-#ifdef DROPBEAR_DSS
-		case DROPBEAR_SIGNKEY_DSS:
-			key->dsskey = gen_dss_priv_key(bits);
-			break;
-#endif
-#ifdef DROPBEAR_ECDSA
-		case DROPBEAR_SIGNKEY_ECDSA_KEYGEN:
-			{
-				ecc_key *ecckey = gen_ecdsa_priv_key(bits);
-				keytype = ecdsa_signkey_type(ecckey);
-				*signkey_key_ptr(key, keytype) = ecckey;
-			}
-			break;
-#endif
-		default:
-			fprintf(stderr, "Internal error, bad key type\n");
-			exit(EXIT_FAILURE);
-	}
+    if (signkey_generate(keytype, bits, filename) == DROPBEAR_FAILURE)
+    {
+    	dropbear_exit("Failed to generate key.\n");
+    }
 
-	buf = buf_new(MAX_PRIVKEY_SIZE); 
-
-	buf_put_priv_key(buf, key, keytype);
-	buf_setpos(buf, 0);
-	buf_writefile(buf, filename);
-
-	buf_burn(buf);
-	buf_free(buf);
-
-	printpubkey(key, keytype);
-
-	sign_key_free(key);
+	printpubfile(filename);
 
 	return EXIT_SUCCESS;
 }
 #endif
 
-static void justprintpub(const char* filename) {
+static int printpubfile(const char* filename) {
 
 	buffer *buf = NULL;
 	sign_key *key = NULL;
@@ -353,7 +289,7 @@ out:
 		sign_key_free(key);
 		key = NULL;
 	}
-	exit(err);
+	return err;
 }
 
 static void printpubkey(sign_key * key, int keytype) {
@@ -402,35 +338,3 @@ static void printpubkey(sign_key * key, int keytype) {
 	m_free(fp);
 	buf_free(buf);
 }
-
-/* Write a buffer to a file specified, failing if the file exists */
-static void buf_writefile(buffer * buf, const char * filename) {
-
-	int fd;
-	int len;
-
-	fd = open(filename, O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
-	if (fd < 0) {
-		fprintf(stderr, "Couldn't create new file %s\n", filename);
-		perror("Reason");
-		buf_burn(buf);
-		exit(EXIT_FAILURE);
-	}
-
-	/* write the file now */
-	while (buf->pos != buf->len) {
-		len = write(fd, buf_getptr(buf, buf->len - buf->pos),
-				buf->len - buf->pos);
-		if (errno == EINTR) {
-			continue;
-		}
-		if (len <= 0) {
-			fprintf(stderr, "Failed writing file '%s'\n",filename);
-			perror("Reason");
-			exit(EXIT_FAILURE);
-		}
-		buf_incrpos(buf, len);
-	}
-
-	close(fd);
-}
diff --git a/ecc.c b/ecc.c
index 3e0763c..5812b18 100644
--- a/ecc.c
+++ b/ecc.c
@@ -6,7 +6,7 @@
 
 #ifdef DROPBEAR_ECC
 
-// .dp members are filled out by dropbear_ecc_fill_dp() at startup
+/* .dp members are filled out by dropbear_ecc_fill_dp() at startup */
 #ifdef DROPBEAR_ECC_256
 struct dropbear_ecc_curve ecc_curve_nistp256 = {
 	.ltc_size = 32,
@@ -44,7 +44,7 @@ struct dropbear_ecc_curve *dropbear_ecc_curves[] = {
 
 void dropbear_ecc_fill_dp() {
 	struct dropbear_ecc_curve **curve;
-	// libtomcrypt guarantees they're ordered by size
+	/* libtomcrypt guarantees they're ordered by size */
 	const ltc_ecc_set_type *dp = ltc_ecc_sets;
 	for (curve = dropbear_ecc_curves; *curve; curve++) {
 		for (;dp->size > 0; dp++) {
diff --git a/ecdsa.c b/ecdsa.c
index 66612e4..eddbf13 100644
--- a/ecdsa.c
+++ b/ecdsa.c
@@ -8,6 +8,13 @@
 
 #ifdef DROPBEAR_ECDSA
 
+int signkey_is_ecdsa(enum signkey_type type)
+{
+	return type == DROPBEAR_SIGNKEY_ECDSA_NISTP256
+		|| type == DROPBEAR_SIGNKEY_ECDSA_NISTP384
+		|| type == DROPBEAR_SIGNKEY_ECDSA_NISTP521;
+}
+
 enum signkey_type ecdsa_signkey_type(ecc_key * key) {
 #ifdef DROPBEAR_ECC_256
 	if (key->dp == ecc_curve_nistp256.dp) {
@@ -239,8 +246,8 @@ out:
 
 // returns values in s and r
 // returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE
-static int buf_get_ecdsa_verify_params(buffer *buf, struct dropbear_ecc_curve *curve,
-	void *r, void* s) {
+static int buf_get_ecdsa_verify_params(buffer *buf,
+			void *r, void* s) {
 	int ret = DROPBEAR_FAILURE;
 	unsigned int sig_len;
 	unsigned int sig_pos;
@@ -295,7 +302,7 @@ int buf_ecdsa_verify(buffer *buf, ecc_key *key, buffer *data_buf) {
 		dropbear_exit("ECC error");
 	}
 
-	if (buf_get_ecdsa_verify_params(buf, curve, r, s) != DROPBEAR_SUCCESS) {
+	if (buf_get_ecdsa_verify_params(buf, r, s) != DROPBEAR_SUCCESS) {
 		goto out;
 	}
 
diff --git a/ecdsa.h b/ecdsa.h
index 316235f..5186fb7 100644
--- a/ecdsa.h
+++ b/ecdsa.h
@@ -7,6 +7,7 @@
 
 #ifdef DROPBEAR_ECDSA
 
+/* Prefer the larger size - it's fast anyway */
 #if defined(DROPBEAR_ECC_521)
 #define ECDSA_DEFAULT_SIZE 521
 #elif defined(DROPBEAR_ECC_384)
@@ -26,6 +27,8 @@ enum signkey_type ecdsa_signkey_type(ecc_key * key);
 
 void buf_put_ecdsa_sign(buffer *buf, ecc_key *key, buffer *data_buf);
 int buf_ecdsa_verify(buffer *buf, ecc_key *key, buffer *data_buf);
+/* Returns 1 on success */
+int signkey_is_ecdsa(enum signkey_type type);
 
 #endif
 
diff --git a/gensignkey.c b/gensignkey.c
new file mode 100644
index 0000000..88a3949
--- /dev/null
+++ b/gensignkey.c
@@ -0,0 +1,131 @@
+#include "includes.h"
+#include "dbutil.h"
+#include "buffer.h"
+#include "ecdsa.h"
+#include "genrsa.h"
+#include "gendss.h"
+#include "signkey.h"
+
+#define RSA_DEFAULT_SIZE 2048
+#define DSS_DEFAULT_SIZE 1024
+
+// Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE
+static int buf_writefile(buffer * buf, const char * filename) {
+	int ret = DROPBEAR_FAILURE;
+	int fd = -1;
+
+	fd = open(filename, O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
+	if (fd < 0) {
+		dropbear_log(LOG_ERR, "Couldn't create new file %s: %s",
+			filename, strerror(errno));
+		goto out;
+	}
+
+	/* write the file now */
+	while (buf->pos != buf->len) {
+		int len = write(fd, buf_getptr(buf, buf->len - buf->pos),
+				buf->len - buf->pos);
+		if (errno == EINTR) {
+			continue;
+		}
+		if (len <= 0) {
+			dropbear_log(LOG_ERR, "Failed writing file %s: %s",
+				filename, strerror(errno));
+			goto out;
+		}
+		buf_incrpos(buf, len);
+	}
+
+	ret = DROPBEAR_SUCCESS;
+
+out:
+	if (fd >= 0) {
+		m_close(fd);
+	}
+	return ret;
+}
+
+/* returns 0 on failure */
+static int get_default_bits(enum signkey_type keytype)
+{
+        switch (keytype) {
+#ifdef DROPBEAR_RSA
+            case DROPBEAR_SIGNKEY_RSA:
+				return RSA_DEFAULT_SIZE;
+#endif
+#ifdef DROPBEAR_DSS
+            case DROPBEAR_SIGNKEY_DSS:
+                return DSS_DEFAULT_SIZE;
+#endif
+#ifdef DROPBEAR_ECDSA
+            case DROPBEAR_SIGNKEY_ECDSA_KEYGEN:
+                return ECDSA_DEFAULT_SIZE;
+            case DROPBEAR_SIGNKEY_ECDSA_NISTP521:
+            	return 521;
+            case DROPBEAR_SIGNKEY_ECDSA_NISTP384:
+            	return 384;
+            case DROPBEAR_SIGNKEY_ECDSA_NISTP256:
+            	return 256;
+#endif
+            default:
+                return 0;
+		}
+}
+
+int signkey_generate(enum signkey_type keytype, int bits, const char* filename)
+{
+	sign_key * key = NULL;
+	buffer *buf = NULL;
+	int ret = DROPBEAR_FAILURE;
+	if (bits == 0)
+	{
+		bits = get_default_bits(keytype);
+	}
+
+	/* now we can generate the key */
+	key = new_sign_key();
+
+	seedrandom();
+
+	switch(keytype) {
+#ifdef DROPBEAR_RSA
+		case DROPBEAR_SIGNKEY_RSA:
+			key->rsakey = gen_rsa_priv_key(bits);
+			break;
+#endif
+#ifdef DROPBEAR_DSS
+		case DROPBEAR_SIGNKEY_DSS:
+			key->dsskey = gen_dss_priv_key(bits);
+			break;
+#endif
+#ifdef DROPBEAR_ECDSA
+		case DROPBEAR_SIGNKEY_ECDSA_KEYGEN:
+		case DROPBEAR_SIGNKEY_ECDSA_NISTP521:
+		case DROPBEAR_SIGNKEY_ECDSA_NISTP384:
+		case DROPBEAR_SIGNKEY_ECDSA_NISTP256:
+			{
+				ecc_key *ecckey = gen_ecdsa_priv_key(bits);
+				keytype = ecdsa_signkey_type(ecckey);
+				*signkey_key_ptr(key, keytype) = ecckey;
+			}
+			break;
+#endif
+		default:
+			dropbear_exit("Internal error");
+	}
+
+	seedrandom();
+
+	buf = buf_new(MAX_PRIVKEY_SIZE); 
+
+	buf_put_priv_key(buf, key, keytype);
+	sign_key_free(key);
+	key = NULL;
+	buf_setpos(buf, 0);
+	ret = buf_writefile(buf, filename);
+
+	buf_burn(buf);
+	buf_free(buf);
+	buf = NULL;
+	return ret;
+}
diff --git a/gensignkey.h b/gensignkey.h
new file mode 100644
index 0000000..b463a42
--- /dev/null
+++ b/gensignkey.h
@@ -0,0 +1,8 @@
+#ifndef _GENSIGNKEY_H
+#define _GENSIGNKEY_H
+
+#include "signkey.h"
+
+int signkey_generate(enum signkey_type type, int bits, const char* filename);
+
+#endif
diff --git a/kex.h b/kex.h
index e2e186b..144df59 100644
--- a/kex.h
+++ b/kex.h
@@ -47,6 +47,13 @@ void kexecdh_comb_key(struct kex_ecdh_param *param, buffer *pub_them,
 		sign_key *hostkey);
 #endif
 
+#ifdef DROPBEAR_CURVE25519
+struct kex_curve25519_param *gen_kexcurve25519_param();
+void free_kexcurve25519_param(struct kex_curve25519_param *param);
+void kexcurve25519_comb_key(struct kex_curve25519_param *param, buffer *pub_them,
+		sign_key *hostkey);
+#endif
+
 #ifndef DISABLE_ZLIB
 int is_compress_trans();
 int is_compress_recv();
@@ -92,6 +99,18 @@ struct kex_ecdh_param {
 };
 #endif
 
+#ifdef DROPBEAR_CURVE25519
+#define CURVE25519_LEN 32
+struct kex_curve25519_param {
+	unsigned char priv[CURVE25519_LEN];
+	unsigned char pub[CURVE25519_LEN];
+};
+
+/* No header file for curve25519_donna */
+int curve25519_donna(unsigned char *out, const unsigned char *secret, const unsigned char *other);
+#endif
+
+
 #define MAX_KEXHASHBUF 2000
 
 #endif /* _KEX_H_ */
diff --git a/keyimport.c b/keyimport.c
index f3fe96a..7098ae7 100644
--- a/keyimport.c
+++ b/keyimport.c
@@ -112,7 +112,7 @@ static sign_key *dropbear_read(const char* filename) {
 
 	buffer * buf = NULL;
 	sign_key *ret = NULL;
-	int type;
+	enum signkey_type type;
 
 	buf = buf_new(MAX_PRIVKEY_SIZE);
 	if (buf_readfile(buf, filename) == DROPBEAR_FAILURE) {
@@ -501,7 +501,7 @@ static int openssh_encrypted(const char *filename)
 	return ret;
 }
 
-static sign_key *openssh_read(const char *filename, char *passphrase)
+static sign_key *openssh_read(const char *filename, char * UNUSED(passphrase))
 {
 	struct openssh_key *key;
 	unsigned char *p;
@@ -511,7 +511,7 @@ static sign_key *openssh_read(const char *filename, char *passphrase)
 	char *errmsg;
 	char *modptr = NULL;
 	int modlen = -9999;
-	int type;
+	enum signkey_type type;
 
 	sign_key *retkey;
 	buffer * blobbuf = NULL;
@@ -709,19 +709,29 @@ static sign_key *openssh_read(const char *filename, char *passphrase)
 			goto error;
 		}
 
-		if (len == sizeof(OID_SEC256R1_BLOB) 
+		if (0) {}
+#ifdef DROPBEAR_ECC_256
+		else if (len == sizeof(OID_SEC256R1_BLOB) 
 			&& memcmp(p, OID_SEC256R1_BLOB, len) == 0) {
 			retkey->type = DROPBEAR_SIGNKEY_ECDSA_NISTP256;
 			curve = &ecc_curve_nistp256;
-		} else if (len == sizeof(OID_SEC384R1_BLOB)
+		} 
+#endif
+#ifdef DROPBEAR_ECC_384
+		else if (len == sizeof(OID_SEC384R1_BLOB)
 			&& memcmp(p, OID_SEC384R1_BLOB, len) == 0) {
 			retkey->type = DROPBEAR_SIGNKEY_ECDSA_NISTP384;
 			curve = &ecc_curve_nistp384;
-		} else if (len == sizeof(OID_SEC521R1_BLOB)
+		} 
+#endif
+#ifdef DROPBEAR_ECC_521
+		else if (len == sizeof(OID_SEC521R1_BLOB)
 			&& memcmp(p, OID_SEC521R1_BLOB, len) == 0) {
 			retkey->type = DROPBEAR_SIGNKEY_ECDSA_NISTP521;
 			curve = &ecc_curve_nistp521;
-		} else {
+		} 
+#endif
+		else {
 			errmsg = "Unknown ECC key type";
 			goto error;
 		}
@@ -1018,8 +1028,8 @@ static int openssh_write(const char *filename, sign_key *key,
 		}
 		*/
 		buffer *seq_buf = buf_new(400);
-		ecc_key **eck = signkey_ecc_key_ptr(key, key->type);
-		const unsigned long curve_size = (*eck)->dp->size;
+		ecc_key **eck = (ecc_key**)signkey_key_ptr(key, key->type);
+		const long curve_size = (*eck)->dp->size;
 		int curve_oid_len = 0;
 		const void* curve_oid = NULL;
 		unsigned long pubkey_size = 2*curve_size+1;
diff --git a/options.h b/options.h
index 8109dd3..726e64c 100644
--- a/options.h
+++ b/options.h
@@ -8,7 +8,7 @@
 /* Define compile-time options below - the "#ifndef DROPBEAR_XXX .... #endif"
  * parts are to allow for commandline -DDROPBEAR_XXX options etc. */
 
-/* Important: Many options will require "make clean" after changes */
+/* IMPORTANT: Many options will require "make clean" after changes */
 
 #ifndef DROPBEAR_DEFPORT
 #define DROPBEAR_DEFPORT "22"
@@ -129,7 +129,7 @@ much traffic. */
 
 /* You can also disable integrity. Don't bother disabling this if you're
  * still using a cipher, it's relatively cheap. If you disable this it's dead
- * simple to run arbitrary commands on the remote host. Beware. */
+ * simple for an attacker to run arbitrary commands on the remote host. Beware. */
 /* #define DROPBEAR_NONE_INTEGRITY */
 
 /* Hostkey/public key algorithms - at least one required, these are used
@@ -138,14 +138,26 @@ much traffic. */
  * SSH2 RFC Draft requires dss, recommends rsa */
 #define DROPBEAR_RSA
 #define DROPBEAR_DSS
-
-#define DROPBEAR_ECDH
+/* ECDSA is significantly faster than RSA or DSS. Compiling in ECC
+ * code (either ECDSA or ECDH) increases binary size - around 30kB
+ * on x86-64 */
 #define DROPBEAR_ECDSA
 
-/* RSA can be vulnerable to timing attacks which use the time required for
- * signing to guess the private key. Blinding avoids this attack, though makes
- * signing operations slightly slower. */
-#define RSA_BLINDING
+/* Generate hostkeys as-needed when the first connection using that key type occurs.
+   This avoids the need to otherwise run "dropbearkey" and avoids some problems
+   with badly seeded /dev/urandom when systems first boot.
+   This also requires a runtime flag "-R". This adds ~4kB to binary size (or hardly 
+   anything if dropbearkey is linked in a "dropbearmulti" binary) */
+#define DROPBEAR_DELAY_HOSTKEY
+
+/* Enable Curve25519 for key exchange. This is another elliptic
+ * curve method with good security properties. Increases binary size
+ * by ~8kB on x86-64 */
+#define DROPBEAR_CURVE25519
+
+/* Enable elliptic curve Diffie Hellman key exchange, see note about
+ * ECDSA above */
+#define DROPBEAR_ECDH
 
 /* Control the memory/performance/compression tradeoff for zlib.
  * Set windowBits=8 for least memory usage, see your system's
@@ -182,7 +194,7 @@ much traffic. */
 
 #define ENABLE_SVR_PASSWORD_AUTH
 /* PAM requires ./configure --enable-pam */
-//#define ENABLE_SVR_PAM_AUTH
+/*#define ENABLE_SVR_PAM_AUTH */
 #define ENABLE_SVR_PUBKEY_AUTH
 
 /* Whether to take public key options in 
diff --git a/runopts.h b/runopts.h
index 59e968a..21fc8e5 100644
--- a/runopts.h
+++ b/runopts.h
@@ -100,6 +100,8 @@ typedef struct svr_runopts {
 
 	sign_key *hostkey;
 
+	int delay_hostkey;
+
 	char *hostkey_files[MAX_HOSTKEYS];
 	int num_hostkey_files;
 
diff --git a/session.h b/session.h
index 7d7724c..88eb309 100644
--- a/session.h
+++ b/session.h
@@ -244,6 +244,7 @@ struct clientsession {
 	// XXX - move these to kexstate?
 	struct kex_dh_param *dh_param;
 	struct kex_ecdh_param *ecdh_param;
+	struct kex_curve25519_param *curve25519_param;
 	const struct dropbear_kex *param_kex_algo; /* KEX algorithm corresponding to current dh_e and dh_x */
 
 	cli_kex_state kex_state; /* Used for progressing KEX */
diff --git a/signkey.c b/signkey.c
index 0d08f10..b1e0220 100644
--- a/signkey.c
+++ b/signkey.c
@@ -39,8 +39,7 @@ static const char *signkey_names[DROPBEAR_SIGNKEY_NUM_NAMED] = {
 #ifdef DROPBEAR_ECDSA
 	"ecdsa-sha2-nistp256",
 	"ecdsa-sha2-nistp384",
-	"ecdsa-sha2-nistp521",
-	"ecdsa" // for keygen
+	"ecdsa-sha2-nistp521"
 #endif // DROPBEAR_ECDSA
 };
 
@@ -181,7 +180,7 @@ int buf_get_pub_key(buffer *buf, sign_key *key, enum signkey_type *type) {
 	}
 #endif
 #ifdef DROPBEAR_ECDSA
-	{
+	if (signkey_is_ecdsa(keytype)) {
 		ecc_key **eck = (ecc_key**)signkey_key_ptr(key, keytype);
 		if (eck) {
 			if (*eck) {
@@ -249,7 +248,7 @@ int buf_get_priv_key(buffer *buf, sign_key *key, enum signkey_type *type) {
 	}
 #endif
 #ifdef DROPBEAR_ECDSA
-	{
+	if (signkey_is_ecdsa(keytype)) {
 		ecc_key **eck = (ecc_key**)signkey_key_ptr(key, keytype);
 		if (eck) {
 			if (*eck) {
@@ -289,10 +288,7 @@ void buf_put_pub_key(buffer* buf, sign_key *key, enum signkey_type type) {
 	}
 #endif
 #ifdef DROPBEAR_ECDSA
-	if (type == DROPBEAR_SIGNKEY_ECDSA_NISTP256
-		|| type == DROPBEAR_SIGNKEY_ECDSA_NISTP384
-		|| type == DROPBEAR_SIGNKEY_ECDSA_NISTP521)
-	{
+	if (signkey_is_ecdsa(type)) {
 		ecc_key **eck = (ecc_key**)signkey_key_ptr(key, type);
 		if (eck) {
 			buf_put_ecdsa_pub_key(pubkeys, *eck);
@@ -329,7 +325,7 @@ void buf_put_priv_key(buffer* buf, sign_key *key, enum signkey_type type) {
 	}
 #endif
 #ifdef DROPBEAR_ECDSA
-	{
+	if (signkey_is_ecdsa(type)) {
 		ecc_key **eck = (ecc_key**)signkey_key_ptr(key, type);
 		if (eck) {
 			buf_put_ecdsa_priv_key(buf, *eck);
@@ -354,19 +350,25 @@ void sign_key_free(sign_key *key) {
 	key->rsakey = NULL;
 #endif
 #ifdef DROPBEAR_ECDSA
+#ifdef DROPBEAR_ECC_256
 	if (key->ecckey256) {
 		ecc_free(key->ecckey256);
 		key->ecckey256 = NULL;
 	}
+#endif
+#ifdef DROPBEAR_ECC_384
 	if (key->ecckey384) {
 		ecc_free(key->ecckey384);
 		key->ecckey384 = NULL;
 	}
+#endif
+#ifdef DROPBEAR_ECC_521
 	if (key->ecckey521) {
 		ecc_free(key->ecckey521);
 		key->ecckey521 = NULL;
 	}
 #endif
+#endif
 
 	m_free(key->filename);
 
@@ -484,7 +486,7 @@ void buf_put_sign(buffer* buf, sign_key *key, enum signkey_type type,
 	}
 #endif
 #ifdef DROPBEAR_ECDSA
-	{
+	if (signkey_is_ecdsa(type)) {
 		ecc_key **eck = (ecc_key**)signkey_key_ptr(key, type);
 		if (eck) {
 			buf_put_ecdsa_sign(sigblob, *eck, data_buf);
@@ -535,7 +537,7 @@ int buf_verify(buffer * buf, sign_key *key, buffer *data_buf) {
 	}
 #endif
 #ifdef DROPBEAR_ECDSA
-	{
+	if (signkey_is_ecdsa(type)) {
 		ecc_key **eck = (ecc_key**)signkey_key_ptr(key, type);
 		if (eck) {
 			return buf_ecdsa_verify(buf, *eck, data_buf);
diff --git a/svr-auth.c b/svr-auth.c
index 8666108..2a3ef0e 100644
--- a/svr-auth.c
+++ b/svr-auth.c
@@ -231,7 +231,7 @@ static int checkusername(unsigned char *username, unsigned int userlen) {
 
 	char* listshell = NULL;
 	char* usershell = NULL;
-	int   uid;
+	uid_t uid;
 	TRACE(("enter checkusername"))
 	if (userlen > MAX_USERNAME_LEN) {
 		return DROPBEAR_FAILURE;
diff --git a/svr-authpubkey.c b/svr-authpubkey.c
index e0727de..66fe5e5 100644
--- a/svr-authpubkey.c
+++ b/svr-authpubkey.c
@@ -89,7 +89,7 @@ void svr_auth_pubkey() {
 	buffer * signbuf = NULL;
 	sign_key * key = NULL;
 	char* fp = NULL;
-	int type = -1;
+	enum signkey_type type = -1;
 
 	TRACE(("enter pubkeyauth"))
 
@@ -294,8 +294,8 @@ static int checkpubkey(unsigned char* algo, unsigned int algolen,
 			options_buf = buf_new(options_len);
 			buf_putbytes(options_buf, options_start, options_len);
 
-			/* compare the algorithm */
-			if (line->pos + algolen > line->len) {
+			/* compare the algorithm. +3 so we have enough bytes to read a space and some base64 characters too. */
+			if (line->pos + algolen+3 > line->len) {
 				continue;
 			}
 			if (strncmp(buf_getptr(line, algolen), algo, algolen) != 0) { 
diff --git a/svr-kex.c b/svr-kex.c
index 664ae84..629a31b 100644
--- a/svr-kex.c
+++ b/svr-kex.c
@@ -35,6 +35,7 @@
 #include "random.h"
 #include "runopts.h"
 #include "ecc.h"
+#include "gensignkey.h"
 
 static void send_msg_kexdh_reply(mp_int *dh_e, buffer *ecdh_qs);
 
@@ -52,15 +53,22 @@ void recv_msg_kexdh_init() {
 		dropbear_exit("Premature kexdh_init message received");
 	}
 
-	if (IS_NORMAL_DH(ses.newkeys->algo_kex)) {
-		m_mp_init(&dh_e);
-		if (buf_getmpint(ses.payload, &dh_e) != DROPBEAR_SUCCESS) {
-			dropbear_exit("Failed to get kex value");
-		}
-	} else {
-#ifdef DROPBEAR_ECDH
-		ecdh_qs = buf_getstringbuf(ses.payload);
+	switch (ses.newkeys->algo_kex->mode) {
+		case DROPBEAR_KEX_NORMAL_DH:
+			m_mp_init(&dh_e);
+			if (buf_getmpint(ses.payload, &dh_e) != DROPBEAR_SUCCESS) {
+				dropbear_exit("Bad kex value");
+			}
+			break;
+		case DROPBEAR_KEX_ECDH:
+		case DROPBEAR_KEX_CURVE25519:
+#if defined(DROPBEAR_ECDH) || defined(DROPBEAR_CURVE25519)
+			ecdh_qs = buf_getstringbuf(ses.payload);
 #endif
+			break;
+	}
+	if (ses.payload->pos != ses.payload->len) {
+		dropbear_exit("Bad kex value");
 	}
 
 	send_msg_kexdh_reply(&dh_e, ecdh_qs);
@@ -68,6 +76,7 @@ void recv_msg_kexdh_init() {
 	mp_clear(&dh_e);
 	if (ecdh_qs) {
 		buf_free(ecdh_qs);
+		ecdh_qs = NULL;
 	}
 
 	send_msg_newkeys();
@@ -75,6 +84,79 @@ void recv_msg_kexdh_init() {
 	ses.requirenext[1] = 0;
 	TRACE(("leave recv_msg_kexdh_init"))
 }
+
+#ifdef DROPBEAR_DELAY_HOSTKEY
+static void svr_ensure_hostkey() {
+
+	const char* fn = NULL;
+	char *fn_temp = NULL;
+	enum signkey_type type = ses.newkeys->algo_hostkey;
+	void **hostkey = signkey_key_ptr(svr_opts.hostkey, type);
+	int ret = DROPBEAR_FAILURE;
+
+	if (hostkey && *hostkey) {
+		return;
+	}
+
+	switch (type)
+	{
+#ifdef DROPBEAR_RSA
+		case DROPBEAR_SIGNKEY_RSA:
+			fn = RSA_PRIV_FILENAME;
+			break;
+#endif
+#ifdef DROPBEAR_DSS
+		case DROPBEAR_SIGNKEY_DSS:
+			fn = DSS_PRIV_FILENAME;
+			break;
+#endif
+#ifdef DROPBEAR_ECDSA
+		case DROPBEAR_SIGNKEY_ECDSA_NISTP256:
+		case DROPBEAR_SIGNKEY_ECDSA_NISTP384:
+		case DROPBEAR_SIGNKEY_ECDSA_NISTP521:
+			fn = ECDSA_PRIV_FILENAME;
+			break;
+#endif
+		default:
+			(void)0;
+	}
+
+	if (readhostkey(fn, svr_opts.hostkey, &type) == DROPBEAR_SUCCESS) {
+		return;
+	}
+
+	fn_temp = m_malloc(strlen(fn) + 20);
+	snprintf(fn_temp, strlen(fn)+20, "%s.tmp%d", fn, getpid());
+
+	if (signkey_generate(type, 0, fn_temp) == DROPBEAR_FAILURE) {
+		goto out;
+	}
+
+	if (link(fn_temp, fn) < 0) {
+		/* It's OK to get EEXIST - we probably just lost a race
+		with another connection to generate the key */
+		if (errno != EEXIST) {
+			dropbear_log(LOG_ERR, "Failed moving key file to %s: %s", fn,
+				strerror(errno));
+			/* XXX fallback to non-atomic copy for some filesystems? */
+			goto out;
+		}
+	}
+
+	ret = readhostkey(fn, svr_opts.hostkey, &type);
+
+out:
+	if (fn_temp) {
+		unlink(fn_temp);
+		m_free(fn_temp);
+	}
+
+	if (ret == DROPBEAR_FAILURE)
+	{
+		dropbear_exit("Couldn't read or generate hostkey %s", fn);
+	}
+}
+#endif
 	
 /* Generate our side of the diffie-hellman key exchange value (dh_f), and
  * calculate the session key using the diffie-hellman algorithm. Following
@@ -88,26 +170,50 @@ static void send_msg_kexdh_reply(mp_int *dh_e, buffer *ecdh_qs) {
 
 	/* we can start creating the kexdh_reply packet */
 	CHECKCLEARTOWRITE();
+
+#ifdef DROPBEAR_DELAY_HOSTKEY
+	if (svr_opts.delay_hostkey)
+	{
+		svr_ensure_hostkey();
+	}
+#endif
+
 	buf_putbyte(ses.writepayload, SSH_MSG_KEXDH_REPLY);
 	buf_put_pub_key(ses.writepayload, svr_opts.hostkey,
 			ses.newkeys->algo_hostkey);
 
-	if (IS_NORMAL_DH(ses.newkeys->algo_kex)) {
-		// Normal diffie-hellman
-		struct kex_dh_param * dh_param = gen_kexdh_param();
-		kexdh_comb_key(dh_param, dh_e, svr_opts.hostkey);
-
-		/* put f */
-		buf_putmpint(ses.writepayload, &dh_param->pub);
-		free_kexdh_param(dh_param);
-	} else {
+	switch (ses.newkeys->algo_kex->mode) {
+		case DROPBEAR_KEX_NORMAL_DH:
+			{
+			struct kex_dh_param * dh_param = gen_kexdh_param();
+			kexdh_comb_key(dh_param, dh_e, svr_opts.hostkey);
+
+			/* put f */
+			buf_putmpint(ses.writepayload, &dh_param->pub);
+			free_kexdh_param(dh_param);
+			}
+			break;
+		case DROPBEAR_KEX_ECDH:
 #ifdef DROPBEAR_ECDH
-		struct kex_ecdh_param *ecdh_param = gen_kexecdh_param();
-		kexecdh_comb_key(ecdh_param, ecdh_qs, svr_opts.hostkey);
+			{
+			struct kex_ecdh_param *ecdh_param = gen_kexecdh_param();
+			kexecdh_comb_key(ecdh_param, ecdh_qs, svr_opts.hostkey);
 
-		buf_put_ecc_raw_pubkey_string(ses.writepayload, &ecdh_param->key);
-		free_kexecdh_param(ecdh_param);
+			buf_put_ecc_raw_pubkey_string(ses.writepayload, &ecdh_param->key);
+			free_kexecdh_param(ecdh_param);
+			}
+#endif
+			break;
+		case DROPBEAR_KEX_CURVE25519:
+#ifdef DROPBEAR_CURVE25519
+			{
+			struct kex_curve25519_param *param = gen_kexcurve25519_param();
+			kexcurve25519_comb_key(param, ecdh_qs, svr_opts.hostkey);
+			buf_putstring(ses.writepayload, param->pub, CURVE25519_LEN);
+			free_kexcurve25519_param(param);
+			}
 #endif
+			break;
 	}
 
 	/* calc the signature */
diff --git a/svr-runopts.c b/svr-runopts.c
index 2db88c2..cbfd190 100644
--- a/svr-runopts.c
+++ b/svr-runopts.c
@@ -44,13 +44,19 @@ static void printhelp(const char * progname) {
 					"-b bannerfile	Display the contents of bannerfile"
 					" before user login\n"
 					"		(default: none)\n"
+					"-r keyfile  Specify hostkeys (repeatable)\n"
+					"		defaults: \n"
 #ifdef DROPBEAR_DSS
-					"-d dsskeyfile	Use dsskeyfile for the DSS host key\n"
-					"		(default: %s)\n"
+					"		dss %s\n"
 #endif
 #ifdef DROPBEAR_RSA
-					"-r rsakeyfile	Use rsakeyfile for the RSA host key\n"
-					"		(default: %s)\n"
+					"		rsa %s\n"
+#endif
+#ifdef DROPBEAR_ECDSA
+					"		ecdsa %s\n"
+#endif
+#ifdef DROPBEAR_DELAY_HOSTKEY
+					"-R		Create hostkeys as required\n" 
 #endif
 					"-F		Don't fork into background\n"
 #ifdef DISABLE_SYSLOG
@@ -96,6 +102,9 @@ static void printhelp(const char * progname) {
 #ifdef DROPBEAR_RSA
 					RSA_PRIV_FILENAME,
 #endif
+#ifdef DROPBEAR_ECDSA
+					ECDSA_PRIV_FILENAME,
+#endif
 					DROPBEAR_MAX_PORTS, DROPBEAR_DEFPORT, DROPBEAR_PIDFILE,
 					DEFAULT_RECV_WINDOW, DEFAULT_KEEPALIVE, DEFAULT_IDLE_TIMEOUT);
 }
@@ -122,6 +131,7 @@ void svr_getopts(int argc, char ** argv) {
 	svr_opts.inetdmode = 0;
 	svr_opts.portcount = 0;
 	svr_opts.hostkey = NULL;
+	svr_opts.delay_hostkey = 0;
 	svr_opts.pidfile = DROPBEAR_PIDFILE;
 #ifdef ENABLE_SVR_LOCALTCPFWD
 	svr_opts.nolocaltcp = 0;
@@ -180,6 +190,9 @@ void svr_getopts(int argc, char ** argv) {
 				case 'r':
 					next = &keyfile;
 					break;
+				case 'R':
+					svr_opts.delay_hostkey = 1;
+					break;
 				case 'F':
 					svr_opts.forkbg = 0;
 					break;
@@ -390,37 +403,37 @@ static void loadhostkey_helper(const char *name, void** src, void** dst, int fat
 /* Must be called after syslog/etc is working */
 static void loadhostkey(const char *keyfile, int fatal_duplicate) {
 	sign_key * read_key = new_sign_key();
-	int type = DROPBEAR_SIGNKEY_ANY;
+	enum signkey_type type = DROPBEAR_SIGNKEY_ANY;
 	if (readhostkey(keyfile, read_key, &type) == DROPBEAR_FAILURE) {
 		dropbear_log(LOG_WARNING, "Failed loading %s", keyfile);
 	}
 
 #ifdef DROPBEAR_RSA
 	if (type == DROPBEAR_SIGNKEY_RSA) {
-		loadhostkey_helper("RSA", &read_key->rsakey, &svr_opts.hostkey->rsakey, fatal_duplicate);
+		loadhostkey_helper("RSA", (void**)&read_key->rsakey, (void**)&svr_opts.hostkey->rsakey, fatal_duplicate);
 	}
 #endif
 
 #ifdef DROPBEAR_DSS
 	if (type == DROPBEAR_SIGNKEY_DSS) {
-		loadhostkey_helper("DSS", &read_key->dsskey, &svr_opts.hostkey->dsskey, fatal_duplicate);
+		loadhostkey_helper("DSS", (void**)&read_key->dsskey, (void**)&svr_opts.hostkey->dsskey, fatal_duplicate);
 	}
 #endif
 
 #ifdef DROPBEAR_ECDSA
 #ifdef DROPBEAR_ECC_256
 	if (type == DROPBEAR_SIGNKEY_ECDSA_NISTP256) {
-		loadhostkey_helper("ECDSA256", &read_key->ecckey256, &svr_opts.hostkey->ecckey256, fatal_duplicate);
+		loadhostkey_helper("ECDSA256", (void**)&read_key->ecckey256, (void**)&svr_opts.hostkey->ecckey256, fatal_duplicate);
 	}
 #endif
 #ifdef DROPBEAR_ECC_384
 	if (type == DROPBEAR_SIGNKEY_ECDSA_NISTP384) {
-		loadhostkey_helper("ECDSA384", &read_key->ecckey384, &svr_opts.hostkey->ecckey384, fatal_duplicate);
+		loadhostkey_helper("ECDSA384", (void**)&read_key->ecckey384, (void**)&svr_opts.hostkey->ecckey384, fatal_duplicate);
 	}
 #endif
 #ifdef DROPBEAR_ECC_521
 	if (type == DROPBEAR_SIGNKEY_ECDSA_NISTP521) {
-		loadhostkey_helper("ECDSA521", &read_key->ecckey521, &svr_opts.hostkey->ecckey521, fatal_duplicate);
+		loadhostkey_helper("ECDSA521", (void**)&read_key->ecckey521, (void**)&svr_opts.hostkey->ecckey521, fatal_duplicate);
 	}
 #endif
 #endif // DROPBEAR_ECDSA
@@ -438,6 +451,7 @@ static void addhostkey(const char *keyfile) {
 
 void load_all_hostkeys() {
 	int i;
+	int disable_unset_keys = 1;
 
 	svr_opts.hostkey = new_sign_key();
 
@@ -459,31 +473,47 @@ void load_all_hostkeys() {
 	loadhostkey(ECDSA_PRIV_FILENAME, 0);
 #endif
 
+#ifdef DROPBEAR_DELAY_HOSTKEY
+	if (svr_opts.delay_hostkey)
+	{
+		disable_unset_keys = 0;
+	}
+#endif
+
 #ifdef DROPBEAR_RSA
-	if (!svr_opts.hostkey->rsakey) {
+	if (disable_unset_keys && !svr_opts.hostkey->rsakey) {
 		disablekey(DROPBEAR_SIGNKEY_RSA);
 	}
 #endif
+
 #ifdef DROPBEAR_DSS
-	if (!svr_opts.hostkey->dsskey) {
+	if (disable_unset_keys && !svr_opts.hostkey->dsskey) {
 		disablekey(DROPBEAR_SIGNKEY_RSA);
 	}
 #endif
+
+
 #ifdef DROPBEAR_ECDSA
 #ifdef DROPBEAR_ECC_256
-	if (!svr_opts.hostkey->ecckey256) {
+	if ((disable_unset_keys || ECDSA_DEFAULT_SIZE != 256)
+		&& !svr_opts.hostkey->ecckey256) {
 		disablekey(DROPBEAR_SIGNKEY_ECDSA_NISTP256);
 	}
 #endif
+
 #ifdef DROPBEAR_ECC_384
-	if (!svr_opts.hostkey->ecckey384) {
+	if ((disable_unset_keys || ECDSA_DEFAULT_SIZE != 384)
+		&& !svr_opts.hostkey->ecckey384) {
 		disablekey(DROPBEAR_SIGNKEY_ECDSA_NISTP384);
 	}
 #endif
+
 #ifdef DROPBEAR_ECC_521
-	if (!svr_opts.hostkey->ecckey521) {
+	if ((disable_unset_keys || ECDSA_DEFAULT_SIZE != 521)
+		&& !svr_opts.hostkey->ecckey521) {
 		disablekey(DROPBEAR_SIGNKEY_ECDSA_NISTP521);
 	}
 #endif
-#endif
+#endif /* DROPBEAR_ECDSA */
+
 }
diff --git a/sysoptions.h b/sysoptions.h
index 8d57375..8459eb6 100644
--- a/sysoptions.h
+++ b/sysoptions.h
@@ -104,21 +104,27 @@
 #define DROPBEAR_LTC_PRNG
 #endif
 
-// hashes which will be linked and registered
-#if defined(DROPBEAR_SHA2_256_HMAC) || defined(DROPBEAR_ECC_256)
+/* RSA can be vulnerable to timing attacks which use the time required for
+ * signing to guess the private key. Blinding avoids this attack, though makes
+ * signing operations slightly slower. */
+#define RSA_BLINDING
+
+/* hashes which will be linked and registered */
+#if defined(DROPBEAR_SHA2_256_HMAC) || defined(DROPBEAR_ECC_256) || defined(DROPBEAR_CURVE25519)
 #define DROPBEAR_SHA256
 #endif
 #if defined(DROPBEAR_ECC_384)
 #define DROPBEAR_SHA384
 #endif
-#if defined(DROPBEAR_SHA2_512_HMAC) || defined(DROPBEAR_ECC_521)
+/* LTC SHA384 depends on SHA512 */
+#if defined(DROPBEAR_SHA2_512_HMAC) || defined(DROPBEAR_ECC_521) || defined(DROPBEAR_ECC_384)
 #define DROPBEAR_SHA512
 #endif
 #if defined(DROPBEAR_MD5_HMAC)
 #define DROPBEAR_MD5
 #endif
 
-// roughly 2x 521 bits
+/* roughly 2x 521 bits */
 #define MAX_ECC_SIZE 140
 
 #define MAX_NAME_LEN 64 /* maximum length of a protocol name, isn't