Add Ed25519 support (#91)

* Add support for Ed25519 as a public key type

Ed25519 is a elliptic curve signature scheme that offers
better security than ECDSA and DSA and good performance. It may be
used for both user and host keys.

OpenSSH key import and fuzzer are not supported yet.

Initially inspired by Peter Szabo.

* Add curve25519 and ed25519 fuzzers

* Add import and export of Ed25519 keys

1 files changed, 184 insertions, 0 deletions

diff --git a/ed25519.c b/ed25519.c
new file mode 100644
index 0000000..3fb544c
--- /dev/null
+++ b/ed25519.c
@@ -0,0 +1,184 @@
+/*
+ * Dropbear - a SSH2 server
+ * 
+ * Copyright (c) 2002,2003 Matt Johnston
+ * All rights reserved.
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE. */
+
+/* Perform Ed25519 operations on data, including reading keys, signing and
+ * verification. */
+
+#include "includes.h"
+#include "dbutil.h"
+#include "buffer.h"
+#include "ssh.h"
+#include "curve25519.h"
+#include "ed25519.h"
+
+#if DROPBEAR_ED25519
+
+/* Load a public ed25519 key from a buffer, initialising the values.
+ * The key will have the same format as buf_put_ed25519_key.
+ * These should be freed with ed25519_key_free.
+ * Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
+int buf_get_ed25519_pub_key(buffer *buf, dropbear_ed25519_key *key) {
+
+	unsigned int len;
+
+	TRACE(("enter buf_get_ed25519_pub_key"))
+	dropbear_assert(key != NULL);
+
+	buf_incrpos(buf, 4+SSH_SIGNKEY_ED25519_LEN); /* int + "ssh-ed25519" */
+
+	len = buf_getint(buf);
+	if (len != CURVE25519_LEN || buf->len - buf->pos < len) {
+		TRACE(("leave buf_get_ed25519_pub_key: failure"))
+		return DROPBEAR_FAILURE;
+	}
+
+	m_burn(key->priv, CURVE25519_LEN);
+	memcpy(key->pub, buf_getptr(buf, CURVE25519_LEN), CURVE25519_LEN);
+	buf_incrpos(buf, CURVE25519_LEN);
+
+	TRACE(("leave buf_get_ed25519_pub_key: success"))
+	return DROPBEAR_SUCCESS;
+}
+
+/* Same as buf_get_ed25519_pub_key, but reads private key at the end.
+ * Loads a public and private ed25519 key from a buffer
+ * Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
+int buf_get_ed25519_priv_key(buffer *buf, dropbear_ed25519_key *key) {
+
+	unsigned int len;
+
+	TRACE(("enter buf_get_ed25519_priv_key"))
+	dropbear_assert(key != NULL);
+
+	buf_incrpos(buf, 4+SSH_SIGNKEY_ED25519_LEN); /* int + "ssh-ed25519" */
+
+	len = buf_getint(buf);
+	if (len != CURVE25519_LEN*2 || buf->len - buf->pos < len) {
+		TRACE(("leave buf_get_ed25519_priv_key: failure"))
+		return DROPBEAR_FAILURE;
+	}
+
+	memcpy(key->priv, buf_getptr(buf, CURVE25519_LEN), CURVE25519_LEN);
+	buf_incrpos(buf, CURVE25519_LEN);
+	memcpy(key->pub, buf_getptr(buf, CURVE25519_LEN), CURVE25519_LEN);
+	buf_incrpos(buf, CURVE25519_LEN);
+
+	TRACE(("leave buf_get_ed25519_pub_key: success"))
+	return DROPBEAR_SUCCESS;
+}
+
+/* Clear and free the memory used by a public or private key */
+void ed25519_key_free(dropbear_ed25519_key *key) {
+
+	TRACE2(("enter ed25519_key_free"))
+
+	if (key == NULL) {
+		TRACE2(("leave ed25519_key_free: key == NULL"))
+		return;
+	}
+	m_burn(key->priv, CURVE25519_LEN);
+	m_free(key);
+
+	TRACE2(("leave rsa_key_free"))
+}
+
+/* Put the public ed25519 key into the buffer in the required format */
+void buf_put_ed25519_pub_key(buffer *buf, const dropbear_ed25519_key *key) {
+
+	TRACE(("enter buf_put_ed25519_pub_key"))
+	dropbear_assert(key != NULL);
+
+	buf_putstring(buf, SSH_SIGNKEY_ED25519, SSH_SIGNKEY_ED25519_LEN);
+	buf_putstring(buf, key->pub, CURVE25519_LEN);
+
+	TRACE(("leave buf_put_ed25519_pub_key"))
+}
+
+/* Put the public and private ed25519 key into the buffer in the required format */
+void buf_put_ed25519_priv_key(buffer *buf, const dropbear_ed25519_key *key) {
+
+	TRACE(("enter buf_put_ed25519_priv_key"))
+	dropbear_assert(key != NULL);
+
+	buf_putstring(buf, SSH_SIGNKEY_ED25519, SSH_SIGNKEY_ED25519_LEN);
+	buf_putint(buf, CURVE25519_LEN*2);
+	buf_putbytes(buf, key->priv, CURVE25519_LEN);
+	buf_putbytes(buf, key->pub, CURVE25519_LEN);
+
+	TRACE(("leave buf_put_ed25519_priv_key"))
+}
+
+/* Sign the data presented with key, writing the signature contents
+ * to the buffer */
+void buf_put_ed25519_sign(buffer* buf, const dropbear_ed25519_key *key, const buffer *data_buf) {
+
+	unsigned char s[64];
+	unsigned long slen = sizeof(s);
+
+	TRACE(("enter buf_put_ed25519_sign"))
+	dropbear_assert(key != NULL);
+
+	if (dropbear_ed25519_sign(data_buf->data, data_buf->len,
+				  s, &slen, key->priv, key->pub) == 0) {
+		buf_putstring(buf, SSH_SIGNKEY_ED25519, SSH_SIGNKEY_ED25519_LEN);
+		buf_putstring(buf, s, slen);
+	}
+
+	TRACE(("leave buf_put_ed25519_sign"))
+}
+
+#if DROPBEAR_SIGNKEY_VERIFY
+/* Verify a signature in buf, made on data by the key given.
+ * Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
+int buf_ed25519_verify(buffer *buf, const dropbear_ed25519_key *key, const buffer *data_buf) {
+
+	int ret = DROPBEAR_FAILURE;
+	unsigned char *s;
+	unsigned long slen;
+
+	TRACE(("enter buf_ed25519_verify"))
+	dropbear_assert(key != NULL);
+
+	slen = buf_getint(buf);
+	if (slen != 64 || buf->len - buf->pos < slen) {
+		TRACE(("bad size"))
+		goto out;
+	}
+	s = buf_getptr(buf, slen);
+
+	if (dropbear_ed25519_verify(data_buf->data, data_buf->len,
+				    s, slen, key->pub) == 0) {
+		/* signature is valid */
+		TRACE(("success!"))
+		ret = DROPBEAR_SUCCESS;
+	}
+
+out:
+	TRACE(("leave buf_ed25519_verify: ret %d", ret))
+	return ret;
+}
+
+#endif /* DROPBEAR_SIGNKEY_VERIFY */
+
+#endif /* DROPBEAR_ED25519 */