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, 72 insertions, 0 deletions

diff --git a/fuzzer-kexcurve25519.c b/fuzzer-kexcurve25519.c
new file mode 100644
index 0000000..f2eab14
--- /dev/null
+++ b/fuzzer-kexcurve25519.c
@@ -0,0 +1,72 @@
+#include "fuzz.h"
+#include "session.h"
+#include "fuzz-wrapfd.h"
+#include "debug.h"
+#include "runopts.h"
+#include "algo.h"
+#include "bignum.h"
+
+int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+	static int once = 0;
+	static struct key_context* keep_newkeys = NULL;
+	/* number of generated parameters is limited by the timeout for the first run.
+	   TODO move this to the libfuzzer initialiser function instead if the timeout
+	   doesn't apply there */
+	#define NUM_PARAMS 20
+	static struct kex_curve25519_param *curve25519_params[NUM_PARAMS];
+
+	if (!once) {
+		fuzz_common_setup();
+		fuzz_svr_setup();
+
+		keep_newkeys = (struct key_context*)m_malloc(sizeof(struct key_context));
+		keep_newkeys->algo_kex = fuzz_get_algo(sshkex, "curve25519-sha256");
+		keep_newkeys->algo_hostkey = DROPBEAR_SIGNKEY_ED25519;
+		ses.newkeys = keep_newkeys;
+
+		/* Pre-generate parameters */
+		int i;
+		for (i = 0; i < NUM_PARAMS; i++) {
+			curve25519_params[i] = gen_kexcurve25519_param();
+		}
+
+		once = 1;
+	}
+
+	if (fuzz_set_input(Data, Size) == DROPBEAR_FAILURE) {
+		return 0;
+	}
+
+	m_malloc_set_epoch(1);
+
+	if (setjmp(fuzz.jmp) == 0) {
+		/* Based on recv_msg_kexdh_init()/send_msg_kexdh_reply() 
+		with DROPBEAR_KEX_CURVE25519 */
+		ses.newkeys = keep_newkeys;
+
+		/* Choose from the collection of curve25519 params */
+		unsigned int e = buf_getint(fuzz.input);
+		struct kex_curve25519_param *curve25519_param = curve25519_params[e % NUM_PARAMS];
+
+		buffer * ecdh_qs = buf_getstringbuf(fuzz.input);
+
+		ses.kexhashbuf = buf_new(KEXHASHBUF_MAX_INTS);
+		kexcurve25519_comb_key(curve25519_param, ecdh_qs, svr_opts.hostkey);
+
+		mp_clear(ses.dh_K);
+		m_free(ses.dh_K);
+		buf_free(ecdh_qs);
+
+		buf_free(ses.hash);
+		buf_free(ses.session_id);
+		/* kexhashbuf is freed in kexdh_comb_key */
+
+		m_malloc_free_epoch(1, 0);
+	} else {
+		m_malloc_free_epoch(1, 1);
+		TRACE(("dropbear_exit longjmped"))
+		/* dropbear_exit jumped here */
+	}
+
+	return 0;
+}