ECDH/ECDSA compliance fix: these methods vary the hash function they use

(SHA256/384/512) depending on the length of the curve in use. The previous
code incorrectly used SHA256 in all cases.

This fix will cause authentication failure when using 384 or 521-bit curve
keys if one peer hasn't been upgraded and the other has. (256-bit curve
keys work ok). In particular you may need to specify HostkeyAlgorithms
when connecting to a server that has not been upgraded from an upgraded
client.

ok naddy@

7 files changed, 64 insertions, 28 deletions

diff --git a/usr.bin/ssh/kex.c b/usr.bin/ssh/kex.c
index 27774f2d6c8..5ab764083d0 100644
--- a/usr.bin/ssh/kex.c
+++ b/usr.bin/ssh/kex.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kex.c,v 1.84 2010/08/31 11:54:45 djm Exp $ */
+/* $OpenBSD: kex.c,v 1.85 2010/09/09 10:45:45 djm Exp $ */
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
  *
@@ -313,10 +313,10 @@ choose_kex(Kex *k, char *client, char *server)
 	} else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
 		k->kex_type = KEX_DH_GEX_SHA256;
 		k->evp_md = EVP_sha256();
-	} else if (strncmp(k->name, KEX_ECDH_SHA256,
-	    sizeof(KEX_ECDH_SHA256) - 1) == 0) {
+	} else if (strncmp(k->name, KEX_ECDH_SHA2_STEM,
+	    sizeof(KEX_ECDH_SHA2_STEM) - 1) == 0) {
 		k->kex_type = KEX_ECDH_SHA2;
-		k->evp_md = EVP_sha256();
+		k->evp_md = kex_ecdh_name_to_evpmd(k->name);
 	} else
 		fatal("bad kex alg %s", k->name);
 }
diff --git a/usr.bin/ssh/kex.h b/usr.bin/ssh/kex.h
index 8ef7b291ca6..339c56bd99c 100644
--- a/usr.bin/ssh/kex.h
+++ b/usr.bin/ssh/kex.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: kex.h,v 1.50 2010/08/31 11:54:45 djm Exp $ */
+/* $OpenBSD: kex.h,v 1.51 2010/09/09 10:45:45 djm Exp $ */
 
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
@@ -38,7 +38,7 @@
 #define	KEX_DHGEX_SHA256	"diffie-hellman-group-exchange-sha256"
 #define	KEX_RESUME		"resume@appgate.com"
 /* The following represents the family of ECDH methods */
-#define	KEX_ECDH_SHA256		"ecdh-sha2-"
+#define	KEX_ECDH_SHA2_STEM	"ecdh-sha2-"
 
 #define COMP_NONE	0
 #define COMP_ZLIB	1
@@ -164,6 +164,7 @@ kex_ecdh_hash(const EVP_MD *, const EC_GROUP *, char *, char *, char *, int,
     const BIGNUM *, u_char **, u_int *);
 
 int	kex_ecdh_name_to_nid(const char *);
+const EVP_MD *kex_ecdh_name_to_evpmd(const char *);
 
 void
 derive_ssh1_session_id(BIGNUM *, BIGNUM *, u_int8_t[8], u_int8_t[16]);
diff --git a/usr.bin/ssh/kexecdh.c b/usr.bin/ssh/kexecdh.c
index a5a14f4bdc9..2e31b86cd52 100644
--- a/usr.bin/ssh/kexecdh.c
+++ b/usr.bin/ssh/kexecdh.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kexecdh.c,v 1.1 2010/08/31 11:54:45 djm Exp $ */
+/* $OpenBSD: kexecdh.c,v 1.2 2010/09/09 10:45:45 djm Exp $ */
 /*
  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
  * Copyright (c) 2010 Damien Miller.  All rights reserved.
@@ -46,15 +46,23 @@ kex_ecdh_name_to_nid(const char *kexname)
 {
 	int ret;
 
-	if (strlen(kexname) < sizeof(KEX_ECDH_SHA256) - 1)
+	if (strlen(kexname) < sizeof(KEX_ECDH_SHA2_STEM) - 1)
 		fatal("%s: kexname too short \"%s\"", __func__, kexname);
-	ret = key_curve_name_to_nid(kexname + sizeof(KEX_ECDH_SHA256) - 1);
+	ret = key_curve_name_to_nid(kexname + sizeof(KEX_ECDH_SHA2_STEM) - 1);
 	if (ret == -1)
 		fatal("%s: unsupported curve negotiated \"%s\"", __func__,
 		    kexname);
 	return ret;
 }
 
+const EVP_MD *
+kex_ecdh_name_to_evpmd(const char *kexname)
+{
+	int nid = kex_ecdh_name_to_nid(kexname);
+
+	return key_ec_nid_to_evpmd(nid);
+}
+
 void
 kex_ecdh_hash(
     const EVP_MD *evp_md,
diff --git a/usr.bin/ssh/key.c b/usr.bin/ssh/key.c
index 46cca3ef3c4..ba2709dfb4c 100644
--- a/usr.bin/ssh/key.c
+++ b/usr.bin/ssh/key.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: key.c,v 1.92 2010/08/31 11:54:45 djm Exp $ */
+/* $OpenBSD: key.c,v 1.93 2010/09/09 10:45:45 djm Exp $ */
 /*
  * read_bignum():
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -974,17 +974,7 @@ key_size(const Key *k)
 		return BN_num_bits(k->dsa->p);
 	case KEY_ECDSA:
 	case KEY_ECDSA_CERT:
-		switch (k->ecdsa_nid) {
-		case NID_X9_62_prime256v1:
-			return 256;
-		case NID_secp384r1:
-			return 384;
-		case NID_secp521r1:
-			return 521;
-		default:
-			break;
-		}
-		break;
+		return key_curve_nid_to_bits(k->ecdsa_nid);
 	}
 	return 0;
 }
@@ -1957,6 +1947,7 @@ key_cert_is_legacy(Key *k)
 	}
 }
 
+/* XXX: these are really begging for a table-driven approach */
 int
 key_curve_name_to_nid(const char *name)
 {
@@ -1971,6 +1962,22 @@ key_curve_name_to_nid(const char *name)
 	return -1;
 }
 
+u_int
+key_curve_nid_to_bits(int nid)
+{
+	switch (nid) {
+	case NID_X9_62_prime256v1:
+		return 256;
+	case NID_secp384r1:
+		return 384;
+	case NID_secp521r1:
+		return 521;
+	default:
+		error("%s: unsupported EC curve nid %d", __func__, nid);
+		return 0;
+	}
+}
+
 const char *
 key_curve_nid_to_name(int nid)
 {
@@ -1985,6 +1992,22 @@ key_curve_nid_to_name(int nid)
 	return NULL;
 }
 
+const EVP_MD *
+key_ec_nid_to_evpmd(int nid)
+{
+	int kbits = key_curve_nid_to_bits(nid);
+
+	if (kbits == 0)
+		fatal("%s: invalid nid %d", __func__, nid);
+	/* RFC5656 section 6.2.1 */
+	if (kbits <= 256)
+		return EVP_sha256();
+	else if (kbits <= 384)
+		return EVP_sha384();
+	else
+		return EVP_sha512();
+}
+
 int
 key_ec_validate_public(const EC_GROUP *group, const EC_POINT *public)
 {
diff --git a/usr.bin/ssh/key.h b/usr.bin/ssh/key.h
index 2eb1243646f..ba1a20c0754 100644
--- a/usr.bin/ssh/key.h
+++ b/usr.bin/ssh/key.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: key.h,v 1.31 2010/08/31 11:54:45 djm Exp $ */
+/* $OpenBSD: key.h,v 1.32 2010/09/09 10:45:45 djm Exp $ */
 
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
@@ -112,8 +112,10 @@ int	 key_cert_is_legacy(Key *);
 int		 key_ecdsa_nid_from_name(const char *);
 int		 key_curve_name_to_nid(const char *);
 const char *	 key_curve_nid_to_name(int);
+u_int		 key_curve_nid_to_bits(int);
 int		 key_ecdsa_bits_to_nid(int);
 int		 key_ecdsa_group_to_nid(const EC_GROUP *);
+const EVP_MD *	 key_ec_nid_to_evpmd(int nid);
 int		 key_ec_validate_public(const EC_GROUP *, const EC_POINT *);
 int		 key_ec_validate_private(const EC_KEY *);
 
diff --git a/usr.bin/ssh/monitor.c b/usr.bin/ssh/monitor.c
index 9c7755651f3..cb2ba89d6db 100644
--- a/usr.bin/ssh/monitor.c
+++ b/usr.bin/ssh/monitor.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: monitor.c,v 1.109 2010/08/31 11:54:45 djm Exp $ */
+/* $OpenBSD: monitor.c,v 1.110 2010/09/09 10:45:45 djm Exp $ */
 /*
  * Copyright 2002 Niels Provos <provos@citi.umich.edu>
  * Copyright 2002 Markus Friedl <markus@openbsd.org>
@@ -505,10 +505,10 @@ mm_answer_sign(int sock, Buffer *m)
 	p = buffer_get_string(m, &datlen);
 
 	/*
-	 * Supported KEX types will only return SHA1 (20 byte) or
-	 * SHA256 (32 byte) hashes
+	 * Supported KEX types use SHA1 (20 bytes), SHA256 (32 bytes),
+	 * SHA384 (48 bytes) and SHA512 (64 bytes).
 	 */
-	if (datlen != 20 && datlen != 32)
+	if (datlen != 20 && datlen != 32 && datlen != 48 && datlen != 64)
 		fatal("%s: data length incorrect: %u", __func__, datlen);
 
 	/* save session id, it will be passed on the first call */
diff --git a/usr.bin/ssh/ssh-ecdsa.c b/usr.bin/ssh/ssh-ecdsa.c
index 969fe5d6dca..74eba9b9d4e 100644
--- a/usr.bin/ssh/ssh-ecdsa.c
+++ b/usr.bin/ssh/ssh-ecdsa.c
@@ -44,7 +44,7 @@ ssh_ecdsa_sign(const Key *key, u_char **sigp, u_int *lenp,
     const u_char *data, u_int datalen)
 {
 	ECDSA_SIG *sig;
-	const EVP_MD *evp_md = EVP_sha256();
+	const EVP_MD *evp_md;
 	EVP_MD_CTX md;
 	u_char digest[EVP_MAX_MD_SIZE];
 	u_int len, dlen;
@@ -55,6 +55,7 @@ ssh_ecdsa_sign(const Key *key, u_char **sigp, u_int *lenp,
 		error("%s: no ECDSA key", __func__);
 		return -1;
 	}
+	evp_md = key_ec_nid_to_evpmd(key->ecdsa_nid);
 	EVP_DigestInit(&md, evp_md);
 	EVP_DigestUpdate(&md, data, datalen);
 	EVP_DigestFinal(&md, digest, &dlen);
@@ -92,7 +93,7 @@ ssh_ecdsa_verify(const Key *key, const u_char *signature, u_int signaturelen,
     const u_char *data, u_int datalen)
 {
 	ECDSA_SIG *sig;
-	const EVP_MD *evp_md = EVP_sha256();
+	const EVP_MD *evp_md;
 	EVP_MD_CTX md;
 	u_char digest[EVP_MAX_MD_SIZE], *sigblob;
 	u_int len, dlen;
@@ -105,6 +106,7 @@ ssh_ecdsa_verify(const Key *key, const u_char *signature, u_int signaturelen,
 		error("%s: no ECDSA key", __func__);
 		return -1;
 	}
+	evp_md = key_ec_nid_to_evpmd(key->ecdsa_nid);
 
 	/* fetch signature */
 	buffer_init(&b);