upstream: pass values used in KEX hash computation as sshbuf

rather than pointer+len

suggested by me; implemented by markus@ ok me

OpenBSD-Commit-ID: 994f33c464f4a9e0f1d21909fa3e379f5a0910f0

9 files changed, 98 insertions, 89 deletions

diff --git a/kex.h b/kex.h
index e3be3040..6798e33f 100644
--- a/kex.h
+++ b/kex.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: kex.h,v 1.103 2019/01/21 10:33:49 djm Exp $ */
+/* $OpenBSD: kex.h,v 1.104 2019/01/21 10:35:09 djm Exp $ */
 
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
@@ -211,24 +211,24 @@ int	 kex_kem_client(struct ssh *);
 int	 kex_kem_server(struct ssh *);
 
 int	 kex_dh_keypair(struct kex *);
-int	 kex_dh_enc(struct kex *, const u_char *, size_t, struct sshbuf **,
+int	 kex_dh_enc(struct kex *, const struct sshbuf *, struct sshbuf **,
     struct sshbuf **);
-int	 kex_dh_dec(struct kex *, const u_char *, size_t, struct sshbuf **);
+int	 kex_dh_dec(struct kex *, const struct sshbuf *, struct sshbuf **);
 
 int	 kex_ecdh_keypair(struct kex *);
-int	 kex_ecdh_enc(struct kex *, const u_char *, size_t, struct sshbuf **,
+int	 kex_ecdh_enc(struct kex *, const struct sshbuf *, struct sshbuf **,
     struct sshbuf **);
-int	 kex_ecdh_dec(struct kex *, const u_char *, size_t, struct sshbuf **);
+int	 kex_ecdh_dec(struct kex *, const struct sshbuf *, struct sshbuf **);
 
 int	 kex_c25519_keypair(struct kex *);
-int	 kex_c25519_enc(struct kex *, const u_char *, size_t, struct sshbuf **,
+int	 kex_c25519_enc(struct kex *, const struct sshbuf *, struct sshbuf **,
     struct sshbuf **);
-int	 kex_c25519_dec(struct kex *, const u_char *, size_t, struct sshbuf **);
+int	 kex_c25519_dec(struct kex *, const struct sshbuf *, struct sshbuf **);
 
 int	 kex_kem_sntrup4591761x25519_keypair(struct kex *);
-int	 kex_kem_sntrup4591761x25519_enc(struct kex *, const u_char *, size_t,
+int	 kex_kem_sntrup4591761x25519_enc(struct kex *, const struct sshbuf *,
     struct sshbuf **, struct sshbuf **);
-int	 kex_kem_sntrup4591761x25519_dec(struct kex *, const u_char *, size_t,
+int	 kex_kem_sntrup4591761x25519_dec(struct kex *, const struct sshbuf *,
     struct sshbuf **);
 
 int	 kex_dh_keygen(struct kex *);
@@ -243,8 +243,8 @@ int	 kexgex_hash(int, const struct sshbuf *, const struct sshbuf *,
 
 int	 kex_c25519_hash(int, const struct sshbuf *, const struct sshbuf *,
     const u_char *, size_t, const u_char *, size_t,
-    const u_char *, size_t, const u_char *, size_t, const u_char *, size_t,
-    const u_char *, size_t, u_char *, size_t *);
+    const u_char *, size_t, const struct sshbuf *, const struct sshbuf *,
+    const struct sshbuf *, u_char *, size_t *);
 
 void	kexc25519_keygen(u_char key[CURVE25519_SIZE], u_char pub[CURVE25519_SIZE])
 	__attribute__((__bounded__(__minbytes__, 1, CURVE25519_SIZE)))
diff --git a/kexc25519.c b/kexc25519.c
index a06c6e44..ec5bb574 100644
--- a/kexc25519.c
+++ b/kexc25519.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kexc25519.c,v 1.14 2019/01/21 10:24:09 djm Exp $ */
+/* $OpenBSD: kexc25519.c,v 1.15 2019/01/21 10:35:09 djm Exp $ */
 /*
  * Copyright (c) 2019 Markus Friedl.  All rights reserved.
  * Copyright (c) 2010 Damien Miller.  All rights reserved.
@@ -96,9 +96,9 @@ kex_c25519_hash(
     const u_char *ckexinit, size_t ckexinitlen,
     const u_char *skexinit, size_t skexinitlen,
     const u_char *serverhostkeyblob, size_t sbloblen,
-    const u_char *client_pub, size_t client_pub_len,
-    const u_char *server_pub, size_t server_pub_len,
-    const u_char *shared_secret, size_t secretlen,
+    const struct sshbuf *client_pub,
+    const struct sshbuf *server_pub,
+    const struct sshbuf *shared_secret,
     u_char *hash, size_t *hashlen)
 {
 	struct sshbuf *b;
@@ -118,9 +118,9 @@ kex_c25519_hash(
 	    (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) != 0 ||
 	    (r = sshbuf_put(b, skexinit, skexinitlen)) != 0 ||
 	    (r = sshbuf_put_string(b, serverhostkeyblob, sbloblen)) != 0 ||
-	    (r = sshbuf_put_string(b, client_pub, client_pub_len)) != 0 ||
-	    (r = sshbuf_put_string(b, server_pub, server_pub_len)) != 0 ||
-	    (r = sshbuf_put(b, shared_secret, secretlen)) != 0) {
+	    (r = sshbuf_put_stringb(b, client_pub)) != 0 ||
+	    (r = sshbuf_put_stringb(b, server_pub)) != 0 ||
+	    (r = sshbuf_putb(b, shared_secret)) != 0) {
 		sshbuf_free(b);
 		return r;
 	}
@@ -162,11 +162,12 @@ kex_c25519_keypair(struct kex *kex)
 }
 
 int
-kex_c25519_enc(struct kex *kex, const u_char *pkblob,
-   size_t pklen, struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
+kex_c25519_enc(struct kex *kex, const struct sshbuf *client_blob,
+   struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
 {
 	struct sshbuf *server_blob = NULL;
 	struct sshbuf *buf = NULL;
+	const u_char *client_pub;
 	u_char *server_pub;
 	u_char server_key[CURVE25519_SIZE];
 	int r;
@@ -174,12 +175,13 @@ kex_c25519_enc(struct kex *kex, const u_char *pkblob,
 	*server_blobp = NULL;
 	*shared_secretp = NULL;
 
-	if (pklen != CURVE25519_SIZE) {
+	if (sshbuf_len(client_blob) != CURVE25519_SIZE) {
 		r = SSH_ERR_SIGNATURE_INVALID;
 		goto out;
 	}
+	client_pub = sshbuf_ptr(client_blob);
 #ifdef DEBUG_KEXECDH
-	dump_digest("client public key 25519:", pkblob, CURVE25519_SIZE);
+	dump_digest("client public key 25519:", client_pub, CURVE25519_SIZE);
 #endif
 	/* allocate space for encrypted KEM key and ECDH pub key */
 	if ((server_blob = sshbuf_new()) == NULL) {
@@ -194,7 +196,7 @@ kex_c25519_enc(struct kex *kex, const u_char *pkblob,
 		r = SSH_ERR_ALLOC_FAIL;
 		goto out;
 	}
-	if ((r = kexc25519_shared_key_ext(server_key, pkblob, buf, 0)) < 0)
+	if ((r = kexc25519_shared_key_ext(server_key, client_pub, buf, 0)) < 0)
 		goto out;
 #ifdef DEBUG_KEXECDH
 	dump_digest("server public key 25519:", server_pub, CURVE25519_SIZE);
@@ -212,27 +214,29 @@ kex_c25519_enc(struct kex *kex, const u_char *pkblob,
 }
 
 int
-kex_c25519_dec(struct kex *kex, const u_char *pkblob,
-    size_t pklen, struct sshbuf **shared_secretp)
+kex_c25519_dec(struct kex *kex, const struct sshbuf *server_blob,
+    struct sshbuf **shared_secretp)
 {
 	struct sshbuf *buf = NULL;
+	const u_char *server_pub;
 	int r;
 
 	*shared_secretp = NULL;
 
-	if (pklen != CURVE25519_SIZE) {
+	if (sshbuf_len(server_blob) != CURVE25519_SIZE) {
 		r = SSH_ERR_SIGNATURE_INVALID;
 		goto out;
 	}
+	server_pub = sshbuf_ptr(server_blob);
 #ifdef DEBUG_KEXECDH
-	dump_digest("server public key c25519:", pkblob, CURVE25519_SIZE);
+	dump_digest("server public key c25519:", server_pub, CURVE25519_SIZE);
 #endif
 	/* shared secret */
 	if ((buf = sshbuf_new()) == NULL) {
 		r = SSH_ERR_ALLOC_FAIL;
 		goto out;
 	}
-	if ((r = kexc25519_shared_key_ext(kex->c25519_client_key, pkblob,
+	if ((r = kexc25519_shared_key_ext(kex->c25519_client_key, server_pub,
 	    buf, 0)) < 0)
 		goto out;
 #ifdef DEBUG_KEXECDH
diff --git a/kexdh.c b/kexdh.c
index 98597ead..94377462 100644
--- a/kexdh.c
+++ b/kexdh.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kexdh.c,v 1.30 2019/01/21 10:28:01 djm Exp $ */
+/* $OpenBSD: kexdh.c,v 1.31 2019/01/21 10:35:09 djm Exp $ */
 /*
  * Copyright (c) 2019 Markus Friedl.  All rights reserved.
  *
@@ -136,7 +136,7 @@ kex_dh_keypair(struct kex *kex)
 }
 
 int
-kex_dh_enc(struct kex *kex, const u_char *pkblob, size_t pklen,
+kex_dh_enc(struct kex *kex, const struct sshbuf *client_blob,
     struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
 {
 	const BIGNUM *pub_key;
@@ -156,7 +156,7 @@ kex_dh_enc(struct kex *kex, const u_char *pkblob, size_t pklen,
 	if ((r = sshbuf_put_bignum2(server_blob, pub_key)) != 0 ||
 	    (r = sshbuf_get_u32(server_blob, NULL)) != 0)
 		goto out;
-	if ((r = kex_dh_dec(kex, pkblob, pklen, shared_secretp)) != 0)
+	if ((r = kex_dh_dec(kex, client_blob, shared_secretp)) != 0)
 		goto out;
 	*server_blobp = server_blob;
 	server_blob = NULL;
@@ -168,7 +168,7 @@ kex_dh_enc(struct kex *kex, const u_char *pkblob, size_t pklen,
 }
 
 int
-kex_dh_dec(struct kex *kex, const u_char *pkblob, size_t pklen,
+kex_dh_dec(struct kex *kex, const struct sshbuf *dh_blob,
     struct sshbuf **shared_secretp)
 {
 	struct sshbuf *buf = NULL;
@@ -181,13 +181,9 @@ kex_dh_dec(struct kex *kex, const u_char *pkblob, size_t pklen,
 		r = SSH_ERR_ALLOC_FAIL;
 		goto out;
 	}
-	if ((r = sshbuf_put_u32(buf, pklen)) != 0 ||
-	    (r = sshbuf_put(buf, pkblob, pklen)) != 0) {
+	if ((r = sshbuf_put_stringb(buf, dh_blob)) != 0 ||
+	    (r = sshbuf_get_bignum2(buf, &dh_pub)) != 0)
 		goto out;
-	}
-	if ((r = sshbuf_get_bignum2(buf, &dh_pub)) != 0) {
-		goto out;
-	}
 	sshbuf_reset(buf);
 	if ((r = kex_dh_compute_key(kex, dh_pub, buf)) != 0)
 		goto out;
diff --git a/kexecdh.c b/kexecdh.c
index 263f9fd8..ae901877 100644
--- a/kexecdh.c
+++ b/kexecdh.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kexecdh.c,v 1.8 2019/01/21 10:29:56 djm Exp $ */
+/* $OpenBSD: kexecdh.c,v 1.9 2019/01/21 10:35:09 djm Exp $ */
 /*
  * Copyright (c) 2010 Damien Miller.  All rights reserved.
  * Copyright (c) 2019 Markus Friedl.  All rights reserved.
@@ -43,7 +43,7 @@
 #include "ssherr.h"
 
 static int
-kex_ecdh_dec_key_group(struct kex *, const u_char *, size_t, EC_KEY *key,
+kex_ecdh_dec_key_group(struct kex *, const struct sshbuf *, EC_KEY *key,
     const EC_GROUP *, struct sshbuf **);
 
 int
@@ -89,7 +89,7 @@ kex_ecdh_keypair(struct kex *kex)
 }
 
 int
-kex_ecdh_enc(struct kex *kex, const u_char *pkblob, size_t pklen,
+kex_ecdh_enc(struct kex *kex, const struct sshbuf *client_blob,
     struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
 {
 	const EC_GROUP *group;
@@ -123,7 +123,7 @@ kex_ecdh_enc(struct kex *kex, const u_char *pkblob, size_t pklen,
 	if ((r = sshbuf_put_ec(server_blob, pub_key, group)) != 0 ||
 	    (r = sshbuf_get_u32(server_blob, NULL)) != 0)
 		goto out;
-	if ((r = kex_ecdh_dec_key_group(kex, pkblob, pklen, server_key, group,
+	if ((r = kex_ecdh_dec_key_group(kex, client_blob, server_key, group,
 	    shared_secretp)) != 0)
 		goto out;
 	*server_blobp = server_blob;
@@ -135,7 +135,7 @@ kex_ecdh_enc(struct kex *kex, const u_char *pkblob, size_t pklen,
 }
 
 static int
-kex_ecdh_dec_key_group(struct kex *kex, const u_char *pkblob, size_t pklen,
+kex_ecdh_dec_key_group(struct kex *kex, const struct sshbuf *ec_blob,
     EC_KEY *key, const EC_GROUP *group, struct sshbuf **shared_secretp)
 {
 	struct sshbuf *buf = NULL;
@@ -151,10 +151,8 @@ kex_ecdh_dec_key_group(struct kex *kex, const u_char *pkblob, size_t pklen,
 		r = SSH_ERR_ALLOC_FAIL;
 		goto out;
 	}
-	if ((r = sshbuf_put_u32(buf, pklen)) != 0 ||
-	    (r = sshbuf_put(buf, pkblob, pklen)) != 0) {
+	if ((r = sshbuf_put_stringb(buf, ec_blob)) != 0)
 		goto out;
-	}
 	if ((dh_pub = EC_POINT_new(group)) == NULL) {
 		r = SSH_ERR_ALLOC_FAIL;
 		goto out;
@@ -199,12 +197,12 @@ kex_ecdh_dec_key_group(struct kex *kex, const u_char *pkblob, size_t pklen,
 }
 
 int
-kex_ecdh_dec(struct kex *kex, const u_char *pkblob, size_t pklen,
+kex_ecdh_dec(struct kex *kex, const struct sshbuf *server_blob,
     struct sshbuf **shared_secretp)
 {
 	int r;
 
-	r = kex_ecdh_dec_key_group(kex, pkblob, pklen, kex->ec_client_key,
+	r = kex_ecdh_dec_key_group(kex, server_blob, kex->ec_client_key,
 	    kex->ec_group, shared_secretp);
 	EC_KEY_free(kex->ec_client_key);
 	kex->ec_client_key = NULL;
diff --git a/kexkemc.c b/kexkemc.c
index 55055de2..942be574 100644
--- a/kexkemc.c
+++ b/kexkemc.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kexkemc.c,v 1.4 2019/01/21 10:29:56 djm Exp $ */
+/* $OpenBSD: kexkemc.c,v 1.5 2019/01/21 10:35:09 djm Exp $ */
 /*
  * Copyright (c) 2019 Markus Friedl.  All rights reserved.
  *
@@ -85,10 +85,10 @@ input_kex_kem_reply(int type, u_int32_t seq, struct ssh *ssh)
 	struct kex *kex = ssh->kex;
 	struct sshkey *server_host_key = NULL;
 	struct sshbuf *shared_secret = NULL;
-	u_char *server_pubkey = NULL;
+	struct sshbuf *server_blob = NULL;
 	u_char *server_host_key_blob = NULL, *signature = NULL;
 	u_char hash[SSH_DIGEST_MAX_LENGTH];
-	size_t slen, pklen, sbloblen, hashlen;
+	size_t slen, sbloblen, hashlen;
 	int r;
 
 	/* hostkey */
@@ -102,7 +102,7 @@ input_kex_kem_reply(int type, u_int32_t seq, struct ssh *ssh)
 
 	/* Q_S, server public key */
 	/* signed H */
-	if ((r = sshpkt_get_string(ssh, &server_pubkey, &pklen)) != 0 ||
+	if ((r = sshpkt_getb_froms(ssh, &server_blob)) != 0 ||
 	    (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 ||
 	    (r = sshpkt_get_end(ssh)) != 0)
 		goto out;
@@ -114,16 +114,16 @@ input_kex_kem_reply(int type, u_int32_t seq, struct ssh *ssh)
 	case KEX_DH_GRP14_SHA256:
 	case KEX_DH_GRP16_SHA512:
 	case KEX_DH_GRP18_SHA512:
-		r = kex_dh_dec(kex, server_pubkey, pklen, &shared_secret);
+		r = kex_dh_dec(kex, server_blob, &shared_secret);
 		break;
 	case KEX_ECDH_SHA2:
-		r = kex_ecdh_dec(kex, server_pubkey, pklen, &shared_secret);
+		r = kex_ecdh_dec(kex, server_blob, &shared_secret);
 		break;
 	case KEX_C25519_SHA256:
-		r = kex_c25519_dec(kex, server_pubkey, pklen, &shared_secret);
+		r = kex_c25519_dec(kex, server_blob, &shared_secret);
 		break;
 	case KEX_KEM_SNTRUP4591761X25519_SHA512:
-		r = kex_kem_sntrup4591761x25519_dec(kex, server_pubkey, pklen,
+		r = kex_kem_sntrup4591761x25519_dec(kex, server_blob,
 		    &shared_secret);
 		break;
 	default:
@@ -142,9 +142,9 @@ input_kex_kem_reply(int type, u_int32_t seq, struct ssh *ssh)
 	    sshbuf_ptr(kex->my), sshbuf_len(kex->my),
 	    sshbuf_ptr(kex->peer), sshbuf_len(kex->peer),
 	    server_host_key_blob, sbloblen,
-	    sshbuf_ptr(kex->kem_client_pub), sshbuf_len(kex->kem_client_pub),
-	    server_pubkey, pklen,
-	    sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
+	    kex->kem_client_pub,
+	    server_blob,
+	    shared_secret,
 	    hash, &hashlen)) != 0)
 		goto out;
 
@@ -160,9 +160,9 @@ out:
 	explicit_bzero(kex->sntrup4591761_client_key,
 	    sizeof(kex->sntrup4591761_client_key));
 	free(server_host_key_blob);
-	free(server_pubkey);
 	free(signature);
 	sshkey_free(server_host_key);
+	sshbuf_free(server_blob);
 	sshbuf_free(shared_secret);
 	sshbuf_free(kex->kem_client_pub);
 	kex->kem_client_pub = NULL;
diff --git a/kexkems.c b/kexkems.c
index 10ef1219..3ba8f0df 100644
--- a/kexkems.c
+++ b/kexkems.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kexkems.c,v 1.4 2019/01/21 10:29:56 djm Exp $ */
+/* $OpenBSD: kexkems.c,v 1.5 2019/01/21 10:35:09 djm Exp $ */
 /*
  * Copyright (c) 2019 Markus Friedl.  All rights reserved.
  *
@@ -53,17 +53,17 @@ input_kex_kem_init(int type, u_int32_t seq, struct ssh *ssh)
 	struct sshkey *server_host_private, *server_host_public;
 	struct sshbuf *shared_secret = NULL;
 	struct sshbuf *server_pubkey = NULL;
+	struct sshbuf *client_pubkey = NULL;
 	u_char *server_host_key_blob = NULL, *signature = NULL;
-	u_char *client_pubkey = NULL;
 	u_char hash[SSH_DIGEST_MAX_LENGTH];
-	size_t slen, pklen, sbloblen, hashlen;
+	size_t slen, sbloblen, hashlen;
 	int r;
 
 	if ((r = kex_load_hostkey(ssh, &server_host_private,
 	    &server_host_public)) != 0)
 		goto out;
 
-	if ((r = sshpkt_get_string(ssh, &client_pubkey, &pklen)) != 0 ||
+	if ((r = sshpkt_getb_froms(ssh, &client_pubkey)) != 0 ||
 	    (r = sshpkt_get_end(ssh)) != 0)
 		goto out;
 
@@ -74,19 +74,19 @@ input_kex_kem_init(int type, u_int32_t seq, struct ssh *ssh)
 	case KEX_DH_GRP14_SHA256:
 	case KEX_DH_GRP16_SHA512:
 	case KEX_DH_GRP18_SHA512:
-		r = kex_dh_enc(kex, client_pubkey, pklen, &server_pubkey,
+		r = kex_dh_enc(kex, client_pubkey, &server_pubkey,
 		    &shared_secret);
 		break;
 	case KEX_ECDH_SHA2:
-		r = kex_ecdh_enc(kex, client_pubkey, pklen, &server_pubkey,
+		r = kex_ecdh_enc(kex, client_pubkey, &server_pubkey,
 		    &shared_secret);
 		break;
 	case KEX_C25519_SHA256:
-		r = kex_c25519_enc(kex, client_pubkey, pklen, &server_pubkey,
+		r = kex_c25519_enc(kex, client_pubkey, &server_pubkey,
 		    &shared_secret);
 		break;
 	case KEX_KEM_SNTRUP4591761X25519_SHA512:
-		r = kex_kem_sntrup4591761x25519_enc(kex, client_pubkey, pklen,
+		r = kex_kem_sntrup4591761x25519_enc(kex, client_pubkey,
 		    &server_pubkey, &shared_secret);
 		break;
 	default:
@@ -108,9 +108,9 @@ input_kex_kem_init(int type, u_int32_t seq, struct ssh *ssh)
 	    sshbuf_ptr(kex->peer), sshbuf_len(kex->peer),
 	    sshbuf_ptr(kex->my), sshbuf_len(kex->my),
 	    server_host_key_blob, sbloblen,
-	    client_pubkey, pklen,
-	    sshbuf_ptr(server_pubkey), sshbuf_len(server_pubkey),
-	    sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
+	    client_pubkey,
+	    server_pubkey,
+	    shared_secret,
 	    hash, &hashlen)) != 0)
 		goto out;
 
@@ -133,8 +133,8 @@ out:
 	explicit_bzero(hash, sizeof(hash));
 	free(server_host_key_blob);
 	free(signature);
-	free(client_pubkey);
 	sshbuf_free(shared_secret);
+	sshbuf_free(client_pubkey);
 	sshbuf_free(server_pubkey);
 	return r;
 }
diff --git a/kexsntrup4591761x25519.c b/kexsntrup4591761x25519.c
index ffe05f42..d845f3d4 100644
--- a/kexsntrup4591761x25519.c
+++ b/kexsntrup4591761x25519.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kexsntrup4591761x25519.c,v 1.1 2019/01/21 10:20:12 djm Exp $ */
+/* $OpenBSD: kexsntrup4591761x25519.c,v 1.2 2019/01/21 10:35:09 djm Exp $ */
 /*
  * Copyright (c) 2019 Markus Friedl.  All rights reserved.
  *
@@ -66,11 +66,13 @@ kex_kem_sntrup4591761x25519_keypair(struct kex *kex)
 }
 
 int
-kex_kem_sntrup4591761x25519_enc(struct kex *kex, const u_char *pkblob,
-   size_t pklen, struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
+kex_kem_sntrup4591761x25519_enc(struct kex *kex,
+   const struct sshbuf *client_blob, struct sshbuf **server_blobp,
+   struct sshbuf **shared_secretp)
 {
 	struct sshbuf *server_blob = NULL;
 	struct sshbuf *buf = NULL;
+	const u_char *client_pub;
 	u_char *kem_key, *ciphertext, *server_pub;
 	u_char server_key[CURVE25519_SIZE];
 	u_char hash[SSH_DIGEST_MAX_LENGTH];
@@ -80,17 +82,19 @@ kex_kem_sntrup4591761x25519_enc(struct kex *kex, const u_char *pkblob,
 	*server_blobp = NULL;
 	*shared_secretp = NULL;
 
-	/* pkblob contains both KEM and ECDH client pubkeys */
+	/* client_blob contains both KEM and ECDH client pubkeys */
 	need = crypto_kem_sntrup4591761_PUBLICKEYBYTES + CURVE25519_SIZE;
-	if (pklen != need) {
+	if (sshbuf_len(client_blob) != need) {
 		r = SSH_ERR_SIGNATURE_INVALID;
 		goto out;
 	}
+	client_pub = sshbuf_ptr(client_blob);
 #ifdef DEBUG_KEXECDH
-	dump_digest("client public key sntrup4591761:", pkblob,
+	dump_digest("client public key sntrup4591761:", client_pub,
 	    crypto_kem_sntrup4591761_PUBLICKEYBYTES);
 	dump_digest("client public key 25519:",
-	    pkblob + crypto_kem_sntrup4591761_PUBLICKEYBYTES, CURVE25519_SIZE);
+	    client_pub + crypto_kem_sntrup4591761_PUBLICKEYBYTES,
+	    CURVE25519_SIZE);
 #endif
 	/* allocate buffer for concatenation of KEM key and ECDH shared key */
 	/* the buffer will be hashed and the result is the shared secret */
@@ -110,13 +114,13 @@ kex_kem_sntrup4591761x25519_enc(struct kex *kex, const u_char *pkblob,
 	if ((r = sshbuf_reserve(server_blob, need, &ciphertext)) != 0)
 		goto out;
 	/* generate and encrypt KEM key with client key */
-	crypto_kem_sntrup4591761_enc(ciphertext, kem_key, pkblob);
+	crypto_kem_sntrup4591761_enc(ciphertext, kem_key, client_pub);
 	/* generate ECDH key pair, store server pubkey after ciphertext */
 	server_pub = ciphertext + crypto_kem_sntrup4591761_CIPHERTEXTBYTES;
 	kexc25519_keygen(server_key, server_pub);
 	/* append ECDH shared key */
-	if ((r = kexc25519_shared_key_ext(server_key,
-	    pkblob + crypto_kem_sntrup4591761_PUBLICKEYBYTES, buf, 1)) < 0)
+	client_pub += crypto_kem_sntrup4591761_PUBLICKEYBYTES;
+	if ((r = kexc25519_shared_key_ext(server_key, client_pub, buf, 1)) < 0)
 		goto out;
 	if ((r = ssh_digest_buffer(kex->hash_alg, buf, hash, sizeof(hash))) != 0)
 		goto out;
@@ -149,8 +153,8 @@ kex_kem_sntrup4591761x25519_enc(struct kex *kex, const u_char *pkblob,
 }
 
 int
-kex_kem_sntrup4591761x25519_dec(struct kex *kex, const u_char *pkblob,
-    size_t pklen, struct sshbuf **shared_secretp)
+kex_kem_sntrup4591761x25519_dec(struct kex *kex,
+    const struct sshbuf *server_blob, struct sshbuf **shared_secretp)
 {
 	struct sshbuf *buf = NULL;
 	u_char *kem_key = NULL;
@@ -162,12 +166,12 @@ kex_kem_sntrup4591761x25519_dec(struct kex *kex, const u_char *pkblob,
 	*shared_secretp = NULL;
 
 	need = crypto_kem_sntrup4591761_CIPHERTEXTBYTES + CURVE25519_SIZE;
-	if (pklen != need) {
+	if (sshbuf_len(server_blob) != need) {
 		r = SSH_ERR_SIGNATURE_INVALID;
 		goto out;
 	}
-	ciphertext = pkblob;
-	server_pub = pkblob + crypto_kem_sntrup4591761_CIPHERTEXTBYTES;
+	ciphertext = sshbuf_ptr(server_blob);
+	server_pub = ciphertext + crypto_kem_sntrup4591761_CIPHERTEXTBYTES;
 #ifdef DEBUG_KEXECDH
 	dump_digest("server cipher text:", ciphertext,
 	    crypto_kem_sntrup4591761_CIPHERTEXTBYTES);
diff --git a/packet.c b/packet.c
index a162791b..ec03301b 100644
--- a/packet.c
+++ b/packet.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: packet.c,v 1.281 2019/01/21 09:54:11 djm Exp $ */
+/* $OpenBSD: packet.c,v 1.282 2019/01/21 10:35:09 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -2483,6 +2483,12 @@ sshpkt_put_stringb(struct ssh *ssh, const struct sshbuf *v)
 	return sshbuf_put_stringb(ssh->state->outgoing_packet, v);
 }
 
+int
+sshpkt_getb_froms(struct ssh *ssh, struct sshbuf **valp)
+{
+	return sshbuf_froms(ssh->state->incoming_packet, valp);
+}
+
 #ifdef WITH_OPENSSL
 #ifdef OPENSSL_HAS_ECC
 int
diff --git a/packet.h b/packet.h
index 98338f1f..0dfa36da 100644
--- a/packet.h
+++ b/packet.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: packet.h,v 1.89 2019/01/21 09:54:11 djm Exp $ */
+/* $OpenBSD: packet.h,v 1.90 2019/01/21 10:35:09 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -199,6 +199,7 @@ int	sshpkt_get_string(struct ssh *ssh, u_char **valp, size_t *lenp);
 int	sshpkt_get_string_direct(struct ssh *ssh, const u_char **valp, size_t *lenp);
 int	sshpkt_peek_string_direct(struct ssh *ssh, const u_char **valp, size_t *lenp);
 int	sshpkt_get_cstring(struct ssh *ssh, char **valp, size_t *lenp);
+int	sshpkt_getb_froms(struct ssh *ssh, struct sshbuf **valp);
 int	sshpkt_get_ec(struct ssh *ssh, EC_POINT *v, const EC_GROUP *g);
 int	sshpkt_get_bignum2(struct ssh *ssh, BIGNUM **valp);
 int	sshpkt_get_end(struct ssh *ssh);