- djm@cvs.openbsd.org 2014/01/12 08:13:13

[bufaux.c buffer.h kex.c kex.h kexc25519.c kexc25519c.c kexc25519s.c]
     [kexdhc.c kexdhs.c kexecdhc.c kexecdhs.c kexgexc.c kexgexs.c]
     avoid use of OpenSSL BIGNUM type and functions for KEX with
     Curve25519 by adding a buffer_put_bignum2_from_string() that stores
     a string using the bignum encoding rules. Will make it easier to
     build a reduced-feature OpenSSH without OpenSSL in the future;
     ok markus@
This commit is contained in:
Damien Miller 2014-01-12 19:21:22 +11:00
parent af5d4481f4
commit 91b580e4be
14 changed files with 147 additions and 48 deletions

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@ -3,6 +3,14 @@
- djm@cvs.openbsd.org 2014/01/10 05:59:19
[sshd_config]
the /etc/ssh/ssh_host_ed25519_key is loaded by default too
- djm@cvs.openbsd.org 2014/01/12 08:13:13
[bufaux.c buffer.h kex.c kex.h kexc25519.c kexc25519c.c kexc25519s.c]
[kexdhc.c kexdhs.c kexecdhc.c kexecdhs.c kexgexc.c kexgexs.c]
avoid use of OpenSSL BIGNUM type and functions for KEX with
Curve25519 by adding a buffer_put_bignum2_from_string() that stores
a string using the bignum encoding rules. Will make it easier to
build a reduced-feature OpenSSH without OpenSSL in the future;
ok markus@
20140110
- (djm) OpenBSD CVS Sync

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@ -1,4 +1,4 @@
/* $OpenBSD: bufaux.c,v 1.53 2013/11/08 11:15:19 dtucker Exp $ */
/* $OpenBSD: bufaux.c,v 1.54 2014/01/12 08:13:13 djm Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@ -315,3 +315,76 @@ buffer_put_char(Buffer *buffer, int value)
buffer_append(buffer, &ch, 1);
}
/* Pseudo bignum functions */
void *
buffer_get_bignum2_as_string_ret(Buffer *buffer, u_int *length_ptr)
{
u_int len;
u_char *bin, *p, *ret;
if ((p = bin = buffer_get_string_ret(buffer, &len)) == NULL) {
error("%s: invalid bignum", __func__);
return NULL;
}
if (len > 0 && (bin[0] & 0x80)) {
error("%s: negative numbers not supported", __func__);
free(bin);
return NULL;
}
if (len > 8 * 1024) {
error("%s: cannot handle BN of size %d", __func__, len);
free(bin);
return NULL;
}
/* Skip zero prefix on numbers with the MSB set */
if (len > 1 && bin[0] == 0x00 && (bin[1] & 0x80) != 0) {
p++;
len--;
}
ret = xmalloc(len);
memcpy(ret, p, len);
memset(p, '\0', len);
free(bin);
return ret;
}
void *
buffer_get_bignum2_as_string(Buffer *buffer, u_int *l)
{
void *ret = buffer_get_bignum2_as_string_ret(buffer, l);
if (ret == NULL)
fatal("%s: buffer error", __func__);
return ret;
}
/*
* Stores a string using the bignum encoding rules (\0 pad if MSB set).
*/
void
buffer_put_bignum2_from_string(Buffer *buffer, const u_char *s, u_int l)
{
u_char *buf, *p;
int pad = 0;
if (l > 8 * 1024)
fatal("%s: length %u too long", __func__, l);
p = buf = xmalloc(l + 1);
/*
* If most significant bit is set then prepend a zero byte to
* avoid interpretation as a negative number.
*/
if (l > 0 && (s[0] & 0x80) != 0) {
*p++ = '\0';
pad = 1;
}
memcpy(p, s, l);
buffer_put_string(buffer, buf, l + pad);
memset(buf, '\0', l + pad);
free(buf);
}

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@ -1,4 +1,4 @@
/* $OpenBSD: buffer.h,v 1.22 2013/07/12 00:19:58 djm Exp $ */
/* $OpenBSD: buffer.h,v 1.23 2014/01/12 08:13:13 djm Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
@ -86,6 +86,10 @@ char *buffer_get_cstring_ret(Buffer *, u_int *);
void *buffer_get_string_ptr_ret(Buffer *, u_int *);
int buffer_get_char_ret(u_char *, Buffer *);
void *buffer_get_bignum2_as_string_ret(Buffer *, u_int *);
void *buffer_get_bignum2_as_string(Buffer *, u_int *);
void buffer_put_bignum2_from_string(Buffer *, const u_char *, u_int);
#ifdef OPENSSL_HAS_ECC
#include <openssl/ec.h>

23
kex.c
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@ -1,4 +1,4 @@
/* $OpenBSD: kex.c,v 1.94 2014/01/09 23:20:00 djm Exp $ */
/* $OpenBSD: kex.c,v 1.95 2014/01/12 08:13:13 djm Exp $ */
/*
* Copyright (c) 2000, 2001 Markus Friedl. All rights reserved.
*
@ -534,7 +534,7 @@ kex_choose_conf(Kex *kex)
static u_char *
derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
BIGNUM *shared_secret)
const u_char *shared_secret, u_int slen)
{
Buffer b;
struct ssh_digest_ctx *hashctx;
@ -548,7 +548,7 @@ derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
digest = xmalloc(roundup(need, mdsz));
buffer_init(&b);
buffer_put_bignum2(&b, shared_secret);
buffer_append(&b, shared_secret, slen);
/* K1 = HASH(K || H || "A" || session_id) */
if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL)
@ -591,14 +591,15 @@ Newkeys *current_keys[MODE_MAX];
#define NKEYS 6
void
kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen,
const u_char *shared_secret, u_int slen)
{
u_char *keys[NKEYS];
u_int i, mode, ctos;
for (i = 0; i < NKEYS; i++) {
keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
shared_secret);
shared_secret, slen);
}
debug2("kex_derive_keys");
@ -613,6 +614,18 @@ kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
}
}
void
kex_derive_keys_bn(Kex *kex, u_char *hash, u_int hashlen, const BIGNUM *secret)
{
Buffer shared_secret;
buffer_init(&shared_secret);
buffer_put_bignum2(&shared_secret, secret);
kex_derive_keys(kex, hash, hashlen,
buffer_ptr(&shared_secret), buffer_len(&shared_secret));
buffer_free(&shared_secret);
}
Newkeys *
kex_get_newkeys(int mode)
{

11
kex.h
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@ -1,4 +1,4 @@
/* $OpenBSD: kex.h,v 1.59 2014/01/09 23:20:00 djm Exp $ */
/* $OpenBSD: kex.h,v 1.60 2014/01/12 08:13:13 djm Exp $ */
/*
* Copyright (c) 2000, 2001 Markus Friedl. All rights reserved.
@ -153,7 +153,8 @@ void kex_finish(Kex *);
void kex_send_kexinit(Kex *);
void kex_input_kexinit(int, u_int32_t, void *);
void kex_derive_keys(Kex *, u_char *, u_int, BIGNUM *);
void kex_derive_keys(Kex *, u_char *, u_int, const u_char *, u_int);
void kex_derive_keys_bn(Kex *, u_char *, u_int, const BIGNUM *);
Newkeys *kex_get_newkeys(int);
@ -182,14 +183,14 @@ kex_ecdh_hash(int, const EC_GROUP *, char *, char *, char *, int,
void
kex_c25519_hash(int, char *, char *, char *, int,
char *, int, u_char *, int, const u_char *, const u_char *,
const BIGNUM *, u_char **, u_int *);
const u_char *, u_int, u_char **, u_int *);
#define CURVE25519_SIZE 32
void kexc25519_keygen(u_char[CURVE25519_SIZE], u_char[CURVE25519_SIZE])
__attribute__((__bounded__(__minbytes__, 1, CURVE25519_SIZE)))
__attribute__((__bounded__(__minbytes__, 2, CURVE25519_SIZE)));
BIGNUM *kexc25519_shared_key(const u_char[CURVE25519_SIZE],
const u_char[CURVE25519_SIZE])
void kexc25519_shared_key(const u_char key[CURVE25519_SIZE],
const u_char pub[CURVE25519_SIZE], Buffer *out)
__attribute__((__bounded__(__minbytes__, 1, CURVE25519_SIZE)))
__attribute__((__bounded__(__minbytes__, 2, CURVE25519_SIZE)));

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@ -1,4 +1,4 @@
/* $OpenBSD: kexc25519.c,v 1.3 2014/01/09 23:20:00 djm Exp $ */
/* $OpenBSD: kexc25519.c,v 1.4 2014/01/12 08:13:13 djm Exp $ */
/*
* Copyright (c) 2001, 2013 Markus Friedl. All rights reserved.
* Copyright (c) 2010 Damien Miller. All rights reserved.
@ -58,23 +58,19 @@ kexc25519_keygen(u_char key[CURVE25519_SIZE], u_char pub[CURVE25519_SIZE])
crypto_scalarmult_curve25519(pub, key, basepoint);
}
BIGNUM *
void
kexc25519_shared_key(const u_char key[CURVE25519_SIZE],
const u_char pub[CURVE25519_SIZE])
const u_char pub[CURVE25519_SIZE], Buffer *out)
{
u_char shared_key[CURVE25519_SIZE];
BIGNUM *shared_secret;
crypto_scalarmult_curve25519(shared_key, key, pub);
#ifdef DEBUG_KEXECDH
dump_digest("shared secret", shared_key, CURVE25519_SIZE);
#endif
if ((shared_secret = BN_new()) == NULL)
fatal("%s: BN_new failed", __func__);
if (BN_bin2bn(shared_key, sizeof(shared_key), shared_secret) == NULL)
fatal("%s: BN_bin2bn failed", __func__);
buffer_clear(out);
buffer_put_bignum2_from_string(out, shared_key, CURVE25519_SIZE);
memset(shared_key, 0, CURVE25519_SIZE); /* XXX explicit_bzero() */
return (shared_secret);
}
void
@ -87,7 +83,7 @@ kex_c25519_hash(
u_char *serverhostkeyblob, int sbloblen,
const u_char client_dh_pub[CURVE25519_SIZE],
const u_char server_dh_pub[CURVE25519_SIZE],
const BIGNUM *shared_secret,
const u_char *shared_secret, u_int secretlen,
u_char **hash, u_int *hashlen)
{
Buffer b;
@ -108,7 +104,7 @@ kex_c25519_hash(
buffer_put_string(&b, serverhostkeyblob, sbloblen);
buffer_put_string(&b, client_dh_pub, CURVE25519_SIZE);
buffer_put_string(&b, server_dh_pub, CURVE25519_SIZE);
buffer_put_bignum2(&b, shared_secret);
buffer_append(&b, shared_secret, secretlen);
#ifdef DEBUG_KEX
buffer_dump(&b);

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@ -1,4 +1,4 @@
/* $OpenBSD: kexc25519c.c,v 1.3 2014/01/09 23:20:00 djm Exp $ */
/* $OpenBSD: kexc25519c.c,v 1.4 2014/01/12 08:13:13 djm Exp $ */
/*
* Copyright (c) 2001 Markus Friedl. All rights reserved.
* Copyright (c) 2010 Damien Miller. All rights reserved.
@ -45,7 +45,6 @@
void
kexc25519_client(Kex *kex)
{
BIGNUM *shared_secret;
Key *server_host_key;
u_char client_key[CURVE25519_SIZE];
u_char client_pubkey[CURVE25519_SIZE];
@ -53,6 +52,7 @@ kexc25519_client(Kex *kex)
u_char *server_host_key_blob = NULL, *signature = NULL;
u_char *hash;
u_int slen, sbloblen, hashlen;
Buffer shared_secret;
kexc25519_keygen(client_key, client_pubkey);
@ -93,7 +93,8 @@ kexc25519_client(Kex *kex)
signature = packet_get_string(&slen);
packet_check_eom();
shared_secret = kexc25519_shared_key(client_key, server_pubkey);
buffer_init(&shared_secret);
kexc25519_shared_key(client_key, server_pubkey, &shared_secret);
/* calc and verify H */
kex_c25519_hash(
@ -105,7 +106,7 @@ kexc25519_client(Kex *kex)
server_host_key_blob, sbloblen,
client_pubkey,
server_pubkey,
shared_secret,
buffer_ptr(&shared_secret), buffer_len(&shared_secret),
&hash, &hashlen
);
free(server_host_key_blob);
@ -121,8 +122,8 @@ kexc25519_client(Kex *kex)
kex->session_id = xmalloc(kex->session_id_len);
memcpy(kex->session_id, hash, kex->session_id_len);
}
kex_derive_keys(kex, hash, hashlen, shared_secret);
BN_clear_free(shared_secret);
kex_derive_keys(kex, hash, hashlen,
buffer_ptr(&shared_secret), buffer_len(&shared_secret));
buffer_free(&shared_secret);
kex_finish(kex);
}

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@ -1,4 +1,4 @@
/* $OpenBSD: kexc25519s.c,v 1.3 2014/01/09 23:20:00 djm Exp $ */
/* $OpenBSD: kexc25519s.c,v 1.4 2014/01/12 08:13:13 djm Exp $ */
/*
* Copyright (c) 2001 Markus Friedl. All rights reserved.
* Copyright (c) 2010 Damien Miller. All rights reserved.
@ -42,7 +42,6 @@
void
kexc25519_server(Kex *kex)
{
BIGNUM *shared_secret;
Key *server_host_private, *server_host_public;
u_char *server_host_key_blob = NULL, *signature = NULL;
u_char server_key[CURVE25519_SIZE];
@ -50,6 +49,7 @@ kexc25519_server(Kex *kex)
u_char server_pubkey[CURVE25519_SIZE];
u_char *hash;
u_int slen, sbloblen, hashlen;
Buffer shared_secret;
/* generate private key */
kexc25519_keygen(server_key, server_pubkey);
@ -76,7 +76,8 @@ kexc25519_server(Kex *kex)
dump_digest("client public key:", client_pubkey, CURVE25519_SIZE);
#endif
shared_secret = kexc25519_shared_key(server_key, client_pubkey);
buffer_init(&shared_secret);
kexc25519_shared_key(server_key, client_pubkey, &shared_secret);
/* calc H */
key_to_blob(server_host_public, &server_host_key_blob, &sbloblen);
@ -89,7 +90,7 @@ kexc25519_server(Kex *kex)
server_host_key_blob, sbloblen,
client_pubkey,
server_pubkey,
shared_secret,
buffer_ptr(&shared_secret), buffer_len(&shared_secret),
&hash, &hashlen
);
@ -117,7 +118,9 @@ kexc25519_server(Kex *kex)
free(server_host_key_blob);
/* have keys, free server key */
free(client_pubkey);
kex_derive_keys(kex, hash, hashlen, shared_secret);
BN_clear_free(shared_secret);
kex_derive_keys(kex, hash, hashlen,
buffer_ptr(&shared_secret), buffer_len(&shared_secret));
buffer_free(&shared_secret);
kex_finish(kex);
}

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@ -1,4 +1,4 @@
/* $OpenBSD: kexdhc.c,v 1.13 2013/05/17 00:13:13 djm Exp $ */
/* $OpenBSD: kexdhc.c,v 1.14 2014/01/12 08:13:13 djm Exp $ */
/*
* Copyright (c) 2001 Markus Friedl. All rights reserved.
*
@ -155,7 +155,7 @@ kexdh_client(Kex *kex)
memcpy(kex->session_id, hash, kex->session_id_len);
}
kex_derive_keys(kex, hash, hashlen, shared_secret);
kex_derive_keys_bn(kex, hash, hashlen, shared_secret);
BN_clear_free(shared_secret);
kex_finish(kex);
}

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@ -1,4 +1,4 @@
/* $OpenBSD: kexdhs.c,v 1.16 2013/11/02 22:24:24 markus Exp $ */
/* $OpenBSD: kexdhs.c,v 1.17 2014/01/12 08:13:13 djm Exp $ */
/*
* Copyright (c) 2001 Markus Friedl. All rights reserved.
*
@ -154,7 +154,7 @@ kexdh_server(Kex *kex)
/* have keys, free DH */
DH_free(dh);
kex_derive_keys(kex, hash, hashlen, shared_secret);
kex_derive_keys_bn(kex, hash, hashlen, shared_secret);
BN_clear_free(shared_secret);
kex_finish(kex);
}

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@ -1,4 +1,4 @@
/* $OpenBSD: kexecdhc.c,v 1.5 2014/01/09 23:20:00 djm Exp $ */
/* $OpenBSD: kexecdhc.c,v 1.6 2014/01/12 08:13:13 djm Exp $ */
/*
* Copyright (c) 2001 Markus Friedl. All rights reserved.
* Copyright (c) 2010 Damien Miller. All rights reserved.
@ -152,7 +152,7 @@ kexecdh_client(Kex *kex)
memcpy(kex->session_id, hash, kex->session_id_len);
}
kex_derive_keys(kex, hash, hashlen, shared_secret);
kex_derive_keys_bn(kex, hash, hashlen, shared_secret);
BN_clear_free(shared_secret);
kex_finish(kex);
}

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@ -1,4 +1,4 @@
/* $OpenBSD: kexecdhs.c,v 1.8 2014/01/09 23:20:00 djm Exp $ */
/* $OpenBSD: kexecdhs.c,v 1.9 2014/01/12 08:13:13 djm Exp $ */
/*
* Copyright (c) 2001 Markus Friedl. All rights reserved.
* Copyright (c) 2010 Damien Miller. All rights reserved.
@ -148,7 +148,7 @@ kexecdh_server(Kex *kex)
/* have keys, free server key */
EC_KEY_free(server_key);
kex_derive_keys(kex, hash, hashlen, shared_secret);
kex_derive_keys_bn(kex, hash, hashlen, shared_secret);
BN_clear_free(shared_secret);
kex_finish(kex);
}

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@ -1,4 +1,4 @@
/* $OpenBSD: kexgexc.c,v 1.14 2014/01/09 23:20:00 djm Exp $ */
/* $OpenBSD: kexgexc.c,v 1.15 2014/01/12 08:13:13 djm Exp $ */
/*
* Copyright (c) 2000 Niels Provos. All rights reserved.
* Copyright (c) 2001 Markus Friedl. All rights reserved.
@ -200,7 +200,7 @@ kexgex_client(Kex *kex)
kex->session_id = xmalloc(kex->session_id_len);
memcpy(kex->session_id, hash, kex->session_id_len);
}
kex_derive_keys(kex, hash, hashlen, shared_secret);
kex_derive_keys_bn(kex, hash, hashlen, shared_secret);
BN_clear_free(shared_secret);
kex_finish(kex);

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@ -1,4 +1,4 @@
/* $OpenBSD: kexgexs.c,v 1.17 2014/01/09 23:20:00 djm Exp $ */
/* $OpenBSD: kexgexs.c,v 1.18 2014/01/12 08:13:13 djm Exp $ */
/*
* Copyright (c) 2000 Niels Provos. All rights reserved.
* Copyright (c) 2001 Markus Friedl. All rights reserved.
@ -201,7 +201,7 @@ kexgex_server(Kex *kex)
/* have keys, free DH */
DH_free(dh);
kex_derive_keys(kex, hash, hashlen, shared_secret);
kex_derive_keys_bn(kex, hash, hashlen, shared_secret);
BN_clear_free(shared_secret);
kex_finish(kex);