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openssh/ssh-rsa.c
Damien Miller da108ece68 - djm@cvs.openbsd.org 2010/08/31 09:58:37 
[auth-options.c auth1.c auth2.c bufaux.c buffer.h kex.c key.c packet.c]
     [packet.h ssh-dss.c ssh-rsa.c]
     Add buffer_get_cstring() and related functions that verify that the
     string extracted from the buffer contains no embedded \0 characters*
     This prevents random (possibly malicious) crap from being appended to
     strings where it would not be noticed if the string is used with
     a string(3) function.

     Use the new API in a few sensitive places.

     * actually, we allow a single one at the end of the string for now because
     we don't know how many deployed implementations get this wrong, but don't
     count on this to remain indefinitely.
2010-08-31 22:36:39 +10:00

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/* $OpenBSD: ssh-rsa.c,v 1.45 2010/08/31 09:58:37 djm Exp $ */
/*
* Copyright (c) 2000, 2003 Markus Friedl <markus@openbsd.org>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include "includes.h"
#include <sys/types.h>
#include <openssl/evp.h>
#include <openssl/err.h>
#include <stdarg.h>
#include <string.h>
#include "xmalloc.h"
#include "log.h"
#include "buffer.h"
#include "key.h"
#include "compat.h"
#include "misc.h"
#include "ssh.h"
static int openssh_RSA_verify(int, u_char *, u_int, u_char *, u_int, RSA *);
/* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */
int
ssh_rsa_sign(const Key *key, u_char **sigp, u_int *lenp,
const u_char *data, u_int datalen)
{
const EVP_MD *evp_md;
EVP_MD_CTX md;
u_char digest[EVP_MAX_MD_SIZE], *sig;
u_int slen, dlen, len;
int ok, nid;
Buffer b;
if (key == NULL || key->rsa == NULL || (key->type != KEY_RSA &&
key->type != KEY_RSA_CERT && key->type != KEY_RSA_CERT_V00)) {
error("ssh_rsa_sign: no RSA key");
return -1;
}
nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
error("ssh_rsa_sign: EVP_get_digestbynid %d failed", nid);
return -1;
}
EVP_DigestInit(&md, evp_md);
EVP_DigestUpdate(&md, data, datalen);
EVP_DigestFinal(&md, digest, &dlen);
slen = RSA_size(key->rsa);
sig = xmalloc(slen);
ok = RSA_sign(nid, digest, dlen, sig, &len, key->rsa);
memset(digest, 'd', sizeof(digest));
if (ok != 1) {
int ecode = ERR_get_error();
error("ssh_rsa_sign: RSA_sign failed: %s",
ERR_error_string(ecode, NULL));
xfree(sig);
return -1;
}
if (len < slen) {
u_int diff = slen - len;
debug("slen %u > len %u", slen, len);
memmove(sig + diff, sig, len);
memset(sig, 0, diff);
} else if (len > slen) {
error("ssh_rsa_sign: slen %u slen2 %u", slen, len);
xfree(sig);
return -1;
}
/* encode signature */
buffer_init(&b);
buffer_put_cstring(&b, "ssh-rsa");
buffer_put_string(&b, sig, slen);
len = buffer_len(&b);
if (lenp != NULL)
*lenp = len;
if (sigp != NULL) {
*sigp = xmalloc(len);
memcpy(*sigp, buffer_ptr(&b), len);
}
buffer_free(&b);
memset(sig, 's', slen);
xfree(sig);
return 0;
}
int
ssh_rsa_verify(const Key *key, const u_char *signature, u_int signaturelen,
const u_char *data, u_int datalen)
{
Buffer b;
const EVP_MD *evp_md;
EVP_MD_CTX md;
char *ktype;
u_char digest[EVP_MAX_MD_SIZE], *sigblob;
u_int len, dlen, modlen;
int rlen, ret, nid;
if (key == NULL || key->rsa == NULL || (key->type != KEY_RSA &&
key->type != KEY_RSA_CERT && key->type != KEY_RSA_CERT_V00)) {
error("ssh_rsa_verify: no RSA key");
return -1;
}
if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) {
error("ssh_rsa_verify: RSA modulus too small: %d < minimum %d bits",
BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE);
return -1;
}
buffer_init(&b);
buffer_append(&b, signature, signaturelen);
ktype = buffer_get_cstring(&b, NULL);
if (strcmp("ssh-rsa", ktype) != 0) {
error("ssh_rsa_verify: cannot handle type %s", ktype);
buffer_free(&b);
xfree(ktype);
return -1;
}
xfree(ktype);
sigblob = buffer_get_string(&b, &len);
rlen = buffer_len(&b);
buffer_free(&b);
if (rlen != 0) {
error("ssh_rsa_verify: remaining bytes in signature %d", rlen);
xfree(sigblob);
return -1;
}
/* RSA_verify expects a signature of RSA_size */
modlen = RSA_size(key->rsa);
if (len > modlen) {
error("ssh_rsa_verify: len %u > modlen %u", len, modlen);
xfree(sigblob);
return -1;
} else if (len < modlen) {
u_int diff = modlen - len;
debug("ssh_rsa_verify: add padding: modlen %u > len %u",
modlen, len);
sigblob = xrealloc(sigblob, 1, modlen);
memmove(sigblob + diff, sigblob, len);
memset(sigblob, 0, diff);
len = modlen;
}
nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
error("ssh_rsa_verify: EVP_get_digestbynid %d failed", nid);
xfree(sigblob);
return -1;
}
EVP_DigestInit(&md, evp_md);
EVP_DigestUpdate(&md, data, datalen);
EVP_DigestFinal(&md, digest, &dlen);
ret = openssh_RSA_verify(nid, digest, dlen, sigblob, len, key->rsa);
memset(digest, 'd', sizeof(digest));
memset(sigblob, 's', len);
xfree(sigblob);
debug("ssh_rsa_verify: signature %scorrect", (ret==0) ? "in" : "");
return ret;
}
/*
* See:
* http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/
* ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn
*/
/*
* id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
* oiw(14) secsig(3) algorithms(2) 26 }
*/
static const u_char id_sha1[] = {
0x30, 0x21, /* type Sequence, length 0x21 (33) */
0x30, 0x09, /* type Sequence, length 0x09 */
0x06, 0x05, /* type OID, length 0x05 */
0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */
0x05, 0x00, /* NULL */
0x04, 0x14 /* Octet string, length 0x14 (20), followed by sha1 hash */
};
/*
* id-md5 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
* rsadsi(113549) digestAlgorithm(2) 5 }
*/
static const u_char id_md5[] = {
0x30, 0x20, /* type Sequence, length 0x20 (32) */
0x30, 0x0c, /* type Sequence, length 0x09 */
0x06, 0x08, /* type OID, length 0x05 */
0x2a, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* id-md5 */
0x05, 0x00, /* NULL */
0x04, 0x10 /* Octet string, length 0x10 (16), followed by md5 hash */
};
static int
openssh_RSA_verify(int type, u_char *hash, u_int hashlen,
u_char *sigbuf, u_int siglen, RSA *rsa)
{
u_int ret, rsasize, oidlen = 0, hlen = 0;
int len, oidmatch, hashmatch;
const u_char *oid = NULL;
u_char *decrypted = NULL;
ret = 0;
switch (type) {
case NID_sha1:
oid = id_sha1;
oidlen = sizeof(id_sha1);
hlen = 20;
break;
case NID_md5:
oid = id_md5;
oidlen = sizeof(id_md5);
hlen = 16;
break;
default:
goto done;
}
if (hashlen != hlen) {
error("bad hashlen");
goto done;
}
rsasize = RSA_size(rsa);
if (siglen == 0 || siglen > rsasize) {
error("bad siglen");
goto done;
}
decrypted = xmalloc(rsasize);
if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa,
RSA_PKCS1_PADDING)) < 0) {
error("RSA_public_decrypt failed: %s",
ERR_error_string(ERR_get_error(), NULL));
goto done;
}
if (len < 0 || (u_int)len != hlen + oidlen) {
error("bad decrypted len: %d != %d + %d", len, hlen, oidlen);
goto done;
}
oidmatch = timingsafe_bcmp(decrypted, oid, oidlen) == 0;
hashmatch = timingsafe_bcmp(decrypted + oidlen, hash, hlen) == 0;
if (!oidmatch) {
error("oid mismatch");
goto done;
}
if (!hashmatch) {
error("hash mismatch");
goto done;
}
ret = 1;
done:
if (decrypted)
xfree(decrypted);
return ret;
}
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