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openssh/ssh-rsa.c

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/* $OpenBSD: ssh-rsa.c,v 1.67 2018/07/03 11:39:54 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"
#ifdef WITH_OPENSSL
#include <sys/types.h>
#include <openssl/evp.h>
#include <openssl/err.h>
#include <stdarg.h>
#include <string.h>
#include "sshbuf.h"
#include "compat.h"
#include "ssherr.h"
#define SSHKEY_INTERNAL
#include "sshkey.h"
#include "digest.h"
#include "log.h"
#include "openbsd-compat/openssl-compat.h"
static int openssh_RSA_verify(int, u_char *, size_t, u_char *, size_t, RSA *);
static const char *
rsa_hash_alg_ident(int hash_alg)
{
switch (hash_alg) {
case SSH_DIGEST_SHA1:
return "ssh-rsa";
case SSH_DIGEST_SHA256:
return "rsa-sha2-256";
case SSH_DIGEST_SHA512:
return "rsa-sha2-512";
}
return NULL;
}
/*
* Returns the hash algorithm ID for a given algorithm identifier as used
* inside the signature blob,
*/
static int
rsa_hash_id_from_ident(const char *ident)
{
if (strcmp(ident, "ssh-rsa") == 0)
return SSH_DIGEST_SHA1;
if (strcmp(ident, "rsa-sha2-256") == 0)
return SSH_DIGEST_SHA256;
if (strcmp(ident, "rsa-sha2-512") == 0)
return SSH_DIGEST_SHA512;
return -1;
}
/*
* Return the hash algorithm ID for the specified key name. This includes
* all the cases of rsa_hash_id_from_ident() but also the certificate key
* types.
*/
static int
rsa_hash_id_from_keyname(const char *alg)
{
int r;
if ((r = rsa_hash_id_from_ident(alg)) != -1)
return r;
if (strcmp(alg, "ssh-rsa-cert-v01@openssh.com") == 0)
return SSH_DIGEST_SHA1;
if (strcmp(alg, "rsa-sha2-256-cert-v01@openssh.com") == 0)
return SSH_DIGEST_SHA256;
if (strcmp(alg, "rsa-sha2-512-cert-v01@openssh.com") == 0)
return SSH_DIGEST_SHA512;
return -1;
}
static int
rsa_hash_alg_nid(int type)
{
switch (type) {
case SSH_DIGEST_SHA1:
return NID_sha1;
case SSH_DIGEST_SHA256:
return NID_sha256;
case SSH_DIGEST_SHA512:
return NID_sha512;
default:
return -1;
}
}
int
ssh_rsa_complete_crt_parameters(struct sshkey *key, const BIGNUM *iqmp)
{
const BIGNUM *rsa_p, *rsa_q, *rsa_d;
BIGNUM *aux = NULL, *d_consttime = NULL;
BIGNUM *rsa_dmq1 = NULL, *rsa_dmp1 = NULL, *rsa_iqmp = NULL;
BN_CTX *ctx = NULL;
int r;
if (key == NULL || key->rsa == NULL ||
sshkey_type_plain(key->type) != KEY_RSA)
return SSH_ERR_INVALID_ARGUMENT;
RSA_get0_key(key->rsa, NULL, NULL, &rsa_d);
RSA_get0_factors(key->rsa, &rsa_p, &rsa_q);
if ((ctx = BN_CTX_new()) == NULL)
return SSH_ERR_ALLOC_FAIL;
if ((aux = BN_new()) == NULL ||
(rsa_dmq1 = BN_new()) == NULL ||
(rsa_dmp1 = BN_new()) == NULL)
return SSH_ERR_ALLOC_FAIL;
if ((d_consttime = BN_dup(rsa_d)) == NULL ||
(rsa_iqmp = BN_dup(iqmp)) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
BN_set_flags(aux, BN_FLG_CONSTTIME);
BN_set_flags(d_consttime, BN_FLG_CONSTTIME);
if ((BN_sub(aux, rsa_q, BN_value_one()) == 0) ||
(BN_mod(rsa_dmq1, d_consttime, aux, ctx) == 0) ||
(BN_sub(aux, rsa_p, BN_value_one()) == 0) ||
(BN_mod(rsa_dmp1, d_consttime, aux, ctx) == 0)) {
r = SSH_ERR_LIBCRYPTO_ERROR;
goto out;
}
if (!RSA_set0_crt_params(key->rsa, rsa_dmp1, rsa_dmq1, rsa_iqmp)) {
r = SSH_ERR_LIBCRYPTO_ERROR;
goto out;
}
rsa_dmp1 = rsa_dmq1 = rsa_iqmp = NULL; /* transferred */
/* success */
r = 0;
out:
BN_clear_free(aux);
BN_clear_free(d_consttime);
BN_clear_free(rsa_dmp1);
BN_clear_free(rsa_dmq1);
BN_clear_free(rsa_iqmp);
BN_CTX_free(ctx);
return r;
}
/* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */
int
ssh_rsa_sign(const struct sshkey *key, u_char **sigp, size_t *lenp,
const u_char *data, size_t datalen, const char *alg_ident)
{
const BIGNUM *rsa_n;
u_char digest[SSH_DIGEST_MAX_LENGTH], *sig = NULL;
size_t slen = 0;
u_int dlen, len;
int nid, hash_alg, ret = SSH_ERR_INTERNAL_ERROR;
struct sshbuf *b = NULL;
if (lenp != NULL)
*lenp = 0;
if (sigp != NULL)
*sigp = NULL;
if (alg_ident == NULL || strlen(alg_ident) == 0)
hash_alg = SSH_DIGEST_SHA1;
else
hash_alg = rsa_hash_id_from_keyname(alg_ident);
if (key == NULL || key->rsa == NULL || hash_alg == -1 ||
sshkey_type_plain(key->type) != KEY_RSA)
return SSH_ERR_INVALID_ARGUMENT;
RSA_get0_key(key->rsa, &rsa_n, NULL, NULL);
if (BN_num_bits(rsa_n) < SSH_RSA_MINIMUM_MODULUS_SIZE)
return SSH_ERR_KEY_LENGTH;
slen = RSA_size(key->rsa);
if (slen <= 0 || slen > SSHBUF_MAX_BIGNUM)
return SSH_ERR_INVALID_ARGUMENT;
/* hash the data */
nid = rsa_hash_alg_nid(hash_alg);
if ((dlen = ssh_digest_bytes(hash_alg)) == 0)
return SSH_ERR_INTERNAL_ERROR;
if ((ret = ssh_digest_memory(hash_alg, data, datalen,
digest, sizeof(digest))) != 0)
goto out;
if ((sig = malloc(slen)) == NULL) {
ret = SSH_ERR_ALLOC_FAIL;
goto out;
}
if (RSA_sign(nid, digest, dlen, sig, &len, key->rsa) != 1) {
ret = SSH_ERR_LIBCRYPTO_ERROR;
goto out;
}
if (len < slen) {
size_t diff = slen - len;
memmove(sig + diff, sig, len);
explicit_bzero(sig, diff);
} else if (len > slen) {
ret = SSH_ERR_INTERNAL_ERROR;
goto out;
}
/* encode signature */
if ((b = sshbuf_new()) == NULL) {
ret = SSH_ERR_ALLOC_FAIL;
goto out;
}
if ((ret = sshbuf_put_cstring(b, rsa_hash_alg_ident(hash_alg))) != 0 ||
(ret = sshbuf_put_string(b, sig, slen)) != 0)
goto out;
len = sshbuf_len(b);
if (sigp != NULL) {
if ((*sigp = malloc(len)) == NULL) {
ret = SSH_ERR_ALLOC_FAIL;
goto out;
}
memcpy(*sigp, sshbuf_ptr(b), len);
}
if (lenp != NULL)
*lenp = len;
ret = 0;
out:
explicit_bzero(digest, sizeof(digest));
freezero(sig, slen);
sshbuf_free(b);
return ret;
}
int
ssh_rsa_verify(const struct sshkey *key,
const u_char *sig, size_t siglen, const u_char *data, size_t datalen,
const char *alg)
{
const BIGNUM *rsa_n;
char *sigtype = NULL;
int hash_alg, want_alg, ret = SSH_ERR_INTERNAL_ERROR;
size_t len = 0, diff, modlen, dlen;
struct sshbuf *b = NULL;
u_char digest[SSH_DIGEST_MAX_LENGTH], *osigblob, *sigblob = NULL;
if (key == NULL || key->rsa == NULL ||
sshkey_type_plain(key->type) != KEY_RSA ||
sig == NULL || siglen == 0)
return SSH_ERR_INVALID_ARGUMENT;
RSA_get0_key(key->rsa, &rsa_n, NULL, NULL);
if (BN_num_bits(rsa_n) < SSH_RSA_MINIMUM_MODULUS_SIZE)
return SSH_ERR_KEY_LENGTH;
if ((b = sshbuf_from(sig, siglen)) == NULL)
return SSH_ERR_ALLOC_FAIL;
if (sshbuf_get_cstring(b, &sigtype, NULL) != 0) {
ret = SSH_ERR_INVALID_FORMAT;
goto out;
}
if ((hash_alg = rsa_hash_id_from_ident(sigtype)) == -1) {
ret = SSH_ERR_KEY_TYPE_MISMATCH;
goto out;
}
/*
* Allow ssh-rsa-cert-v01 certs to generate SHA2 signatures for
* legacy reasons, but otherwise the signature type should match.
*/
if (alg != NULL && strcmp(alg, "ssh-rsa-cert-v01@openssh.com") != 0) {
if ((want_alg = rsa_hash_id_from_keyname(alg)) == -1) {
ret = SSH_ERR_INVALID_ARGUMENT;
goto out;
}
if (hash_alg != want_alg) {
ret = SSH_ERR_SIGNATURE_INVALID;
goto out;
}
}
if (sshbuf_get_string(b, &sigblob, &len) != 0) {
ret = SSH_ERR_INVALID_FORMAT;
goto out;
}
if (sshbuf_len(b) != 0) {
ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
goto out;
}
/* RSA_verify expects a signature of RSA_size */
modlen = RSA_size(key->rsa);
if (len > modlen) {
ret = SSH_ERR_KEY_BITS_MISMATCH;
goto out;
} else if (len < modlen) {
diff = modlen - len;
osigblob = sigblob;
if ((sigblob = realloc(sigblob, modlen)) == NULL) {
sigblob = osigblob; /* put it back for clear/free */
ret = SSH_ERR_ALLOC_FAIL;
goto out;
}
memmove(sigblob + diff, sigblob, len);
explicit_bzero(sigblob, diff);
len = modlen;
}
if ((dlen = ssh_digest_bytes(hash_alg)) == 0) {
ret = SSH_ERR_INTERNAL_ERROR;
goto out;
}
if ((ret = ssh_digest_memory(hash_alg, data, datalen,
digest, sizeof(digest))) != 0)
goto out;
ret = openssh_RSA_verify(hash_alg, digest, dlen, sigblob, len,
key->rsa);
out:
freezero(sigblob, len);
free(sigtype);
sshbuf_free(b);
explicit_bzero(digest, sizeof(digest));
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 */
};
/*
* See http://csrc.nist.gov/groups/ST/crypto_apps_infra/csor/algorithms.html
* id-sha256 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840)
* organization(1) gov(101) csor(3) nistAlgorithm(4) hashAlgs(2)
* id-sha256(1) }
*/
static const u_char id_sha256[] = {
0x30, 0x31, /* type Sequence, length 0x31 (49) */
0x30, 0x0d, /* type Sequence, length 0x0d (13) */
0x06, 0x09, /* type OID, length 0x09 */
0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, /* id-sha256 */
0x05, 0x00, /* NULL */
0x04, 0x20 /* Octet string, length 0x20 (32), followed by sha256 hash */
};
/*
* See http://csrc.nist.gov/groups/ST/crypto_apps_infra/csor/algorithms.html
* id-sha512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840)
* organization(1) gov(101) csor(3) nistAlgorithm(4) hashAlgs(2)
* id-sha256(3) }
*/
static const u_char id_sha512[] = {
0x30, 0x51, /* type Sequence, length 0x51 (81) */
0x30, 0x0d, /* type Sequence, length 0x0d (13) */
0x06, 0x09, /* type OID, length 0x09 */
0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03, /* id-sha512 */
0x05, 0x00, /* NULL */
0x04, 0x40 /* Octet string, length 0x40 (64), followed by sha512 hash */
};
static int
rsa_hash_alg_oid(int hash_alg, const u_char **oidp, size_t *oidlenp)
{
switch (hash_alg) {
case SSH_DIGEST_SHA1:
*oidp = id_sha1;
*oidlenp = sizeof(id_sha1);
break;
case SSH_DIGEST_SHA256:
*oidp = id_sha256;
*oidlenp = sizeof(id_sha256);
break;
case SSH_DIGEST_SHA512:
*oidp = id_sha512;
*oidlenp = sizeof(id_sha512);
break;
default:
return SSH_ERR_INVALID_ARGUMENT;
}
return 0;
}
static int
openssh_RSA_verify(int hash_alg, u_char *hash, size_t hashlen,
u_char *sigbuf, size_t siglen, RSA *rsa)
{
size_t rsasize = 0, oidlen = 0, hlen = 0;
int ret, len, oidmatch, hashmatch;
const u_char *oid = NULL;
u_char *decrypted = NULL;
if ((ret = rsa_hash_alg_oid(hash_alg, &oid, &oidlen)) != 0)
return ret;
ret = SSH_ERR_INTERNAL_ERROR;
hlen = ssh_digest_bytes(hash_alg);
if (hashlen != hlen) {
ret = SSH_ERR_INVALID_ARGUMENT;
goto done;
}
rsasize = RSA_size(rsa);
if (rsasize <= 0 || rsasize > SSHBUF_MAX_BIGNUM ||
siglen == 0 || siglen > rsasize) {
ret = SSH_ERR_INVALID_ARGUMENT;
goto done;
}
if ((decrypted = malloc(rsasize)) == NULL) {
ret = SSH_ERR_ALLOC_FAIL;
goto done;
}
if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa,
RSA_PKCS1_PADDING)) < 0) {
ret = SSH_ERR_LIBCRYPTO_ERROR;
goto done;
}
if (len < 0 || (size_t)len != hlen + oidlen) {
ret = SSH_ERR_INVALID_FORMAT;
goto done;
}
oidmatch = timingsafe_bcmp(decrypted, oid, oidlen) == 0;
hashmatch = timingsafe_bcmp(decrypted + oidlen, hash, hlen) == 0;
if (!oidmatch || !hashmatch) {
ret = SSH_ERR_SIGNATURE_INVALID;
goto done;
}
ret = 0;
done:
freezero(decrypted, rsasize);
return ret;
}
#endif /* WITH_OPENSSL */
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