ssh-rsa.c - third_party/openssh-portable - Git at Google

 /* $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"

 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_generate_additional_parameters(struct sshkey *key)
 {
 	BIGNUM *aux = NULL;
 	BN_CTX *ctx = NULL;
 	BIGNUM d;
         BIGNUM *dptr;
 	int r;

 	if (key == NULL || key->rsa == NULL ||
 	    sshkey_type_plain(key->type) != KEY_RSA)
 		return SSH_ERR_INVALID_ARGUMENT;

 	if ((ctx = BN_CTX_new()) == NULL)
 		return SSH_ERR_ALLOC_FAIL;
 	if ((aux = BN_new()) == NULL) {
 		r = SSH_ERR_ALLOC_FAIL;
 		goto out;
 	}
 #ifdef BN_FLG_CONSTTIME
 	BN_set_flags(aux, BN_FLG_CONSTTIME);
 #endif

 	BN_init(&d);
 #ifdef BN_FLG_CONSTTIME
 	BN_with_flags(&d, key->rsa->d, BN_FLG_CONSTTIME);
         dptr = &d;
 #else
         dptr = key->rsa->d;
 #endif

 	if ((BN_sub(aux, key->rsa->q, BN_value_one()) == 0) ||
 	    (BN_mod(key->rsa->dmq1, dptr, aux, ctx) == 0) ||
 	    (BN_sub(aux, key->rsa->p, BN_value_one()) == 0) ||
 	    (BN_mod(key->rsa->dmp1, dptr, aux, ctx) == 0)) {
 		r = SSH_ERR_LIBCRYPTO_ERROR;
 		goto out;
 	}
 	r = 0;
  out:
 	BN_clear_free(aux);
 	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)
 {
 	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;
 	if (BN_num_bits(key->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)
 {
 	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;
 	if (BN_num_bits(key->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 */
	/* $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"

	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_generate_additional_parameters(struct sshkey *key)
	{
	BIGNUM *aux = NULL;
	BN_CTX *ctx = NULL;
	BIGNUM d;
	BIGNUM *dptr;
	int r;

	if (key == NULL \|\| key->rsa == NULL \|\|
	sshkey_type_plain(key->type) != KEY_RSA)
	return SSH_ERR_INVALID_ARGUMENT;

	if ((ctx = BN_CTX_new()) == NULL)
	return SSH_ERR_ALLOC_FAIL;
	if ((aux = BN_new()) == NULL) {
	r = SSH_ERR_ALLOC_FAIL;
	goto out;
	}
	#ifdef BN_FLG_CONSTTIME
	BN_set_flags(aux, BN_FLG_CONSTTIME);
	#endif

	BN_init(&d);
	#ifdef BN_FLG_CONSTTIME
	BN_with_flags(&d, key->rsa->d, BN_FLG_CONSTTIME);
	dptr = &d;
	#else
	dptr = key->rsa->d;
	#endif

	if ((BN_sub(aux, key->rsa->q, BN_value_one()) == 0) \|\|
	(BN_mod(key->rsa->dmq1, dptr, aux, ctx) == 0) \|\|
	(BN_sub(aux, key->rsa->p, BN_value_one()) == 0) \|\|
	(BN_mod(key->rsa->dmp1, dptr, aux, ctx) == 0)) {
	r = SSH_ERR_LIBCRYPTO_ERROR;
	goto out;
	}
	r = 0;
	out:
	BN_clear_free(aux);
	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)
	{
	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;
	if (BN_num_bits(key->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)
	{
	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;
	if (BN_num_bits(key->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 */