/* $OpenBSD: ssh-rsa.c,v 1.79 2023/03/05 05:34:09 dtucker 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 "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 u_int

ssh_rsa_size(const struct sshkey *key)

{

  const BIGNUM *rsa_n;

  if (key->rsa == NULL)

    return 0;

  RSA_get0_key(key->rsa, &rsa_n, NULL, NULL);

  return BN_num_bits(rsa_n);

}

static int

ssh_rsa_alloc(struct sshkey *k)

{

  if ((k->rsa = RSA_new()) == NULL)

    return SSH_ERR_ALLOC_FAIL;

  return 0;

}

static void

ssh_rsa_cleanup(struct sshkey *k)

{

  RSA_free(k->rsa);

  k->rsa = NULL;

}

static int

ssh_rsa_equal(const struct sshkey *a, const struct sshkey *b)

{

  const BIGNUM *rsa_e_a, *rsa_n_a;

  const BIGNUM *rsa_e_b, *rsa_n_b;

  if (a->rsa == NULL || b->rsa == NULL)

    return 0;

  RSA_get0_key(a->rsa, &rsa_n_a, &rsa_e_a, NULL);

  RSA_get0_key(b->rsa, &rsa_n_b, &rsa_e_b, NULL);

  if (rsa_e_a == NULL || rsa_e_b == NULL)

    return 0;

  if (rsa_n_a == NULL || rsa_n_b == NULL)

    return 0;

  if (BN_cmp(rsa_e_a, rsa_e_b) != 0)

    return 0;

  if (BN_cmp(rsa_n_a, rsa_n_b) != 0)

    return 0;

  return 1;

}

static int

ssh_rsa_serialize_public(const struct sshkey *key, struct sshbuf *b,

    enum sshkey_serialize_rep opts)

{

  int r;

  const BIGNUM *rsa_n, *rsa_e;

  if (key->rsa == NULL)

    return SSH_ERR_INVALID_ARGUMENT;

  RSA_get0_key(key->rsa, &rsa_n, &rsa_e, NULL);

  if ((r = sshbuf_put_bignum2(b, rsa_e)) != 0 ||

      (r = sshbuf_put_bignum2(b, rsa_n)) != 0)

    return r;

  return 0;

}

static int

ssh_rsa_serialize_private(const struct sshkey *key, struct sshbuf *b,

    enum sshkey_serialize_rep opts)

{

  int r;

  const BIGNUM *rsa_n, *rsa_e, *rsa_d, *rsa_iqmp, *rsa_p, *rsa_q;

  RSA_get0_key(key->rsa, &rsa_n, &rsa_e, &rsa_d);

  RSA_get0_factors(key->rsa, &rsa_p, &rsa_q);

  RSA_get0_crt_params(key->rsa, NULL, NULL, &rsa_iqmp);

  if (!sshkey_is_cert(key)) {

    /* Note: can't reuse ssh_rsa_serialize_public: e, n vs. n, e */

    if ((r = sshbuf_put_bignum2(b, rsa_n)) != 0 ||

        (r = sshbuf_put_bignum2(b, rsa_e)) != 0)

      return r;

  }

  if ((r = sshbuf_put_bignum2(b, rsa_d)) != 0 ||

      (r = sshbuf_put_bignum2(b, rsa_iqmp)) != 0 ||

      (r = sshbuf_put_bignum2(b, rsa_p)) != 0 ||

      (r = sshbuf_put_bignum2(b, rsa_q)) != 0)

    return r;

  return 0;

}

static int

ssh_rsa_generate(struct sshkey *k, int bits)

{

  RSA *private = NULL;

  BIGNUM *f4 = NULL;

  int ret = SSH_ERR_INTERNAL_ERROR;

  if (bits < SSH_RSA_MINIMUM_MODULUS_SIZE ||

      bits > SSHBUF_MAX_BIGNUM * 8)

    return SSH_ERR_KEY_LENGTH;

  if ((private = RSA_new()) == NULL || (f4 = BN_new()) == NULL) {

    ret = SSH_ERR_ALLOC_FAIL;

    goto out;

  }

  if (!BN_set_word(f4, RSA_F4) ||

      !RSA_generate_key_ex(private, bits, f4, NULL)) {

    ret = SSH_ERR_LIBCRYPTO_ERROR;

    goto out;

  }

  k->rsa = private;

  private = NULL;

  ret = 0;

 out:

  RSA_free(private);

  BN_free(f4);

  return ret;

}

static int

ssh_rsa_copy_public(const struct sshkey *from, struct sshkey *to)

{

  const BIGNUM *rsa_n, *rsa_e;

  BIGNUM *rsa_n_dup = NULL, *rsa_e_dup = NULL;

  int r = SSH_ERR_INTERNAL_ERROR;

  RSA_get0_key(from->rsa, &rsa_n, &rsa_e, NULL);

  if ((rsa_n_dup = BN_dup(rsa_n)) == NULL ||

      (rsa_e_dup = BN_dup(rsa_e)) == NULL) {

    r = SSH_ERR_ALLOC_FAIL;

    goto out;

  }

  if (!RSA_set0_key(to->rsa, rsa_n_dup, rsa_e_dup, NULL)) {

    r = SSH_ERR_LIBCRYPTO_ERROR;

    goto out;

  }

  rsa_n_dup = rsa_e_dup = NULL; /* transferred */

  /* success */

  r = 0;

 out:

  BN_clear_free(rsa_n_dup);

  BN_clear_free(rsa_e_dup);

  return r;

}

static int

ssh_rsa_deserialize_public(const char *ktype, struct sshbuf *b,

    struct sshkey *key)

{

  int ret = SSH_ERR_INTERNAL_ERROR;

  BIGNUM *rsa_n = NULL, *rsa_e = NULL;

  if (sshbuf_get_bignum2(b, &rsa_e) != 0 ||

      sshbuf_get_bignum2(b, &rsa_n) != 0) {

    ret = SSH_ERR_INVALID_FORMAT;

    goto out;

  }

  if (!RSA_set0_key(key->rsa, rsa_n, rsa_e, NULL)) {

    ret = SSH_ERR_LIBCRYPTO_ERROR;

    goto out;

  }

  rsa_n = rsa_e = NULL; /* transferred */

  if ((ret = sshkey_check_rsa_length(key, 0)) != 0)

    goto out;

#ifdef DEBUG_PK

  RSA_print_fp(stderr, key->rsa, 8);

#endif

  /* success */

  ret = 0;

 out:

  BN_clear_free(rsa_n);

  BN_clear_free(rsa_e);

  return ret;

}

static int

ssh_rsa_deserialize_private(const char *ktype, struct sshbuf *b,

    struct sshkey *key)

{

  int r;

  BIGNUM *rsa_n = NULL, *rsa_e = NULL, *rsa_d = NULL;

  BIGNUM *rsa_iqmp = NULL, *rsa_p = NULL, *rsa_q = NULL;

  /* Note: can't reuse ssh_rsa_deserialize_public: e, n vs. n, e */

  if (!sshkey_is_cert(key)) {

    if ((r = sshbuf_get_bignum2(b, &rsa_n)) != 0 ||

        (r = sshbuf_get_bignum2(b, &rsa_e)) != 0)

      goto out;

    if (!RSA_set0_key(key->rsa, rsa_n, rsa_e, NULL)) {

      r = SSH_ERR_LIBCRYPTO_ERROR;

      goto out;

    }

    rsa_n = rsa_e = NULL; /* transferred */

  }

  if ((r = sshbuf_get_bignum2(b, &rsa_d)) != 0 ||

      (r = sshbuf_get_bignum2(b, &rsa_iqmp)) != 0 ||

      (r = sshbuf_get_bignum2(b, &rsa_p)) != 0 ||

      (r = sshbuf_get_bignum2(b, &rsa_q)) != 0)

    goto out;

  if (!RSA_set0_key(key->rsa, NULL, NULL, rsa_d)) {

    r = SSH_ERR_LIBCRYPTO_ERROR;

    goto out;

  }

  rsa_d = NULL; /* transferred */

  if (!RSA_set0_factors(key->rsa, rsa_p, rsa_q)) {

    r = SSH_ERR_LIBCRYPTO_ERROR;

    goto out;

  }

  rsa_p = rsa_q = NULL; /* transferred */

  if ((r = sshkey_check_rsa_length(key, 0)) != 0)

    goto out;

  if ((r = ssh_rsa_complete_crt_parameters(key, rsa_iqmp)) != 0)

    goto out;

  if (RSA_blinding_on(key->rsa, NULL) != 1) {

    r = SSH_ERR_LIBCRYPTO_ERROR;

    goto out;

  }

  /* success */

  r = 0;

 out:

  BN_clear_free(rsa_n);

  BN_clear_free(rsa_e);

  BN_clear_free(rsa_d);

  BN_clear_free(rsa_p);

  BN_clear_free(rsa_q);

  BN_clear_free(rsa_iqmp);

  return r;

}

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 */

static int

ssh_rsa_sign(struct sshkey *key,

    u_char **sigp, size_t *lenp,

    const u_char *data, size_t datalen,

    const char *alg, const char *sk_provider, const char *sk_pin, u_int compat)

{

  const BIGNUM *rsa_n;

  u_char digest[SSH_DIGEST_MAX_LENGTH], *sig = NULL;

  size_t slen = 0;

  u_int hlen, 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 == NULL || strlen(alg) == 0)

    hash_alg = SSH_DIGEST_SHA1;

  else

    hash_alg = rsa_hash_id_from_keyname(alg);

  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 ((hlen = 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, hlen, 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;

}

static int

ssh_rsa_verify(const struct sshkey *key,

    const u_char *sig, size_t siglen,

    const u_char *data, size_t dlen, const char *alg, u_int compat,

    struct sshkey_sig_details **detailsp)

{

  const BIGNUM *rsa_n;

  char *sigtype = NULL;

  int hash_alg, want_alg, ret = SSH_ERR_INTERNAL_ERROR;

  size_t len = 0, diff, modlen, hlen;

  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 ((hlen = ssh_digest_bytes(hash_alg)) == 0) {

    ret = SSH_ERR_INTERNAL_ERROR;

    goto out;

  }

  if ((ret = ssh_digest_memory(hash_alg, data, dlen,

      digest, sizeof(digest))) != 0)

    goto out;

  ret = openssh_RSA_verify(hash_alg, digest, hlen, 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;

}

static const struct sshkey_impl_funcs sshkey_rsa_funcs = {

  /* .size = */   ssh_rsa_size,

  /* .alloc = */    ssh_rsa_alloc,

  /* .cleanup = */  ssh_rsa_cleanup,

  /* .equal = */    ssh_rsa_equal,

  /* .ssh_serialize_public = */ ssh_rsa_serialize_public,

  /* .ssh_deserialize_public = */ ssh_rsa_deserialize_public,

  /* .ssh_serialize_private = */ ssh_rsa_serialize_private,

  /* .ssh_deserialize_private = */ ssh_rsa_deserialize_private,

  /* .generate = */ ssh_rsa_generate,

  /* .copy_public = */  ssh_rsa_copy_public,

  /* .sign = */   ssh_rsa_sign,

  /* .verify = */   ssh_rsa_verify,

};

const struct sshkey_impl sshkey_rsa_impl = {

  /* .name = */   "ssh-rsa",

  /* .shortname = */  "RSA",

  /* .sigalg = */   NULL,

  /* .type = */   KEY_RSA,

  /* .nid = */    0,

  /* .cert = */   0,

  /* .sigonly = */  0,

  /* .keybits = */  0,

  /* .funcs = */    &sshkey_rsa_funcs,

};

const struct sshkey_impl sshkey_rsa_cert_impl = {

  /* .name = */   "ssh-rsa-cert-v01@openssh.com",

  /* .shortname = */  "RSA-CERT",

  /* .sigalg = */   NULL,

  /* .type = */   KEY_RSA_CERT,

  /* .nid = */    0,

  /* .cert = */   1,

  /* .sigonly = */  0,

  /* .keybits = */  0,

  /* .funcs = */    &sshkey_rsa_funcs,

};

/* SHA2 signature algorithms */

const struct sshkey_impl sshkey_rsa_sha256_impl = {

  /* .name = */   "rsa-sha2-256",

  /* .shortname = */  "RSA",

  /* .sigalg = */   NULL,

  /* .type = */   KEY_RSA,

  /* .nid = */    0,

  /* .cert = */   0,

  /* .sigonly = */  1,

  /* .keybits = */  0,

  /* .funcs = */    &sshkey_rsa_funcs,

};

const struct sshkey_impl sshkey_rsa_sha512_impl = {

  /* .name = */   "rsa-sha2-512",

  /* .shortname = */  "RSA",

  /* .sigalg = */   NULL,

  /* .type = */   KEY_RSA,

  /* .nid = */    0,

  /* .cert = */   0,

  /* .sigonly = */  1,

  /* .keybits = */  0,

  /* .funcs = */    &sshkey_rsa_funcs,

};

const struct sshkey_impl sshkey_rsa_sha256_cert_impl = {

  /* .name = */   "rsa-sha2-256-cert-v01@openssh.com",

  /* .shortname = */  "RSA-CERT",

  /* .sigalg = */   "rsa-sha2-256",

  /* .type = */   KEY_RSA_CERT,

  /* .nid = */    0,

  /* .cert = */   1,

  /* .sigonly = */  1,

  /* .keybits = */  0,

  /* .funcs = */    &sshkey_rsa_funcs,

};

const struct sshkey_impl sshkey_rsa_sha512_cert_impl = {

  /* .name = */   "rsa-sha2-512-cert-v01@openssh.com",

  /* .shortname = */  "RSA-CERT",

  /* .sigalg = */   "rsa-sha2-512",

  /* .type = */   KEY_RSA_CERT,

  /* .nid = */    0,

  /* .cert = */   1,

  /* .sigonly = */  1,

  /* .keybits = */  0,

  /* .funcs = */    &sshkey_rsa_funcs,

};

#endif /* WITH_OPENSSL */