text: /* $OpenBSD: ssh-rsa.c,v 1.60 2016/09/12 23:39:34 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"
  
  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;
  }
  
  static int
  rsa_hash_alg_from_ident(const char *ident)
  {
  	if (strcmp(ident, "ssh-rsa") == 0 ||
  	    strcmp(ident, "ssh-rsa-cert-v01@openssh.com") == 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;
  }
  
  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;
  	}
  }
  
  /* 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;
  	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_alg_from_ident(alg_ident);
  	if (key == NULL || key->rsa == NULL || hash_alg == -1 ||
  	    sshkey_type_plain(key->type) != KEY_RSA ||
  	    BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE)
  		return SSH_ERR_INVALID_ARGUMENT;
  	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));
  	if (sig != NULL) {
  		explicit_bzero(sig, slen);
  		free(sig);
  	}
  	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)
  {
  	char *ktype = NULL;
  	int hash_alg, ret = SSH_ERR_INTERNAL_ERROR;
  	size_t len, 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 ||
  	    BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE ||
  	    sig == NULL || siglen == 0)
  		return SSH_ERR_INVALID_ARGUMENT;
  
  	if ((b = sshbuf_from(sig, siglen)) == NULL)
  		return SSH_ERR_ALLOC_FAIL;
  	if (sshbuf_get_cstring(b, &ktype, NULL) != 0) {
  		ret = SSH_ERR_INVALID_FORMAT;
  		goto out;
  	}
  	if ((hash_alg = rsa_hash_alg_from_ident(ktype)) == -1) {
  		ret = SSH_ERR_KEY_TYPE_MISMATCH;
  		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:
  	if (sigblob != NULL) {
  		explicit_bzero(sigblob, len);
  		free(sigblob);
  	}
  	free(ktype);
  	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:
  	if (decrypted) {
  		explicit_bzero(decrypted, rsasize);
  		free(decrypted);
  	}
  	return ret;
  }
  #endif /* WITH_OPENSSL */
  