source: trunk/third/openssh/ssh-rsa.c @ 18759

/*
 * Copyright (c) 2000 Markus Friedl.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "includes.h"
RCSID("$OpenBSD: ssh-rsa.c,v 1.26 2002/08/27 17:13:56 stevesk Exp $");

#include <openssl/evp.h>
#include <openssl/err.h>

#include "xmalloc.h"
#include "log.h"
#include "buffer.h"
#include "bufaux.h"
#include "key.h"
#include "ssh-rsa.h"
#include "compat.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(Key *key, u_char **sigp, u_int *lenp,
    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->type != KEY_RSA || key->rsa == NULL) {
                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(Key *key, u_char *signature, u_int signaturelen,
    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->type != KEY_RSA || key->rsa == NULL) {
                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_string(&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, 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;
        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;
                break;
        }
        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 != hlen + oidlen) {
                error("bad decrypted len: %d != %d + %d", len, hlen, oidlen);
                goto done;
        }
        if (memcmp(decrypted, oid, oidlen) != 0) {
                error("oid mismatch");
                goto done;
        }
        if (memcmp(decrypted + oidlen, hash, hlen) != 0) {
                error("hash mismatch");
                goto done;
        }
        ret = 1;
done:
        if (decrypted)
                xfree(decrypted);
        return ret;
}