rsa_sign.c

/*
 * Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
 *
 * Licensed under the OpenSSL license (the "License").  You may not use
 * this file except in compliance with the License.  You can obtain a copy
 * in the file LICENSE in the source distribution or at
 * https://www.openssl.org/source/license.html
 */

#include <stdio.h>
#include "internal/cryptlib.h"
#include <openssl/bn.h>
#include <openssl/rsa.h>
#include <openssl/objects.h>
#include <openssl/x509.h>
#include "crypto/x509.h"
#include "rsa_local.h"

/* Size of an SSL signature: MD5+SHA1 */
#define SSL_SIG_LENGTH  36

/*
 * encode_pkcs1 encodes a DigestInfo prefix of hash |type| and digest |m|, as
 * described in EMSA-PKCS1-v1_5-ENCODE, RFC 3447 section 9.2 step 2. This
 * encodes the DigestInfo (T and tLen) but does not add the padding.
 *
 * On success, it returns one and sets |*out| to a newly allocated buffer
 * containing the result and |*out_len| to its length. The caller must free
 * |*out| with |OPENSSL_free|. Otherwise, it returns zero.
 */
static int encode_pkcs1(unsigned char **out, int *out_len, int type,
                        const unsigned char *m, unsigned int m_len)
{
    X509_SIG sig;
    X509_ALGOR algor;
    ASN1_TYPE parameter;
    ASN1_OCTET_STRING digest;
    uint8_t *der = NULL;
    int len;

    sig.algor = &algor;
    sig.algor->algorithm = OBJ_nid2obj(type);
    if (sig.algor->algorithm == NULL) {
        RSAerr(RSA_F_ENCODE_PKCS1, RSA_R_UNKNOWN_ALGORITHM_TYPE);
        return 0;
    }
    if (OBJ_length(sig.algor->algorithm) == 0) {
        RSAerr(RSA_F_ENCODE_PKCS1,
               RSA_R_THE_ASN1_OBJECT_IDENTIFIER_IS_NOT_KNOWN_FOR_THIS_MD);
        return 0;
    }
    parameter.type = V_ASN1_NULL;
    parameter.value.ptr = NULL;
    sig.algor->parameter = &parameter;

    sig.digest = &digest;
    sig.digest->data = (unsigned char *)m;
    sig.digest->length = m_len;

    len = i2d_X509_SIG(&sig, &der);
    if (len < 0)
        return 0;

    *out = der;
    *out_len = len;
    return 1;
}

int RSA_sign(int type, const unsigned char *m, unsigned int m_len,
             unsigned char *sigret, unsigned int *siglen, RSA *rsa)
{
    int encrypt_len, encoded_len = 0, ret = 0;
    unsigned char *tmps = NULL;
    const unsigned char *encoded = NULL;

    if (rsa->meth->rsa_sign) {
        return rsa->meth->rsa_sign(type, m, m_len, sigret, siglen, rsa);
    }

    /* Compute the encoded digest. */
    if (type == NID_md5_sha1) {
        /*
         * NID_md5_sha1 corresponds to the MD5/SHA1 combination in TLS 1.1 and
         * earlier. It has no DigestInfo wrapper but otherwise is
         * RSASSA-PKCS1-v1_5.
         */
        if (m_len != SSL_SIG_LENGTH) {
            RSAerr(RSA_F_RSA_SIGN, RSA_R_INVALID_MESSAGE_LENGTH);
            return 0;
        }
        encoded_len = SSL_SIG_LENGTH;
        encoded = m;
    } else {
        if (!encode_pkcs1(&tmps, &encoded_len, type, m, m_len))
            goto err;
        encoded = tmps;
    }

    if (encoded_len > RSA_size(rsa) - RSA_PKCS1_PADDING_SIZE) {
        RSAerr(RSA_F_RSA_SIGN, RSA_R_DIGEST_TOO_BIG_FOR_RSA_KEY);
        goto err;
    }
    encrypt_len = RSA_private_encrypt(encoded_len, encoded, sigret, rsa,
                                      RSA_PKCS1_PADDING);
    if (encrypt_len <= 0)
        goto err;

    *siglen = encrypt_len;
    ret = 1;

err:
    OPENSSL_clear_free(tmps, (size_t)encoded_len);
    return ret;
}

/*
 * int_rsa_verify verifies an RSA signature in |sigbuf| using |rsa|. It may be
 * called in two modes. If |rm| is NULL, it verifies the signature for digest
 * |m|. Otherwise, it recovers the digest from the signature, writing the digest
 * to |rm| and the length to |*prm_len|. |type| is the NID of the digest
 * algorithm to use. It returns one on successful verification and zero
 * otherwise.
 */
int int_rsa_verify(int type, const unsigned char *m, unsigned int m_len,
                   unsigned char *rm, size_t *prm_len,
                   const unsigned char *sigbuf, size_t siglen, RSA *rsa)
{
    int decrypt_len, ret = 0, encoded_len = 0;
    unsigned char *decrypt_buf = NULL, *encoded = NULL;

    if (siglen != (size_t)RSA_size(rsa)) {
        RSAerr(RSA_F_INT_RSA_VERIFY, RSA_R_WRONG_SIGNATURE_LENGTH);
        return 0;
    }

    /* Recover the encoded digest. */
    decrypt_buf = OPENSSL_malloc(siglen);
    if (decrypt_buf == NULL) {
        RSAerr(RSA_F_INT_RSA_VERIFY, ERR_R_MALLOC_FAILURE);
        goto err;
    }

    decrypt_len = RSA_public_decrypt((int)siglen, sigbuf, decrypt_buf, rsa,
                                     RSA_PKCS1_PADDING);
    if (decrypt_len <= 0)
        goto err;

    if (type == NID_md5_sha1) {
        /*
         * NID_md5_sha1 corresponds to the MD5/SHA1 combination in TLS 1.1 and
         * earlier. It has no DigestInfo wrapper but otherwise is
         * RSASSA-PKCS1-v1_5.
         */
        if (decrypt_len != SSL_SIG_LENGTH) {
            RSAerr(RSA_F_INT_RSA_VERIFY, RSA_R_BAD_SIGNATURE);
            goto err;
        }

        if (rm != NULL) {
            memcpy(rm, decrypt_buf, SSL_SIG_LENGTH);
            *prm_len = SSL_SIG_LENGTH;
        } else {
            if (m_len != SSL_SIG_LENGTH) {
                RSAerr(RSA_F_INT_RSA_VERIFY, RSA_R_INVALID_MESSAGE_LENGTH);
                goto err;
            }

            if (memcmp(decrypt_buf, m, SSL_SIG_LENGTH) != 0) {
                RSAerr(RSA_F_INT_RSA_VERIFY, RSA_R_BAD_SIGNATURE);
                goto err;
            }
        }
    } else if (type == NID_mdc2 && decrypt_len == 2 + 16
               && decrypt_buf[0] == 0x04 && decrypt_buf[1] == 0x10) {
        /*
         * Oddball MDC2 case: signature can be OCTET STRING. check for correct
         * tag and length octets.
         */
        if (rm != NULL) {
            memcpy(rm, decrypt_buf + 2, 16);
            *prm_len = 16;
        } else {
            if (m_len != 16) {
                RSAerr(RSA_F_INT_RSA_VERIFY, RSA_R_INVALID_MESSAGE_LENGTH);
                goto err;
            }

            if (memcmp(m, decrypt_buf + 2, 16) != 0) {
                RSAerr(RSA_F_INT_RSA_VERIFY, RSA_R_BAD_SIGNATURE);
                goto err;
            }
        }
    } else {
        /*
         * If recovering the digest, extract a digest-sized output from the end
         * of |decrypt_buf| for |encode_pkcs1|, then compare the decryption
         * output as in a standard verification.
         */
        if (rm != NULL) {
            const EVP_MD *md = EVP_get_digestbynid(type);
            if (md == NULL) {
                RSAerr(RSA_F_INT_RSA_VERIFY, RSA_R_UNKNOWN_ALGORITHM_TYPE);
                goto err;
            }

            m_len = EVP_MD_size(md);
            if (m_len > (size_t)decrypt_len) {
                RSAerr(RSA_F_INT_RSA_VERIFY, RSA_R_INVALID_DIGEST_LENGTH);
                goto err;
            }
            m = decrypt_buf + decrypt_len - m_len;
        }

        /* Construct the encoded digest and ensure it matches. */
        if (!encode_pkcs1(&encoded, &encoded_len, type, m, m_len))
            goto err;

        if (encoded_len != decrypt_len
            || memcmp(encoded, decrypt_buf, encoded_len) != 0) {
            RSAerr(RSA_F_INT_RSA_VERIFY, RSA_R_BAD_SIGNATURE);
            goto err;
        }

        /* Output the recovered digest. */
        if (rm != NULL) {
            memcpy(rm, m, m_len);
            *prm_len = m_len;
        }
    }

    ret = 1;

err:
    OPENSSL_clear_free(encoded, (size_t)encoded_len);
    OPENSSL_clear_free(decrypt_buf, siglen);
    return ret;
}

int RSA_verify(int type, const unsigned char *m, unsigned int m_len,
               const unsigned char *sigbuf, unsigned int siglen, RSA *rsa)
{

    if (rsa->meth->rsa_verify) {
        return rsa->meth->rsa_verify(type, m, m_len, sigbuf, siglen, rsa);
    }

    return int_rsa_verify(type, m, m_len, NULL, NULL, sigbuf, siglen, rsa);
}