crypto/rsa/rsa_pk1.c

/*
 * Copyright 1995-2017 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 "internal/constant_time_locl.h"

#include <stdio.h>
#include "internal/cryptlib.h"
#include <openssl/bn.h>
#include <openssl/rsa.h>
#include <openssl/rand.h>

int RSA_padding_add_PKCS1_type_1(unsigned char *to, int tlen,
                                 const unsigned char *from, int flen)
{
    int j;
    unsigned char *p;

    if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {
        RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_TYPE_1,
               RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
        return 0;
    }

    p = (unsigned char *)to;

    *(p++) = 0;
    *(p++) = 1;                 /* Private Key BT (Block Type) */

    /* pad out with 0xff data */
    j = tlen - 3 - flen;
    memset(p, 0xff, j);
    p += j;
    *(p++) = '\0';
    memcpy(p, from, (unsigned int)flen);
    return 1;
}

int RSA_padding_check_PKCS1_type_1(unsigned char *to, int tlen,
                                   const unsigned char *from, int flen,
                                   int num)
{
    int i, j;
    const unsigned char *p;

    p = from;

    /*
     * The format is
     * 00 || 01 || PS || 00 || D
     * PS - padding string, at least 8 bytes of FF
     * D  - data.
     */

    if (num < 11)
        return -1;

    /* Accept inputs with and without the leading 0-byte. */
    if (num == flen) {
        if ((*p++) != 0x00) {
            RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
                   RSA_R_INVALID_PADDING);
            return -1;
        }
        flen--;
    }

    if ((num != (flen + 1)) || (*(p++) != 0x01)) {
        RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
               RSA_R_BLOCK_TYPE_IS_NOT_01);
        return -1;
    }

    /* scan over padding data */
    j = flen - 1;               /* one for type. */
    for (i = 0; i < j; i++) {
        if (*p != 0xff) {       /* should decrypt to 0xff */
            if (*p == 0) {
                p++;
                break;
            } else {
                RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
                       RSA_R_BAD_FIXED_HEADER_DECRYPT);
                return -1;
            }
        }
        p++;
    }

    if (i == j) {
        RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
               RSA_R_NULL_BEFORE_BLOCK_MISSING);
        return -1;
    }

    if (i < 8) {
        RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
               RSA_R_BAD_PAD_BYTE_COUNT);
        return -1;
    }
    i++;                        /* Skip over the '\0' */
    j -= i;
    if (j > tlen) {
        RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1, RSA_R_DATA_TOO_LARGE);
        return -1;
    }
    memcpy(to, p, (unsigned int)j);

    return j;
}

int RSA_padding_add_PKCS1_type_2(unsigned char *to, int tlen,
                                 const unsigned char *from, int flen)
{
    int i, j;
    unsigned char *p;

    if (flen > (tlen - 11)) {
        RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_TYPE_2,
               RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
        return 0;
    }

    p = (unsigned char *)to;

    *(p++) = 0;
    *(p++) = 2;                 /* Public Key BT (Block Type) */

    /* pad out with non-zero random data */
    j = tlen - 3 - flen;

    if (RAND_bytes(p, j) <= 0)
        return 0;
    for (i = 0; i < j; i++) {
        if (*p == '\0')
            do {
                if (RAND_bytes(p, 1) <= 0)
                    return 0;
            } while (*p == '\0');
        p++;
    }

    *(p++) = '\0';

    memcpy(p, from, (unsigned int)flen);
    return 1;
}

int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen,
                                   const unsigned char *from, int flen,
                                   int num)
{
    int i;
    /* |em| is the encoded message, zero-padded to exactly |num| bytes */
    unsigned char *em = NULL;
    unsigned int good, found_zero_byte;
    int zero_index = 0, msg_index, mlen = -1;

    if (tlen < 0 || flen < 0)
        return -1;

    /*
     * PKCS#1 v1.5 decryption. See "PKCS #1 v2.2: RSA Cryptography Standard",
     * section 7.2.2.
     */

    if (flen > num)
        goto err;

    if (num < 11)
        goto err;

    em = OPENSSL_zalloc(num);
    if (em == NULL) {
        RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, ERR_R_MALLOC_FAILURE);
        return -1;
    }
    /*
     * Always do this zero-padding copy (even when num == flen) to avoid
     * leaking that information. The copy still leaks some side-channel
     * information, but it's impossible to have a fixed memory access
     * pattern since we can't read out of the bounds of |from|.
     *
     * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
     */
    memcpy(em + num - flen, from, flen);

    good = constant_time_is_zero(em[0]);
    good &= constant_time_eq(em[1], 2);

    found_zero_byte = 0;
    for (i = 2; i < num; i++) {
        unsigned int equals0 = constant_time_is_zero(em[i]);
        zero_index =
            constant_time_select_int(~found_zero_byte & equals0, i,
                                     zero_index);
        found_zero_byte |= equals0;
    }

    /*
     * PS must be at least 8 bytes long, and it starts two bytes into |em|.
     * If we never found a 0-byte, then |zero_index| is 0 and the check
     * also fails.
     */
    good &= constant_time_ge((unsigned int)(zero_index), 2 + 8);

    /*
     * Skip the zero byte. This is incorrect if we never found a zero-byte
     * but in this case we also do not copy the message out.
     */
    msg_index = zero_index + 1;
    mlen = num - msg_index;

    /*
     * For good measure, do this check in constant time as well; it could
     * leak something if |tlen| was assuming valid padding.
     */
    good &= constant_time_ge((unsigned int)(tlen), (unsigned int)(mlen));

    /*
     * We can't continue in constant-time because we need to copy the result
     * and we cannot fake its length. This unavoidably leaks timing
     * information at the API boundary.
     */
    if (!good) {
        mlen = -1;
        goto err;
    }

    memcpy(to, em + msg_index, mlen);

 err:
    OPENSSL_clear_free(em, num);
    if (mlen == -1)
        RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,
               RSA_R_PKCS_DECODING_ERROR);
    return mlen;
}