openssl/crypto/rsa/rsa_pk1.c

/*
 * Copyright 1995-2019 The OpenSSL Project Authors. All Rights Reserved.
 *
 * Licensed under the Apache License 2.0 (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, mask;
    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 || num < 11) {
        RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,
               RSA_R_PKCS_DECODING_ERROR);
        return -1;
    }

    em = OPENSSL_malloc(num);
    if (em == NULL) {
        RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, ERR_R_MALLOC_FAILURE);
        return -1;
    }
    /*
     * Caller is encouraged to pass zero-padded message created with
     * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
     * bounds, it's impossible to have an invariant memory access pattern
     * in case |from| was not zero-padded in advance.
     */
    for (from += flen, em += num, i = 0; i < num; i++) {
        mask = ~constant_time_is_zero(flen);
        flen -= 1 & mask;
        from -= 1 & mask;
        *--em = *from & mask;
    }

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

    /* scan over padding data */
    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(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.
     */
    good &= constant_time_ge(tlen, mlen);

    /*
     * Even though we can't fake result's length, we can pretend copying
     * |tlen| bytes where |mlen| bytes would be real. Last |tlen| of |num|
     * bytes are viewed as circular buffer with start at |tlen|-|mlen'|,
     * where |mlen'| is "saturated" |mlen| value. Deducing information
     * about failure or |mlen| would take attacker's ability to observe
     * memory access pattern with byte granularity *as it occurs*. It
     * should be noted that failure is indistinguishable from normal
     * operation if |tlen| is fixed by protocol.
     */
    tlen = constant_time_select_int(constant_time_lt(num - 11, tlen),
                                    num - 11, tlen);
    msg_index = constant_time_select_int(good, msg_index, num - tlen);
    mlen = num - msg_index;
    for (mask = good, i = 0; i < tlen; i++) {
        unsigned int equals = constant_time_eq(msg_index, num);

        msg_index -= tlen & equals;  /* rewind at EOF */
        mask &= ~equals;  /* mask = 0 at EOF */
        to[i] = constant_time_select_8(mask, em[msg_index++], to[i]);
    }

    OPENSSL_clear_free(em, num);
    RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, RSA_R_PKCS_DECODING_ERROR);
    err_clear_last_constant_time(1 & good);

    return constant_time_select_int(good, mlen, -1);
}