647 lines
22 KiB
C
647 lines
22 KiB
C
/*
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* Copyright 1995-2023 The OpenSSL Project Authors. All Rights Reserved.
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*
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* Licensed under the Apache License 2.0 (the "License"). You may not use
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* this file except in compliance with the License. You can obtain a copy
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* in the file LICENSE in the source distribution or at
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* https://www.openssl.org/source/license.html
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*/
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/*
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* RSA low level APIs are deprecated for public use, but still ok for
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* internal use.
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*/
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#include "internal/deprecated.h"
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#include "internal/constant_time.h"
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#include <stdio.h>
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#include <openssl/bn.h>
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#include <openssl/rsa.h>
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#include <openssl/rand.h>
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/* Just for the SSL_MAX_MASTER_KEY_LENGTH value */
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#include <openssl/prov_ssl.h>
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#include <openssl/evp.h>
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#include <openssl/sha.h>
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#include <openssl/hmac.h>
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#include "internal/cryptlib.h"
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#include "crypto/rsa.h"
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#include "rsa_local.h"
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int RSA_padding_add_PKCS1_type_1(unsigned char *to, int tlen,
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const unsigned char *from, int flen)
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{
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int j;
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unsigned char *p;
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if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {
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ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
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return 0;
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}
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p = (unsigned char *)to;
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*(p++) = 0;
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*(p++) = 1; /* Private Key BT (Block Type) */
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/* pad out with 0xff data */
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j = tlen - 3 - flen;
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memset(p, 0xff, j);
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p += j;
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*(p++) = '\0';
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memcpy(p, from, (unsigned int)flen);
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return 1;
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}
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int RSA_padding_check_PKCS1_type_1(unsigned char *to, int tlen,
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const unsigned char *from, int flen,
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int num)
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{
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int i, j;
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const unsigned char *p;
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p = from;
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/*
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* The format is
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* 00 || 01 || PS || 00 || D
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* PS - padding string, at least 8 bytes of FF
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* D - data.
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*/
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if (num < RSA_PKCS1_PADDING_SIZE)
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return -1;
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/* Accept inputs with and without the leading 0-byte. */
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if (num == flen) {
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if ((*p++) != 0x00) {
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ERR_raise(ERR_LIB_RSA, RSA_R_INVALID_PADDING);
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return -1;
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}
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flen--;
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}
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if ((num != (flen + 1)) || (*(p++) != 0x01)) {
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ERR_raise(ERR_LIB_RSA, RSA_R_BLOCK_TYPE_IS_NOT_01);
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return -1;
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}
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/* scan over padding data */
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j = flen - 1; /* one for type. */
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for (i = 0; i < j; i++) {
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if (*p != 0xff) { /* should decrypt to 0xff */
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if (*p == 0) {
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p++;
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break;
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} else {
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ERR_raise(ERR_LIB_RSA, RSA_R_BAD_FIXED_HEADER_DECRYPT);
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return -1;
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}
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}
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p++;
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}
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if (i == j) {
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ERR_raise(ERR_LIB_RSA, RSA_R_NULL_BEFORE_BLOCK_MISSING);
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return -1;
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}
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if (i < 8) {
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ERR_raise(ERR_LIB_RSA, RSA_R_BAD_PAD_BYTE_COUNT);
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return -1;
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}
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i++; /* Skip over the '\0' */
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j -= i;
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if (j > tlen) {
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ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE);
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return -1;
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}
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memcpy(to, p, (unsigned int)j);
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return j;
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}
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int ossl_rsa_padding_add_PKCS1_type_2_ex(OSSL_LIB_CTX *libctx, unsigned char *to,
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int tlen, const unsigned char *from,
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int flen)
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{
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int i, j;
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unsigned char *p;
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if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {
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ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
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return 0;
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} else if (flen < 0) {
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ERR_raise(ERR_LIB_RSA, RSA_R_INVALID_LENGTH);
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return 0;
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}
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p = (unsigned char *)to;
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*(p++) = 0;
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*(p++) = 2; /* Public Key BT (Block Type) */
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/* pad out with non-zero random data */
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j = tlen - 3 - flen;
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if (RAND_bytes_ex(libctx, p, j, 0) <= 0)
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return 0;
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for (i = 0; i < j; i++) {
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if (*p == '\0')
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do {
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if (RAND_bytes_ex(libctx, p, 1, 0) <= 0)
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return 0;
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} while (*p == '\0');
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p++;
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}
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*(p++) = '\0';
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memcpy(p, from, (unsigned int)flen);
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return 1;
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}
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int RSA_padding_add_PKCS1_type_2(unsigned char *to, int tlen,
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const unsigned char *from, int flen)
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{
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return ossl_rsa_padding_add_PKCS1_type_2_ex(NULL, to, tlen, from, flen);
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}
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int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen,
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const unsigned char *from, int flen,
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int num)
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{
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int i;
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/* |em| is the encoded message, zero-padded to exactly |num| bytes */
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unsigned char *em = NULL;
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unsigned int good, found_zero_byte, mask;
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int zero_index = 0, msg_index, mlen = -1;
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if (tlen <= 0 || flen <= 0)
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return -1;
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/*
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* PKCS#1 v1.5 decryption. See "PKCS #1 v2.2: RSA Cryptography Standard",
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* section 7.2.2.
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*/
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if (flen > num || num < RSA_PKCS1_PADDING_SIZE) {
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ERR_raise(ERR_LIB_RSA, RSA_R_PKCS_DECODING_ERROR);
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return -1;
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}
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em = OPENSSL_malloc(num);
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if (em == NULL)
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return -1;
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/*
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* Caller is encouraged to pass zero-padded message created with
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* BN_bn2binpad. Trouble is that since we can't read out of |from|'s
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* bounds, it's impossible to have an invariant memory access pattern
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* in case |from| was not zero-padded in advance.
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*/
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for (from += flen, em += num, i = 0; i < num; i++) {
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mask = ~constant_time_is_zero(flen);
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flen -= 1 & mask;
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from -= 1 & mask;
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*--em = *from & mask;
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}
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good = constant_time_is_zero(em[0]);
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good &= constant_time_eq(em[1], 2);
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/* scan over padding data */
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found_zero_byte = 0;
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for (i = 2; i < num; i++) {
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unsigned int equals0 = constant_time_is_zero(em[i]);
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zero_index = constant_time_select_int(~found_zero_byte & equals0,
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i, zero_index);
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found_zero_byte |= equals0;
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}
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/*
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* PS must be at least 8 bytes long, and it starts two bytes into |em|.
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* If we never found a 0-byte, then |zero_index| is 0 and the check
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* also fails.
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*/
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good &= constant_time_ge(zero_index, 2 + 8);
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/*
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* Skip the zero byte. This is incorrect if we never found a zero-byte
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* but in this case we also do not copy the message out.
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*/
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msg_index = zero_index + 1;
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mlen = num - msg_index;
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/*
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* For good measure, do this check in constant time as well.
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*/
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good &= constant_time_ge(tlen, mlen);
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/*
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* Move the result in-place by |num|-RSA_PKCS1_PADDING_SIZE-|mlen| bytes to the left.
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* Then if |good| move |mlen| bytes from |em|+RSA_PKCS1_PADDING_SIZE to |to|.
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* Otherwise leave |to| unchanged.
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* Copy the memory back in a way that does not reveal the size of
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* the data being copied via a timing side channel. This requires copying
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* parts of the buffer multiple times based on the bits set in the real
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* length. Clear bits do a non-copy with identical access pattern.
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* The loop below has overall complexity of O(N*log(N)).
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*/
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tlen = constant_time_select_int(constant_time_lt(num - RSA_PKCS1_PADDING_SIZE, tlen),
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num - RSA_PKCS1_PADDING_SIZE, tlen);
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for (msg_index = 1; msg_index < num - RSA_PKCS1_PADDING_SIZE; msg_index <<= 1) {
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mask = ~constant_time_eq(msg_index & (num - RSA_PKCS1_PADDING_SIZE - mlen), 0);
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for (i = RSA_PKCS1_PADDING_SIZE; i < num - msg_index; i++)
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em[i] = constant_time_select_8(mask, em[i + msg_index], em[i]);
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}
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for (i = 0; i < tlen; i++) {
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mask = good & constant_time_lt(i, mlen);
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to[i] = constant_time_select_8(mask, em[i + RSA_PKCS1_PADDING_SIZE], to[i]);
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}
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OPENSSL_clear_free(em, num);
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#ifndef FIPS_MODULE
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/*
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* This trick doesn't work in the FIPS provider because libcrypto manages
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* the error stack. Instead we opt not to put an error on the stack at all
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* in case of padding failure in the FIPS provider.
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*/
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ERR_raise(ERR_LIB_RSA, RSA_R_PKCS_DECODING_ERROR);
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err_clear_last_constant_time(1 & good);
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#endif
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return constant_time_select_int(good, mlen, -1);
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}
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static int ossl_rsa_prf(OSSL_LIB_CTX *ctx,
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unsigned char *to, int tlen,
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const char *label, int llen,
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const unsigned char *kdk,
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uint16_t bitlen)
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{
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int pos;
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int ret = -1;
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uint16_t iter = 0;
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unsigned char be_iter[sizeof(iter)];
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unsigned char be_bitlen[sizeof(bitlen)];
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HMAC_CTX *hmac = NULL;
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EVP_MD *md = NULL;
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unsigned char hmac_out[SHA256_DIGEST_LENGTH];
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unsigned int md_len;
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if (tlen * 8 != bitlen) {
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ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);
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return ret;
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}
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be_bitlen[0] = (bitlen >> 8) & 0xff;
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be_bitlen[1] = bitlen & 0xff;
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hmac = HMAC_CTX_new();
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if (hmac == NULL) {
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ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);
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goto err;
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}
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/*
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* we use hardcoded hash so that migrating between versions that use
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* different hash doesn't provide a Bleichenbacher oracle:
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* if the attacker can see that different versions return different
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* messages for the same ciphertext, they'll know that the message is
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* synthetically generated, which means that the padding check failed
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*/
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md = EVP_MD_fetch(ctx, "sha256", NULL);
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if (md == NULL) {
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ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);
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goto err;
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}
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if (HMAC_Init_ex(hmac, kdk, SHA256_DIGEST_LENGTH, md, NULL) <= 0) {
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ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);
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goto err;
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}
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for (pos = 0; pos < tlen; pos += SHA256_DIGEST_LENGTH, iter++) {
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if (HMAC_Init_ex(hmac, NULL, 0, NULL, NULL) <= 0) {
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ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);
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goto err;
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}
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be_iter[0] = (iter >> 8) & 0xff;
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be_iter[1] = iter & 0xff;
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if (HMAC_Update(hmac, be_iter, sizeof(be_iter)) <= 0) {
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ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);
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goto err;
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}
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if (HMAC_Update(hmac, (unsigned char *)label, llen) <= 0) {
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ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);
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goto err;
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}
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if (HMAC_Update(hmac, be_bitlen, sizeof(be_bitlen)) <= 0) {
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ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);
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goto err;
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}
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/*
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* HMAC_Final requires the output buffer to fit the whole MAC
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* value, so we need to use the intermediate buffer for the last
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* unaligned block
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*/
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md_len = SHA256_DIGEST_LENGTH;
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if (pos + SHA256_DIGEST_LENGTH > tlen) {
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if (HMAC_Final(hmac, hmac_out, &md_len) <= 0) {
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ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);
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goto err;
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}
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memcpy(to + pos, hmac_out, tlen - pos);
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} else {
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if (HMAC_Final(hmac, to + pos, &md_len) <= 0) {
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ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);
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goto err;
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}
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}
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}
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ret = 0;
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err:
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HMAC_CTX_free(hmac);
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EVP_MD_free(md);
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return ret;
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}
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/*
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* ossl_rsa_padding_check_PKCS1_type_2() checks and removes the PKCS#1 type 2
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* padding from a decrypted RSA message. Unlike the
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* RSA_padding_check_PKCS1_type_2() it will not return an error in case it
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* detects a padding error, rather it will return a deterministically generated
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* random message. In other words it will perform an implicit rejection
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* of an invalid padding. This means that the returned value does not indicate
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* if the padding of the encrypted message was correct or not, making
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* side channel attacks like the ones described by Bleichenbacher impossible
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* without access to the full decrypted value and a brute-force search of
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* remaining padding bytes
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*/
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int ossl_rsa_padding_check_PKCS1_type_2(OSSL_LIB_CTX *ctx,
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unsigned char *to, int tlen,
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const unsigned char *from, int flen,
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int num, unsigned char *kdk)
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{
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/*
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* We need to generate a random length for the synthetic message, to avoid
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* bias towards zero and avoid non-constant timeness of DIV, we prepare
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* 128 values to check if they are not too large for the used key size,
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* and use 0 in case none of them are small enough, as 2^-128 is a good enough
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* safety margin
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*/
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#define MAX_LEN_GEN_TRIES 128
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unsigned char *synthetic = NULL;
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int synthetic_length;
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uint16_t len_candidate;
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unsigned char candidate_lengths[MAX_LEN_GEN_TRIES * sizeof(len_candidate)];
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uint16_t len_mask;
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uint16_t max_sep_offset;
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int synth_msg_index = 0;
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int ret = -1;
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int i, j;
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unsigned int good, found_zero_byte;
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int zero_index = 0, msg_index;
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/*
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* If these checks fail then either the message in publicly invalid, or
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* we've been called incorrectly. We can fail immediately.
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* Since this code is called only internally by openssl, those are just
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* sanity checks
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*/
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if (num != flen || tlen <= 0 || flen <= 0) {
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ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);
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return -1;
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}
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/* Generate a random message to return in case the padding checks fail */
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synthetic = OPENSSL_malloc(flen);
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if (synthetic == NULL) {
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ERR_raise(ERR_LIB_RSA, ERR_R_MALLOC_FAILURE);
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return -1;
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}
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if (ossl_rsa_prf(ctx, synthetic, flen, "message", 7, kdk, flen * 8) < 0)
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goto err;
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/* decide how long the random message should be */
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if (ossl_rsa_prf(ctx, candidate_lengths, sizeof(candidate_lengths),
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"length", 6, kdk,
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MAX_LEN_GEN_TRIES * sizeof(len_candidate) * 8) < 0)
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goto err;
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/*
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* max message size is the size of the modulus size less 2 bytes for
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* version and padding type and a minimum of 8 bytes padding
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*/
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len_mask = max_sep_offset = flen - 2 - 8;
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/*
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* we want a mask so lets propagate the high bit to all positions less
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* significant than it
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*/
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len_mask |= len_mask >> 1;
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len_mask |= len_mask >> 2;
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len_mask |= len_mask >> 4;
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len_mask |= len_mask >> 8;
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synthetic_length = 0;
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for (i = 0; i < MAX_LEN_GEN_TRIES * (int)sizeof(len_candidate);
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i += sizeof(len_candidate)) {
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len_candidate = (candidate_lengths[i] << 8) | candidate_lengths[i + 1];
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len_candidate &= len_mask;
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synthetic_length = constant_time_select_int(
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constant_time_lt(len_candidate, max_sep_offset),
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len_candidate, synthetic_length);
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}
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synth_msg_index = flen - synthetic_length;
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/* we have alternative message ready, check the real one */
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good = constant_time_is_zero(from[0]);
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good &= constant_time_eq(from[1], 2);
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/* then look for the padding|message separator (the first zero byte) */
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found_zero_byte = 0;
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for (i = 2; i < flen; i++) {
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unsigned int equals0 = constant_time_is_zero(from[i]);
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zero_index = constant_time_select_int(~found_zero_byte & equals0,
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i, zero_index);
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found_zero_byte |= equals0;
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}
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/*
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* padding must be at least 8 bytes long, and it starts two bytes into
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* |from|. If we never found a 0-byte, then |zero_index| is 0 and the check
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* also fails.
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*/
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good &= constant_time_ge(zero_index, 2 + 8);
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/*
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* Skip the zero byte. This is incorrect if we never found a zero-byte
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* but in this case we also do not copy the message out.
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*/
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msg_index = zero_index + 1;
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/*
|
|
* old code returned an error in case the decrypted message wouldn't fit
|
|
* into the |to|, since that would leak information, return the synthetic
|
|
* message instead
|
|
*/
|
|
good &= constant_time_ge(tlen, num - msg_index);
|
|
|
|
msg_index = constant_time_select_int(good, msg_index, synth_msg_index);
|
|
|
|
/*
|
|
* since at this point the |msg_index| does not provide the signal
|
|
* indicating if the padding check failed or not, we don't have to worry
|
|
* about leaking the length of returned message, we still need to ensure
|
|
* that we read contents of both buffers so that cache accesses don't leak
|
|
* the value of |good|
|
|
*/
|
|
for (i = msg_index, j = 0; i < flen && j < tlen; i++, j++)
|
|
to[j] = constant_time_select_8(good, from[i], synthetic[i]);
|
|
ret = j;
|
|
|
|
err:
|
|
/*
|
|
* the only time ret < 0 is when the ciphertext is publicly invalid
|
|
* or we were called with invalid parameters, so we don't have to perform
|
|
* a side-channel secure raising of the error
|
|
*/
|
|
if (ret < 0)
|
|
ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);
|
|
OPENSSL_free(synthetic);
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* ossl_rsa_padding_check_PKCS1_type_2_TLS() checks and removes the PKCS1 type 2
|
|
* padding from a decrypted RSA message in a TLS signature. The result is stored
|
|
* in the buffer pointed to by |to| which should be |tlen| bytes long. |tlen|
|
|
* must be at least SSL_MAX_MASTER_KEY_LENGTH. The original decrypted message
|
|
* should be stored in |from| which must be |flen| bytes in length and padded
|
|
* such that |flen == RSA_size()|. The TLS protocol version that the client
|
|
* originally requested should be passed in |client_version|. Some buggy clients
|
|
* can exist which use the negotiated version instead of the originally
|
|
* requested protocol version. If it is necessary to work around this bug then
|
|
* the negotiated protocol version can be passed in |alt_version|, otherwise 0
|
|
* should be passed.
|
|
*
|
|
* If the passed message is publicly invalid or some other error that can be
|
|
* treated in non-constant time occurs then -1 is returned. On success the
|
|
* length of the decrypted data is returned. This will always be
|
|
* SSL_MAX_MASTER_KEY_LENGTH. If an error occurs that should be treated in
|
|
* constant time then this function will appear to return successfully, but the
|
|
* decrypted data will be randomly generated (as per
|
|
* https://tools.ietf.org/html/rfc5246#section-7.4.7.1).
|
|
*/
|
|
int ossl_rsa_padding_check_PKCS1_type_2_TLS(OSSL_LIB_CTX *libctx,
|
|
unsigned char *to, size_t tlen,
|
|
const unsigned char *from,
|
|
size_t flen, int client_version,
|
|
int alt_version)
|
|
{
|
|
unsigned int i, good, version_good;
|
|
unsigned char rand_premaster_secret[SSL_MAX_MASTER_KEY_LENGTH];
|
|
|
|
/*
|
|
* If these checks fail then either the message in publicly invalid, or
|
|
* we've been called incorrectly. We can fail immediately.
|
|
*/
|
|
if (flen < RSA_PKCS1_PADDING_SIZE + SSL_MAX_MASTER_KEY_LENGTH
|
|
|| tlen < SSL_MAX_MASTER_KEY_LENGTH) {
|
|
ERR_raise(ERR_LIB_RSA, RSA_R_PKCS_DECODING_ERROR);
|
|
return -1;
|
|
}
|
|
|
|
/*
|
|
* Generate a random premaster secret to use in the event that we fail
|
|
* to decrypt.
|
|
*/
|
|
if (RAND_priv_bytes_ex(libctx, rand_premaster_secret,
|
|
sizeof(rand_premaster_secret), 0) <= 0) {
|
|
ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);
|
|
return -1;
|
|
}
|
|
|
|
good = constant_time_is_zero(from[0]);
|
|
good &= constant_time_eq(from[1], 2);
|
|
|
|
/* Check we have the expected padding data */
|
|
for (i = 2; i < flen - SSL_MAX_MASTER_KEY_LENGTH - 1; i++)
|
|
good &= ~constant_time_is_zero_8(from[i]);
|
|
good &= constant_time_is_zero_8(from[flen - SSL_MAX_MASTER_KEY_LENGTH - 1]);
|
|
|
|
|
|
/*
|
|
* If the version in the decrypted pre-master secret is correct then
|
|
* version_good will be 0xff, otherwise it'll be zero. The
|
|
* Klima-Pokorny-Rosa extension of Bleichenbacher's attack
|
|
* (http://eprint.iacr.org/2003/052/) exploits the version number
|
|
* check as a "bad version oracle". Thus version checks are done in
|
|
* constant time and are treated like any other decryption error.
|
|
*/
|
|
version_good =
|
|
constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH],
|
|
(client_version >> 8) & 0xff);
|
|
version_good &=
|
|
constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH + 1],
|
|
client_version & 0xff);
|
|
|
|
/*
|
|
* The premaster secret must contain the same version number as the
|
|
* ClientHello to detect version rollback attacks (strangely, the
|
|
* protocol does not offer such protection for DH ciphersuites).
|
|
* However, buggy clients exist that send the negotiated protocol
|
|
* version instead if the server does not support the requested
|
|
* protocol version. If SSL_OP_TLS_ROLLBACK_BUG is set then we tolerate
|
|
* such clients. In that case alt_version will be non-zero and set to
|
|
* the negotiated version.
|
|
*/
|
|
if (alt_version > 0) {
|
|
unsigned int workaround_good;
|
|
|
|
workaround_good =
|
|
constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH],
|
|
(alt_version >> 8) & 0xff);
|
|
workaround_good &=
|
|
constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH + 1],
|
|
alt_version & 0xff);
|
|
version_good |= workaround_good;
|
|
}
|
|
|
|
good &= version_good;
|
|
|
|
|
|
/*
|
|
* Now copy the result over to the to buffer if good, or random data if
|
|
* not good.
|
|
*/
|
|
for (i = 0; i < SSL_MAX_MASTER_KEY_LENGTH; i++) {
|
|
to[i] =
|
|
constant_time_select_8(good,
|
|
from[flen - SSL_MAX_MASTER_KEY_LENGTH + i],
|
|
rand_premaster_secret[i]);
|
|
}
|
|
|
|
/*
|
|
* We must not leak whether a decryption failure occurs because of
|
|
* Bleichenbacher's attack on PKCS #1 v1.5 RSA padding (see RFC 2246,
|
|
* section 7.4.7.1). The code follows that advice of the TLS RFC and
|
|
* generates a random premaster secret for the case that the decrypt
|
|
* fails. See https://tools.ietf.org/html/rfc5246#section-7.4.7.1
|
|
* So, whether we actually succeeded or not, return success.
|
|
*/
|
|
|
|
return SSL_MAX_MASTER_KEY_LENGTH;
|
|
}
|