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/*
* Copyright 1995-2018 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/rand.h>
#include "internal/constant_time_locl.h"
int RSA_padding_add_SSLv23(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_SSLV23,
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 - 8 - 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++;
}
memset(p, 3, 8);
p += 8;
*(p++) = '\0';
memcpy(p, from, (unsigned int)flen);
return 1;
}
/*
* Copy of RSA_padding_check_PKCS1_type_2 with a twist that rejects padding
* if nul delimiter is preceded by 8 consecutive 0x03 bytes. It also
* preserves error code reporting for backward compatibility.
*/
int RSA_padding_check_SSLv23(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, threes_in_row;
int zero_index = 0, msg_index, mlen = -1, err;
if (flen < 10) {
RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_DATA_TOO_SMALL);
return -1;
}
em = OPENSSL_malloc(num);
if (em == NULL) {
RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, 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;
}
from = em;
good = constant_time_is_zero(from[0]);
good &= constant_time_eq(from[1], 2);
err = constant_time_select_int(good, 0, RSA_R_BLOCK_TYPE_IS_NOT_02);
mask = ~good;
/* scan over padding data */
found_zero_byte = 0;
threes_in_row = 0;
for (i = 2; i < num; i++) {
unsigned int equals0 = constant_time_is_zero(from[i]);
zero_index = constant_time_select_int(~found_zero_byte & equals0,
i, zero_index);
found_zero_byte |= equals0;
threes_in_row += 1 & ~found_zero_byte;
threes_in_row &= found_zero_byte | constant_time_eq(from[i], 3);
}
/*
* PS must be at least 8 bytes long, and it starts two bytes into |from|.
* 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);
err = constant_time_select_int(mask | good, err,
RSA_R_NULL_BEFORE_BLOCK_MISSING);
mask = ~good;
good &= constant_time_lt(threes_in_row, 8);
err = constant_time_select_int(mask | good, err,
RSA_R_SSLV3_ROLLBACK_ATTACK);
mask = ~good;
/*
* 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);
err = constant_time_select_int(mask | good, err, RSA_R_DATA_TOO_LARGE);
/*
* 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, tlen), num, tlen);
msg_index = constant_time_select_int(good, msg_index, num - tlen);
mlen = num - msg_index;
for (from += msg_index, mask = good, i = 0; i < tlen; i++) {
unsigned int equals = constant_time_eq(i, mlen);
from -= tlen & equals; /* if (i == mlen) rewind */
mask &= mask ^ equals; /* if (i == mlen) mask = 0 */
to[i] = constant_time_select_8(mask, from[i], to[i]);
}
OPENSSL_clear_free(em, num);
RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, err);
err_clear_last_constant_time(1 & good);
return constant_time_select_int(good, mlen, -1);
}
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