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/*
* Copyright 1995-2021 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.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 - RSA_PKCS1_PADDING_SIZE)) {
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 (tlen <= 0 || flen <= 0)
return -1;
if (flen > num || num < RSA_PKCS1_PADDING_SIZE) {
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;
}
good = constant_time_is_zero(em[0]);
good &= constant_time_eq(em[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(em[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(em[i], 3);
}
/*
* 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);
err = constant_time_select_int(mask | good, err,
RSA_R_NULL_BEFORE_BLOCK_MISSING);
mask = ~good;
/*
* Reject if nul delimiter is preceded by 8 consecutive 0x03 bytes. Note
* that RFC5246 incorrectly states this the other way around, i.e. reject
* if it is not preceded by 8 consecutive 0x03 bytes. However this is
* corrected in subsequent errata for that RFC.
*/
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);
/*
* Move the result in-place by |num|-RSA_PKCS1_PADDING_SIZE-|mlen| bytes to the left.
* Then if |good| move |mlen| bytes from |em|+RSA_PKCS1_PADDING_SIZE to |to|.
* Otherwise leave |to| unchanged.
* Copy the memory back in a way that does not reveal the size of
* the data being copied via a timing side channel. This requires copying
* parts of the buffer multiple times based on the bits set in the real
* length. Clear bits do a non-copy with identical access pattern.
* The loop below has overall complexity of O(N*log(N)).
*/
tlen = constant_time_select_int(constant_time_lt(num - RSA_PKCS1_PADDING_SIZE, tlen),
num - RSA_PKCS1_PADDING_SIZE, tlen);
for (msg_index = 1; msg_index < num - RSA_PKCS1_PADDING_SIZE; msg_index <<= 1) {
mask = ~constant_time_eq(msg_index & (num - RSA_PKCS1_PADDING_SIZE - mlen), 0);
for (i = RSA_PKCS1_PADDING_SIZE; i < num - msg_index; i++)
em[i] = constant_time_select_8(mask, em[i + msg_index], em[i]);
}
for (i = 0; i < tlen; i++) {
mask = good & constant_time_lt(i, mlen);
to[i] = constant_time_select_8(mask, em[i + RSA_PKCS1_PADDING_SIZE], 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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