| /* |
| * 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); |
| } |