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Allow buggy behaviour in cbc functions

This commit is contained in:
ergo720 2018-12-18 18:46:12 +01:00
parent ef385087a8
commit 25d6fbc902
1 changed files with 29 additions and 22 deletions
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51
src/common/crypto/EmuDes.cpp
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@ -41,13 +41,13 @@
// in reverse order during a decryption operation. This is necessary because XcKeyTable doesn't provide an "operation" argument, that is, it
// always generates an encryption key schedule.
// NOTE: this des implementation doesn't produce exactly the same chipertext produced by the Xbox. I found that the implementation of Eric Young
// NOTE: this des implementation doesn't produce exactly the same ciphertext produced by the Xbox. I found that the implementation of Eric Young
// used in OpenSSL does instead, but we can't use it since it's under the Apache 2.0 license, which is incompatible with GPLv2. For reference,
// the DES-YOUN.zip package at https://www.schneier.com/books/applied_cryptography/source.html contains a previous version of the same code under
// the GPLv2 but again it doesn't produce the same chipertext, and modifying it to make it so would make it identical to the OpenSSL code, which
// is probably a violation of the license, so I won't do it. In practice, as long as the code correctly decrypts the chipertext (which it does),
// I don't think that the Xbox games will care if the chipertext is not exactly the same as on the Xbox and should work fine offline. The only
// problem with this is that cxbxr will be unable to comunicate with a real Xbox on the network (des is used in console-to-console comunications)
// the GPLv2 but again it doesn't produce the same ciphertext, and modifying it to make it so would make it identical to the OpenSSL code, which
// is probably a violation of the license, so I won't do it. In practice, as long as the code correctly decrypts the ciphertext (which it does),
// I don't think that the Xbox games will care if the ciphertext is not exactly the same as on the Xbox and should work fine offline. The only
// problem with this is that cxbxr will be unable to communicate with a real Xbox on the network (des is used in console-to-console communications)
// because the des key schedule generated on the console will be different and so it will fail to decrypt packets encrypted by cxbxr.
@ -450,19 +450,23 @@ int mbedtls_des_crypt_cbc(mbedtls_des_context* ctx,
const unsigned char* input,
unsigned char* output)
{
int i;
int i, ret, num_des_blocks;
unsigned char temp[8];
// I'm undecided regarding this check. The original code of ReactOS correctly checks that the input lenght is a multiple of a
// des_block (8 bytes) but the kernel doesn't and will encrypt up to block (lenght + 7) / 8. However, if we do that, we'll run
// the risk of reading some random bytes after the buffer end and/or touching invalid memory and crash.
ret = 0;
num_des_blocks = (length + 7) / 8;
// The original code of ReactOS correctly checks that the input lenght is a multiple of a des_block (8 bytes) but the
// kernel doesn't and will encrypt up to block (lenght + 7) / 8. This means that we'll run the risk of reading some
// random bytes after the buffer end and/or touching invalid memory and crash. Because the real kernel does it, we'll
// allow this buggy behaviour for the sake of accuracy.
if (length % 8) {
return MBEDTLS_ERR_DES_INVALID_INPUT_LENGTH;
ret = MBEDTLS_ERR_DES_INVALID_INPUT_LENGTH;
}
if (mode == MBEDTLS_DES_ENCRYPT)
{
while (length > 0)
while (num_des_blocks > 0)
{
for (i = 0; i < 8; i++) {
output[i] = (unsigned char)(input[i] ^ iv[i]);
@ -473,12 +477,12 @@ int mbedtls_des_crypt_cbc(mbedtls_des_context* ctx,
input += 8;
output += 8;
length -= 8;
num_des_blocks--;
}
}
else /* MBEDTLS_DES_DECRYPT */
{
while (length > 0)
while (num_des_blocks > 0)
{
memcpy(temp, input, 8);
mbedtls_des_crypt_ecb(ctx, input, output, MBEDTLS_DES_DECRYPT);
@ -491,11 +495,11 @@ int mbedtls_des_crypt_cbc(mbedtls_des_context* ctx,
input += 8;
output += 8;
length -= 8;
num_des_blocks--;
}
}
return 0;
return ret;
}
/*
@ -614,16 +618,19 @@ int mbedtls_des3_crypt_cbc(mbedtls_des3_context* ctx,
const unsigned char *input,
unsigned char *output)
{
int i;
int i, ret, num_des_blocks;
unsigned char temp[8];
ret = 0;
num_des_blocks = (length + 7) / 8;
if (length % 8) {
return MBEDTLS_ERR_DES_INVALID_INPUT_LENGTH;
ret = MBEDTLS_ERR_DES_INVALID_INPUT_LENGTH;
}
if (mode == MBEDTLS_DES_ENCRYPT)
{
while (length > 0)
while (num_des_blocks > 0)
{
for (i = 0; i < 8; i++) {
output[i] = (unsigned char)(input[i] ^ iv[i]);
@ -634,12 +641,12 @@ int mbedtls_des3_crypt_cbc(mbedtls_des3_context* ctx,
input += 8;
output += 8;
length -= 8;
num_des_blocks--;
}
}
else /* MBEDTLS_DES_DECRYPT */
{
while (length > 0)
while (num_des_blocks > 0)
{
memcpy(temp, input, 8);
mbedtls_des3_decrypt_ecb(ctx, input, output);
@ -652,9 +659,9 @@ int mbedtls_des3_crypt_cbc(mbedtls_des3_context* ctx,
input += 8;
output += 8;
length -= 8;
num_des_blocks--;
}
}
return 0;
return ret;
}