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Improve BNSF key detection

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bnnm 2020-02-22 20:41:17 +01:00
parent ca6d780d0e
commit 1290cea8ff
1 changed files with 27 additions and 7 deletions
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34
src/coding/g7221_decoder_lib.c
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@ -941,7 +941,7 @@ static int decode_vector_quantized_mlt_indices(uint32_t* data_u32, int* p_bitpos
}
/* unpacks input buffer into MLT coefs */
static int unpack_frame(int bit_rate, const uint8_t* data, int frame_size, /*int* p_frame_size, */ int* p_mag_shift, int16_t* mlt_coefs, uint32_t* p_random_value) {
static int unpack_frame(int bit_rate, const uint8_t* data, int frame_size, /*int* p_frame_size, */ int* p_mag_shift, int16_t* mlt_coefs, uint32_t* p_random_value, int test_errors) {
uint32_t data_u32[0x78/4 + 2];
int bitpos, expected_frame_size;
int power_categories[NUMBER_OF_REGIONS];
@ -1071,19 +1071,38 @@ static int unpack_frame(int bit_rate, const uint8_t* data, int frame_size, /*int
/* test for errors (in refdec but not Namco's, useful to detect decryption) */
{
if (test_errors) {
int bits_left = 8 * expected_frame_size - bitpos;
int i;
int i, endpos, test_bits;
if (bits_left > 0) {
/* frame must be padded with 1s */
endpos = bitpos;
for (i = 0; i < bits_left; i++) {
int bit = (data_u32[bitpos >> 5] >> (31 - (bitpos & 0x1F))) & 1;
bitpos++;
int bit = (data_u32[endpos >> 5] >> (31 - (endpos & 0x1F))) & 1;
endpos++;
if (bit == 0)
return -1;
}
/* extra: test we aren't in the middle of padding (happens with bad keys) */
endpos = bitpos;
test_bits = 8 * 0x04;
if (test_bits > bitpos)
test_bits = bitpos;
for (i = 0; i < test_bits; i++) {
int bit = (data_u32[endpos >> 5] >> (31 - (endpos & 0x1F))) & 1;
endpos--;
if (bit != 1)
break;
}
/* so many 1s isn't very normal */
if (i == test_bits)
return -8;
}
else {
/* ? */
@ -1145,10 +1164,11 @@ fail:
int g7221_decode_frame(g7221_handle* handle, uint8_t* data, int16_t* out_samples) {
int res;
int mag_shift;
int encrypted = handle->aes != NULL;
/* first 0x10 bytes may be encrypted with AES. Original code also saves encrypted bytes,
* then re-crypts after unpacking, presumably to guard against memdumps. */
if (handle->aes != NULL) {
if (encrypted) {
s14aes_decrypt(handle->aes, data);
}
@ -1156,7 +1176,7 @@ int g7221_decode_frame(g7221_handle* handle, uint8_t* data, int16_t* out_samples
* so we could avoid one extra buffer, but for clarity we'll leave as is */
/* unpack data into MLT spectrum coefs */
res = unpack_frame(handle->bit_rate, data, handle->frame_size, &mag_shift, handle->mlt_coefs, &handle->random_value);
res = unpack_frame(handle->bit_rate, data, handle->frame_size, &mag_shift, handle->mlt_coefs, &handle->random_value, encrypted);
if (res < 0) goto fail;
/* convert coefs to samples using reverse (inverse) MLT */