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fixes #1239: remove AES padding attack for 7zip since we can't guarantee that the padding is always zero

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This commit is contained in:
philsmd 2017-05-17 13:53:55 +02:00
parent 7bd391df71
commit 1f93d2060f
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GPG Key ID: 4F25D016D9D6A8AF
2 changed files with 2 additions and 189 deletions
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5
include/interface.h
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@ -808,11 +808,6 @@ typedef struct seven_zip_hook_salt
char coder_attributes[5 + 1];
u8 coder_attributes_len;
u32 margin;
bool padding_check_full;
bool padding_check_fast;
int aes_len; // pre-computed length of the maximal (subset of) data we need for AES-CBC
} seven_zip_hook_salt_t;

186
src/interface.c
View File

@ -11854,21 +11854,6 @@ int seven_zip_parse_hash (u8 *input_buf, u32 input_len, hash_t *hash_buf, MAYBE_
seven_zip->aes_len = aes_len;
const u32 margin = data_len - unpack_size;
seven_zip->margin = margin;
seven_zip->padding_check_fast = (margin > 0) && (data_len >= 32);
if ((margin > 0) && (data_len < 32))
{
if ((data_len - aes_len) <= 16) // we need the same amount of AES BLOCKS (should always be true)!
{
seven_zip->padding_check_full = true; // determine if AES-CBC padding attack is possible
}
}
else
{
seven_zip->padding_check_full = false;
}
if (data_type != 0x80)
{
@ -14798,14 +14783,7 @@ void seven_zip_hook_func (hc_device_param_t *device_param, hashes_t *hashes, con
u8 data_type = seven_zip->data_type;
u32 *data_buf = seven_zip->data_buf;
u32 data_len = seven_zip->data_len;
u32 unpack_size = seven_zip->unpack_size;
u32 margin = seven_zip->margin;
// can we use the padding attack:
u32 padding_check_fast = seven_zip->padding_check_fast;
u32 padding_check_full = seven_zip->padding_check_full;
for (u32 pw_pos = 0; pw_pos < pws_cnt; pw_pos++)
{
@ -14823,99 +14801,6 @@ void seven_zip_hook_func (hc_device_param_t *device_param, hashes_t *hashes, con
AES_set_decrypt_key (ukey, 256, &aes_key);
AES_KEY aes_key_copied;
memcpy (&aes_key_copied, &aes_key, sizeof (AES_KEY));
if (padding_check_fast == true) // use part of the data as initialization vector
{
u8 *data_buf_ptr = (u8 *) data_buf;
u32 data_tmp_buf[8];
memcpy (&data_tmp_buf, data_buf_ptr + data_len - 32, 32);
u32 data[4];
data[0] = data_tmp_buf[4];
data[1] = data_tmp_buf[5];
data[2] = data_tmp_buf[6];
data[3] = data_tmp_buf[7];
u32 out[4];
AES_decrypt (&aes_key, (u8*) data, (u8*) out);
out[0] ^= data_tmp_buf[0];
out[1] ^= data_tmp_buf[1];
out[2] ^= data_tmp_buf[2];
out[3] ^= data_tmp_buf[3];
switch (margin)
{
case 15: out[0] &= 0xffffff00;
break;
case 14: out[0] &= 0xffff0000;
break;
case 13: out[0] &= 0xff000000;
break;
case 12: out[0] = 0;
break;
case 11: out[0] = 0;
out[1] &= 0xffffff00;
break;
case 10: out[0] = 0;
out[1] &= 0xffff0000;
break;
case 9: out[0] = 0;
out[1] &= 0xff000000;
break;
case 8: out[0] = 0;
out[1] = 0;
break;
case 7: out[0] = 0;
out[1] = 0;
out[2] &= 0xffffff00;
break;
case 6: out[0] = 0;
out[1] = 0;
out[2] &= 0xffff0000;
break;
case 5: out[0] = 0;
out[1] = 0;
out[2] &= 0xff000000;
break;
case 4: out[0] = 0;
out[1] = 0;
out[2] = 0;
break;
case 3: out[0] = 0;
out[1] = 0;
out[2] = 0;
out[3] &= 0xffffff00;
break;
case 2: out[0] = 0;
out[1] = 0;
out[2] = 0;
out[3] &= 0xffff0000;
break;
case 1: out[0] = 0;
out[1] = 0;
out[2] = 0;
out[3] &= 0xff000000;
break;
}
if ((out[0] != 0) || (out[1] != 0) || (out[2] != 0) || (out[3] != 0))
{
hook_item->hook_success = 0;
continue;
}
}
// if the previous check was okay, we need to do some more staff to eliminate some possible false positives
int aes_len = seven_zip->aes_len;
u32 data[4];
@ -14941,7 +14826,7 @@ void seven_zip_hook_func (hc_device_param_t *device_param, hashes_t *hashes, con
data[2] = data_buf[j + 2];
data[3] = data_buf[j + 3];
AES_decrypt (&aes_key_copied, (u8*) data, (u8*) out);
AES_decrypt (&aes_key, (u8*) data, (u8*) out);
out[0] ^= iv[0];
out[1] ^= iv[1];
@ -14966,7 +14851,7 @@ void seven_zip_hook_func (hc_device_param_t *device_param, hashes_t *hashes, con
data[2] = data_buf[j + 2];
data[3] = data_buf[j + 3];
AES_decrypt (&aes_key_copied, (u8*) data, (u8*) out);
AES_decrypt (&aes_key, (u8*) data, (u8*) out);
out[0] ^= iv[0];
out[1] ^= iv[1];
@ -14978,73 +14863,6 @@ void seven_zip_hook_func (hc_device_param_t *device_param, hashes_t *hashes, con
out_full[j + 2] = out[2];
out_full[j + 3] = out[3];
if (padding_check_full == true)
{
// do the check if margin > 0 but data_len < 32
switch (margin)
{
case 15: out[0] &= 0xffffff00;
break;
case 14: out[0] &= 0xffff0000;
break;
case 13: out[0] &= 0xff000000;
break;
case 12: out[0] = 0;
break;
case 11: out[0] = 0;
out[1] &= 0xffffff00;
break;
case 10: out[0] = 0;
out[1] &= 0xffff0000;
break;
case 9: out[0] = 0;
out[1] &= 0xff000000;
break;
case 8: out[0] = 0;
out[1] = 0;
break;
case 7: out[0] = 0;
out[1] = 0;
out[2] &= 0xffffff00;
break;
case 6: out[0] = 0;
out[1] = 0;
out[2] &= 0xffff0000;
break;
case 5: out[0] = 0;
out[1] = 0;
out[2] &= 0xff000000;
break;
case 4: out[0] = 0;
out[1] = 0;
out[2] = 0;
break;
case 3: out[0] = 0;
out[1] = 0;
out[2] = 0;
out[3] &= 0xffffff00;
break;
case 2: out[0] = 0;
out[1] = 0;
out[2] = 0;
out[3] &= 0xffff0000;
break;
case 1: out[0] = 0;
out[1] = 0;
out[2] = 0;
out[3] &= 0xff000000;
break;
}
if ((out[0] != 0) || (out[1] != 0) || (out[2] != 0) || (out[3] != 0))
{
hook_item->hook_success = 0;
continue;
}
}
if (data_type > 2)
{
// This decompression is currently not supported