From: "Arno Wagner" <arno@xxxxxxxxxxx>
Date: 06/10/16 12:04
Hi,
> the block size is always 512 bytes for cryptsetup. The
> tweak is, I think, the block-number as counted from the
> offset.
>
> You can read the key and offset as described in FAQ Item 6.10.
I've looked at sections 6.10/11/12 but could not come up with a clear definition. crypsetup loopaes.c has:
int LOOPAES_parse_keyfile(struct crypt_device *cd,
struct volume_key **vk,
const char *hash,
unsigned int *keys_count,
char *buffer,
size_t buffer_len)
{
[ ... ]
return hash_keys(cd, vk, hash, keys, key_index,
crypt_get_volume_key_size(cd), key_len);
}
hash_keys(...) has:
hash_name = hash_override ?: get_hash(key_len_output);
tweak = get_tweak(keys_count);
While get_tweaks(keys_count) is:
static unsigned char get_tweak(unsigned int keys_count)
{
switch (keys_count) {
case 64: return 0x55;
case 65: return 0xF4;
default: break;
}
return 0x00;
}
It seems that the tweak value can only be either 0x66 or 0xF4, or 0 ... does that makes sense ?
Thanks.
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