On 12/08/2019 09:50, Ard Biesheuvel wrote: > On Mon, 12 Aug 2019 at 10:44, Milan Broz <gmazyland@xxxxxxxxx> wrote: >> >> On 12/08/2019 08:54, Ard Biesheuvel wrote: >>> On Mon, 12 Aug 2019 at 09:33, Milan Broz <gmazyland@xxxxxxxxx> wrote: >>>> Try for example >>>> # cryptsetup luksFormat /dev/sdc -c aes-cbc-essiv:sha256 --integrity hmac-sha256 -q -i1 >>>> >>>> It should produce Crypto API string >>>> authenc(hmac(sha256),essiv(cbc(aes),sha256)) >>>> while it produces >>>> essiv(authenc(hmac(sha256),cbc(aes)),sha256) >>>> (and fails). >>>> >>> >>> No. I don't know why it fails, but the latter is actually the correct >>> string. The essiv template is instantiated either as a skcipher or as >>> an aead, and it encapsulates the entire transformation. (This is >>> necessary considering that the IV is passed via the AAD and so the >>> ESSIV handling needs to touch that as well) >> >> Hm. Constructing these strings seems to be more confusing than dmcrypt mode combinations :-) >> >> But you are right, I actually tried the former string (authenc(hmac(sha256),essiv(cbc(aes),sha256))) >> and it worked, but I guess the authenticated IV (AAD) was actually the input to IV (plain sector number) >> not the output of ESSIV? Do I understand it correctly now? >> > > Indeed. The former string instantiates the skcipher version of the > ESSIV template, and so the AAD handling is omitted, and we end up > using the plain IV in the authentication rather than the encrypted IV. > > So when using the latter string, does it produce any error messages > when it fails? The error is table: 253:1: crypt: Error decoding and setting key and it is failing in crypt_setkey() int this crypto_aead_setkey(); And it is because it now wrongly calculates MAC key length. (We have two keys here - one for length-preserving CBC-ESSIV encryption and one for HMAC.) This super-ugly hotfix helps here... I guess it can be done better :-) diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c index e9a0093c88ee..7b06d975a2e1 100644 --- a/drivers/md/dm-crypt.c +++ b/drivers/md/dm-crypt.c @@ -2342,6 +2342,9 @@ static int crypt_ctr_auth_cipher(struct crypt_config *cc, char *cipher_api) char *start, *end, *mac_alg = NULL; struct crypto_ahash *mac; + if (strstarts(cipher_api, "essiv(authenc(")) + cipher_api += strlen("essiv("); + if (!strstarts(cipher_api, "authenc(")) return 0; Milan