On 3/9/2015 5:08 PM, Martin Hicks wrote: > On Mon, Mar 9, 2015 at 6:16 AM, Horia Geantă <horia.geanta@xxxxxxxxxxxxx> wrote: >> On 3/3/2015 7:44 PM, Martin Hicks wrote: >>> On Tue, Mar 3, 2015 at 10:44 AM, Horia Geantă >>> <horia.geanta@xxxxxxxxxxxxx> wrote: >>>> >>>> For talitos, there are two cases: >>>> >>>> 1. request data size is <= data unit / sector size >>>> talitos can handle any IV / tweak scheme >>>> >>>> 2. request data size > sector size >>>> since talitos internally generates the IV for the next sector by >>>> incrementing the previous IV, only IV schemes that allocate consecutive >>>> IV to consecutive sectors will function correctly. >>>> >>> >>> it's not clear to me that #1 is right. I guess it could be, but the >>> IV length would be limited to 8 bytes. >> >> Yes, there's a limitation in talitos wrt. XTS IV / tweak size - it's up >> to 8 bytes. >> So I guess ESSIV won't work with talitos-xts, since the encrypted IV >> output is 16 bytes. >> But as previously said, ESSIV breaks the XTS standard requirement for >> having a consecutive IV for consecutive blocks. ESSIV should really be >> used only with disk-level encryption schemes that require an >> unpredictable IV. > > Ok. I'll verify that the second half of the IV is zeroed. > > One last thing that I'm not sure of is what string to place in > cra_ablkcipher.geniv field. "eseqiv" seems wrong if plain/plain64 > are the IVs that XTS is designed for. Right. But since currently dm-crypt does not use .givencrypt and deals with IV generation by itself, we're safe. When dm-crypt IV generation will be moved to crypto, we'll have to revisit this. While here: note that xts-talitos supports only two key lengths - 256 and 512 bits. There are tcrypt speed tests that check also for 384-bit keys (which is out-of-spec, but still...), leading to a "Key Size Error" - see below (KSE bit in AESU Interrupt Status Register is set) testing speed of async xts(aes) (xts-aes-talitos) encryption [...] test 5 (384 bit key, 16 byte blocks): talitos ffe30000.crypto: CDPR is NULL, giving up search for offending descriptor talitos ffe30000.crypto: AESUISR 0x00000000_00000200 talitos ffe30000.crypto: DESCBUF 0x64300011_00000000 talitos ffe30000.crypto: DESCBUF 0x00000000_00000000 talitos ffe30000.crypto: DESCBUF 0x00100000_00000000 talitos ffe30000.crypto: DESCBUF 0x00300000_00000000 talitos ffe30000.crypto: DESCBUF 0x00100000_00000000 talitos ffe30000.crypto: DESCBUF 0x00100000_00000000 talitos ffe30000.crypto: DESCBUF 0x00100000_00000000 talitos ffe30000.crypto: DESCBUF 0x00000000_00000000 encryption() failed flags=0 So for xts, driver must enforce 256/512 bit key lengths and return CRYPTO_TFM_RES_BAD_KEY_LEN in all other cases. Or a SW fallback could be used for the other cases, but I don't think it's worth the effort since these are non-standard. Horia -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
