>> > I suggest that you make these parameters to your CTR template. >> > So instead of requesting for "ctr(aes)", you could request for >> > "ctr(aes, 4, 8)" where 4 is the length of the nonce in the >> > counter block and 8 is the length of the IV. The counter >> > itself would then be calculated as block_size - 4 - 8. >> > >> Ok, pretty much had this coded up when it dawned on me >> maybe I should include the nonce as parameter too. >> Whenever you use ctr, it is a given you need the nonce. >> Couldn't the user of the api, separate the nonce from >> the key and pass it in the template? It would solve >> my problem about sometimes the keylen is bigger than >> max-key-length for the algorithm with the additional bytes >> for nonce. So, I could pass in ctr(aes, nonce, noncesize, ivsize). >> Let me know if this sounds ok or did I miss something important? > >It would be awkward to have the actual nonce as a parameter >because for IPsec at least it's negotiated through the same >process as the encryption key. > >More importantly, for the same "ctr(aes, 4, 8)" tuple, there >are many users (each SA would need two) while for if you >include the actual nonce then each tuple would be used by just >one SA. Ahhhhh, ok. Yes, you are right. I have another question regarding this change to using a tuple. The size of my counter is now, csize = blocksize - (noncesize + ivsize). rfc 3686 (CTR-AES for ESP) states in section 4, that the counter portion of the counter block be a 32-bit big endian. To keep code endian-neutral as I can, would it be appropriate if I only did this when my csize is 2, 4 or 8 bytes so I can easily use be16_to_cpu(), be32_to_cpu() and be64_to_cpu() respectively? And for all other sizes for csize, don't worry about this "endian" requirement, just store as is. Does it matter that I store the 32 bits as big endian? Regards, Joy - 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
