3 ms·
> You keep saying "the Galois Field" as if that was a thing You're kidding, right? You've never looked at how GCM-mode works? The entire set of math is inside
by dragontamer 4y ago
> You keep saying "the Galois Field" as if that was a thing
You're kidding, right? You've never looked at how GCM-mode works? The entire set of math is inside of the GF(2^128) field. That's why its called a Galois Counter Mode.
I don't think anyone should be implementing their own GCM mode. Its very subtle and potentially full of traps. CBC on the other hand is pretty dumb and simple, and surprisingly secure and robust
> Vulnerabilities in CBC systems were for a long time during the 2000s the most common crypto vulnerabilities on the Internet. There are more things that go wrong with CBC mode than just forgetting to authenticate it!
If they're so common, you shouldn't have much of an issue naming one such vulnerability.
- tptacek 4y agoI think some of my comment went over your head.
- devman0 4y agoBEAST and POODLE were both high profile attacks against how SSL used CBC.
- dragontamer 4y agoBut neither were attacks on CBC itself. That is to say: to "fix" BEAST or POODLE, you don't change a lick of CBC code at all.
- tptacek 4y ago[flagged]
- vengefulduck 4y agoThe math used in AES (Rijndael) utilize operations in GF(2^8) tho, so you're doing operations using Galois fields whether your utilizing GCM or CBC. I don't really see how adding the GCM mode utilizing GF(2^128) on top is significantly more difficult or error prone than implementing the AES block cipher itself. You should still be familiar with operations over Galois fields regardless if you've for some reason (foolishly imo) decided you want to implement AES cryptographic primitives on your own. Regardless there's no good reason not to use a vetted open source implementation instead, preferably with an even higher level of abstraction so your not having to worry about ciphers or modes of operation at all[1]. [1] https://doc.libsodium.org/secret-key_cryptography/secretbox https://doc.libsodium.org/secret-key_cryptography/secretbox
- dragontamer 4y agoThe library used in this Javascript widget has AES already implemented, but not GCM mode. > Regardless there's no good reason not to use a vetted open source implementation instead, preferably with an even higher level of abstraction so your not having to worry about ciphers or modes of operation at all[1]. I think that's generally the preferred solution, yes.