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I had never heard of this GCM mode for block ciphers, do any distro package OpenSSL with this mode activated by default?
by simias 13y ago
I had never heard of this GCM mode for block ciphers, do any distro package OpenSSL with this mode activated by default?
- djmdjm 13y agoIt's https://en.wikipedia.org/wiki/Galois_Counter_Mode https://en.wikipedia.org/wiki/Galois_Counter_Mode and IIRC it was added to OpenSSL in the 1.0.1 release. Don't let my hazy recollection be a substitute for checking your platform though :) (see some good recipes in this thread)
- rb12345 13y agoIt's used in TLS 1.2, so I'd assume any distros using OpenSSL 1.0.1 (which added TLS 1.2 support) would have it enabled.
- riquito 13y agoQuoting Matthew Green "the only people who hate GCM are those who've had to implement it. You see, GCM is CTR mode encryption with the addition of a Carter-Wegman MAC set in a Galois field. If you just went 'sfjshhuh?', you now understand what I'm talking about. Implementing GCM is a hassle in a way that most other AEADs are not. But if you have someone else's implementation -- say OpenSSL's -- it's a perfectly lovely mode." From an interesting read http://blog.cryptographyengineering.com/2012/05/how-to-choose-authenticated-encryption.html http://blog.cryptographyengineering.com/2012/05/how-to-choos...
- geofft 13y agoGCM is one of the authenticated-encryption modes, which means that in addition to encrypting the data, it also generates an authentication tag. It is somewhat like using a plain-encryption mode like CTR or CBC and also using a MAC like HMAC, but a single algorithm, so there's less complexity. Other authenticated-encryption block cipher modes include OCB and EAX. (Most of these are actually "authenticated encryption with associated data", which also let you add some cleartext data to the authentication tag without encrypting it.) I believe GCM support is new as of OpenSSL 1.0.