Talk:Message authentication code

message: This article needs to contain a succinct statement of the properties a MAC function needs to have to be considered secure. The text describes only one property, resistance to "existential forgery under chosen-plaintext attacks", which appears to be strictly easier to satisfy than collision resistance for hash functions. However, if that was the whole requirement, the function f_k(M) = H(M) where H is a good hash function and f_k(M) ignores k (!), would be a good MAC, which is not the case. Thus there must be more requirements. What are they, exactly? Henning Makholm 20:11, 9 February 2007 (UTC)
replies: text: The attacker has access to an oracle which produces a valid MAC tag given a message.  They make q queries of the oracle, then they output a (message, tag) pair and exit.  They succeed if the pair is valid and not one that was produced by the oracle. — ciphergoth 11:34, 22 February 2007 (UTC)
replies: text:  That makes sense. I have attempted to edit the article accordingly. Did I get it approximately right? –Henning Makholm 19:02, 22 February 2007 (UTC)
thread_title:  When is a MAC secure? 

message: The article implies that security from existential forgery means that two different messages should not produce the same tag. However, existential forgery[] actually means that an attacker is able to produce a valid message-tag pair, and does not have to show a collision.
Abejohnny 00:12, 22 February 2007 (UTC)
replies: text: Yes, this is definitely an error. — ciphergoth 11:19, 22 February 2007 (UTC)
thread_title:  Resisting existential forgery 

message: :Category:Message authentication codes is itself a category within :Category:Cryptographic algorithms which is in turn is a category within :Category:Cryptography. — Robert Greer (talk) 14:43, 6 March 2009 (UTC)
thread_title:  [[:Category:Cryptography]] ''vs.'' [[:Category:Cryptographic algorithms]] ''vs.'' [[:Category:Message authentication codes]]  

message: Once the executable code modification is possible, any symmetric encryption (including MAC) that uses software is not useful anymore. This is very trivial and not MAC specific, and I do not think it should be mentioned here - perhaps, on a more generic page? Dimawik (talk) 04:37, 28 September 2009 (UTC)
replies: text: Definitely not! Cryptography is about securing the communication channel, not the communication entities. If you can compromise such entity (through code exploits, stealing keys, whatever) security is trivially void. No need to mention that. Nageh (talk) 09:42, 28 September 2009 (UTC)
thread_title:  Code modification 

message: The MAC.svg appears correctly formatted, but the auto-generated thumbnail (MAC.svg.png) is not. Dallasvaughan (talk) 16:01, 10 November 2009 (UTC)
thread_title:  Bad SVG -> PNG thumbnail generation 

message: It would help to have a discussion of the issues around combining MACs and encryption.  For example, sign-then-encrypt vs encrypt-then sign.  See for example http://world.std.com/~dtd/sign_encrypt/sign_encrypt7.html, which mostly discusses the asymmetric signature-and-encryption case.  — Preceding unsigned comment added by 17.209.4.116 (talk) 19:07, 6 June 2011 (UTC)
replies: text: No otp or code or verify 2404:3C00:353E:E6E0:6CC1:F68F:7DA2:F3A1 (talk) 02:36, 25 August 2023 (UTC)
thread_title:  encrypt-and-authenticate 

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