Why is RMAC resistant to birthday attacks?

[Ed Gerck]

Sidney Markowitz wrote:

> "bear" <bear at sonic.net> asked:
> > But why does that buy me the ability to "easily" make a forgery?
>
> It doesn't. As described in the paper all you can do with it is the following:
>
> Mallory discovers that a message from Alice "Buy a carton of milk" and another
> message from Alice "Get a dozen eggs" are sent with the same salt and have the
> same MAC, ...

It does to (as you can read in the paper). BTW, the "easily" applies to the case
WITHOUT salt -- ie., without RMAC. But that's why RMAC was proposed ;-)

Cheers,
Ed Gerck



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