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Re: Why is blowfish so slow? Other fast algorithms?
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In article <[email protected]>,
David Mazieres <[email protected]> wrote:
> The problem with RC4 is that it works in OFB only. If I need data
> integrity in the face of known plaintext, I will need to compute a MAC
> in paralell with the encryption which could significantly slow things
> down.
If you want authentication, you must use a crypto-strength MAC.
Encryption (be it RC4, DES, etc.) is not enough.
> With a block cypher in CFB, I can just re-encrypt the last
> block of data.
False. CFB has limited error propagation, so if I modify any block
before the next-to-last, it will not show up with your method.
This seems to be a really common error.
If you want message integrity guarantees, you must use a MAC. Always.
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