[Cryptography] The paranoid approach to crypto-plumbing

Sandy Harris sandyinchina at gmail.com
Tue Sep 17 11:41:33 EDT 2013

On Mon, Sep 16, 2013 at 12:44 PM, Bill Frantz <frantz at pwpconsult.com> wrote:

> Symmetric encryption:
>   Two algorithms give security equal to the best of them. Three
>   protect against meet-in-the-middle attacks. Performing the
>   multiple encryption at the block level allows block cyphers to
>   be combined with stream cyphers. RC4 may have problems, but
>   adding it to the mix isn't very expensive.

A paper of mine on combining a stream cipher with a block
cipher: http://eprint.iacr.org/2008/473

AES-256 uses 14 rounds vs. 10 for AES-128, so it is about
40% slower. Given 256 bits of key and a stream cipher that
is 5x faster than AES, you can use AES-128 and have 128
bits to key the stream cipher. AES-128 plus whitening that
changes for every block (two 128-bit blocks of stream
cipher output) has roughly the same cost as AES-256.

There are several ways to reduce the cost and/or increase
the security from there; see the paper for details.

I am still working on this notion and will have a new and
much improved version of that paper sometime this year.
Anyone I know moderately well who wants to review it
can contact me off-list for the current draft.

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