Multiple keys/methods per key exchange (e.g. multi-md5-sha1-md4 at libssh.org) Re: [PATCH] curve25519-sha256 at libssh.org key exchange proposal

[Roland Mainz]

On Tue, Sep 24, 2013 at 10:21 PM, Aris Adamantiadis <aris at 0xbadc0de.be> wrote:
[snip]
> I've worked this week on an alternative key exchange mechanism, in
> reaction to the whole NSA leaks and claims over cryptographic backdoors
> and/or cracking advances. The key exchange is in my opinion the most
> critical defense against passive eavesdropping attacks.
> I believe Curve25519 from DJB can give users a secure alternative to
> classical Diffie-Hellman (with fixed groups or group exchanges) and
> NIST-approved elliptic curves.
[snip]

... that reminds me of an old idea (note: I'm no expert in this
stuff... which means the idea may be total nonsense... or not... :-)
):
Is it usefull to combine multiple hash algorithms/methods for a key exchange ?

The idea would be to use something like "md5" and "sha1" in a key
exchange (and append the hash sums) ... individually there are
obsolete and more or less cracked or have serious weaknesses, but if
the hash sums are combined (e.g. appended... *NOT* XOR'ed !) it would
be near impossible to exploit the known weaknesses for reasonable
small data.

AFAIK the advantages would be:
- Existing hardware acceleration for md4/md5/sha1 can be used
- Even using something like md5+sha256 would mean additional
protection against weaknesses in either of the hash sum methods
- All algorithms can be executed in parallel (either different CPUs or
different crypto engines)

Note that the whole thing is not limited to two keys/methods, in
theory there could be something like
"multi-md5-sha1-md4-sha256 at libssh.org" to use md5, sha1, md4 and
sha256 hash sums.

Question is now... how mad/bad is the idea ?

----

Bye,
Roland

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