On 2012-02-20 2:08 AM, Florian Weimer wrote:
>> Can somebody explain me how this so-called Homomorphic split-key
>> encryption works?
Homomorphic means you combine the keys without finding out the key that
you are combining - Everyone gives you an encrypted copy of their key
fragment, and when you are done, you have an encrypted copy of the
combined key.
> Isn't this just a protocal which performs a cryptographic primitive
> using split key material, without actually recombining the keys?
> (Traditional Shamir secret sharing needs a trust party for key
> recombination.)
>
> If yes, you might want to look for "RSA Threshold Cryptography" and
> similar work.
My understanding is that RSA Threshold always requires a "trusted"
party, which makes it useless. If you have a party that is actually
trusted, just let him count the votes or whatever. The cryptography
does not do you any good.
The only protocol that I am aware of that performs cryptographic
operations on a split key with needing a trusted party, uses Gap Diffie
Hellman groups.
All known Gap Diffie Hellman Groups consist of an elliptic curve which
supports a bilinear pairing from the curve to integers modulo some large
prime.
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