[Moderator's Note: please don't top post.... --Perry]
Commutativity is a beautiful and powerful property. See "On the power of
Commutativity in Cryptography" by Adi Shamir.
Semantic security is great and has given a new provable sense of
security, but commutative building blocks can be combined to build the
strangest protocols without going into deep mathematics, are better
suited for teaching crypto and for high-level protocol design. They are
like the "Lego" blocks of cryptography!
Now I'm working on an new untraceable e-cash protocol which has some
additional properties. And I'm searching for a secure commutable
signing primitive.
Best regards,
Sergio Lerner.
On 22/03/2010 09:56 a.m., Jonathan Katz wrote:
Sounds like a bad idea -- at a minimum, your encryption will be
deterministic.
What are you actually trying to achieve? Usually once you understand
that, you can find a protocol solving your problem already in the
crypto literature.
On Sun, 21 Mar 2010, Sergio Lerner wrote:
I looking for a public-key cryptosystem that allows commutation of
the operations of encription/decryption for different users keys
( Ek(Es(m)) = Es(Ek(m)) ).
I haven't found a simple cryptosystem in Zp or Z/nZ.
I think the solution may be something like the RSA analogs in
elliptic curves. Maybe a scheme that allows the use of a common
modulus for all users (RSA does not).
I've read on some factoring-based cryptosystem (like Meyer-Muller or
Koyama-Maurer-Okamoto-Vantone) but the cryptosystem authors say
nothing about the possibility of using a common modulus, neither for
good nor for bad.
Anyone has a deeper knowledge on this crypto to help me?
Best regards,
Sergio Lerner.
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