Question regarding common modulus on elliptic curve cryptosystems

Jonathan Katz jkatz at
Mon Mar 22 08:56:49 EDT 2010

[Moderator's Note: please don't top post... --Perry]

Sounds like a bad idea -- at a minimum, your encryption will be 

What are you actually trying to achieve? Usually once you understand that, 
you can find a protocol solving your problem already in the crypto 

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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