Question regarding common modulus on elliptic curve cryptosystems

Sergio Lerner sergiolerner at
Sun Mar 21 17:13:02 EDT 2010

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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