Subject: [Cfrg] Actual definition of proxy reencryption

From: Watson Ladd <[email-masked]>
Date: Sat, 23 Jul 2016 10:37:01 -0700

Dear all,

I'm reading through the CFRG slides and these lecture notes
(http://www.cs.jhu.edu/~susan/600.641/scribes/lecture17.pdf) on proxy
reencryption. It's not clear how useful this sort of scheme would be
for email lists, and comparing the complexity to reencrypting the
email to each recipient.

Perhaps there are protocols that could benefit, but I think it would
be best to have a working implementation of the protocol showing this
is useful before beginning to discuss systems that might be used.

Sincerely,
Watson

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From: David Núñez <[email-masked]>
Date: Sat, 23 Jul 2016 21:31:09 +0200

Regarding the definition of proxy re-encryption, I think the following 
is clear and precise:

Proxy Re-Encryption (PRE) is a type of public-key encryption that allows 
a proxy entity to transform ciphertexts encrypted under a delegator's 
public key into ciphertexts decryptable by a delegatee's private key. In 
order to do so, the proxy must be in possession of a re-encryption key 
generated by the delegator. In addition, the proxy cannot learn any 
information about the underlying message during the re-encryption 
process.

With respect to the utility of PRE, in general, the intended use is to 
perform secure access delegation to encrypted data. The goal is that the 
entity enforcing this delegation (i.e., the proxy) doesn't learn 
anything. The main use case besides encrypted email lists is secure data 
sharing in outsourced environments (e.g., the cloud).

If you are interested in prototype implementations of PRE schemes, the 
CHARM framework (https://github.com/JHUISI/charm) has working 
implementations of some schemes (disclaimer: I wrote that code).

Regards,
David