## Atomic Proxy Cryptography

### Matt Blaze

### AT&T Shannon Laboratory

This talk introduces *atomic proxy cryptography*, in which an atomic proxy function, in conjunction with a public proxy key, converts ciphertext (messages in a public key encryption scheme or signatures in a digital signature scheme) for one key ($k_1$) into ciphertext for another ($k_2$). Proxy keys, once generated, may be made public and proxy functions applied in untrusted environments. Various kinds of proxy functions might exist; {\em symmetric} atomic proxy functions assume that the holder of $k_2$ unconditionally trusts the holder of $k_1$, while {\em asymmetric} proxy functions do not. It is not clear whether proxy functions exist for previous public-key cryptosystems. Several new public-key cryptosystems with symmetric proxy functions are described: an encryption scheme, which is at least as secure as Diffie-Hellman, an identification scheme, which is at least as secure as the discrete log, and a signature scheme derived from the identification scheme via a hash function.

Full paper available.

This is joint work with Martin Strauss.

Matt Blaze`, Atomic Proxy Cryptography`

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```Gates 498, 10/20/98, 4:15 PM