Provably Secure Public-Key Encryption for Length-Preserving Chaumian Mixes [chapter]

Bodo Möller
2003 Lecture Notes in Computer Science  
Mix chains as proposed by Chaum allow sending untraceable electronic e-mail without requiring trust in a single authority: messages are recursively public-key encrypted to multiple intermediates (mixes), each of which forwards the message after removing one layer of encryption. To conceal as much information as possible when using variable (source routed) chains, all messages passed to mixes should be of the same length; thus, message length should not decrease when a mix transforms an input
more » ... sage into the corresponding output message directed at the next mix in the chain. Chaum described an implementation for such length-preserving mixes, but it is not secure against active attacks. We show how to build practical cryptographically secure lengthpreserving mixes. The conventional definition of security against chosen ciphertext attacks is not applicable to length-preserving mixes; we give an appropriate definition and show that our construction achieves provable security.
doi:10.1007/3-540-36563-x_17 fatcat:666be75uy5ckxggbftxvtatlde