Key disclosure law

Key disclosure laws, also known as mandatory key disclosure, is legislation that requires individuals to surrender cryptographic keys to law enforcement. The purpose is to allow access to material for confiscation or digital forensics purposes and use it either as evidence in a court of law or to enforce national security interests. Similarly, mandatory decryption laws force owners of encrypted data to supply decrypted data to law enforcement.[1]

Nations vary widely in the specifics of how they implement key disclosure laws. Some, such as Australia, give law enforcement wide-ranging power to compel assistance in decrypting data from any party. Some, such as Belgium, concerned with self-incrimination, only allow law enforcement to compel assistance from non-suspects. Some require only specific third parties such as telecommunications carriers, certification providers, or maintainers of encryption services to provide assistance with decryption. In all cases, a warrant is generally required.

Theory and countermeasures

Mandatory decryption is technically a weaker requirement than key disclosure, since it is possible in some cryptosystems to prove that a message has been decrypted correctly without revealing the key. For example, using RSA public-key encryption, one can verify given the message (plaintext), the encrypted message (ciphertext), and the public key of the recipient that the message is correct by merely re-encrypting it and comparing the result to the encrypted message. Such a scheme is called undeniable, since once the government has validated the message they cannot deny that it is the correct decrypted message.[2]

As a countermeasure to key disclosure laws, some personal privacy products such as BestCrypt, FreeOTFE, and TrueCrypt have begun incorporating deniable encryption technology, which enable a single piece of encrypted data to be decrypted in two or more different ways, creating plausible deniability.[3][4] Another alternative is steganography, which hides encrypted data inside of benign data so that it is more difficult to identify in the first place.

A problematic aspect of key disclosure is that it leads to a total compromise of all data encrypted using that key in the past or future; time-limited encryption schemes such as those of Desmedt et al.[2] allow decryption only for a limited time period.