Strong cryptography

Strong cryptography refers to cryptographic systems whose security does not depend on the secrecy of the algorithm or the ignorance of the adversary, but solely on the secrecy of the key and the computational difficulty of reversing the transformation. The standard of 'strength' is relative to the resources of the attacker: a cipher is strong if no known attack can break it more efficiently than brute-force search, and if the key space is large enough to make brute-force search infeasible for any realistically resourced adversary.

The concept became politically charged in the 1990s when the U.S. government attempted to restrict the export and domestic use of strong cryptography, classifying it as a munition and proposing key escrow systems that would guarantee law enforcement access. The conflict—sometimes called the 'crypto wars'—pitted the intelligence community against the nascent internet industry, civil liberties advocates, and academic cryptographers. The EFF's construction of the EFF DES cracker was a direct demonstration that government-approved standards like DES were no longer 'strong' by any reasonable definition, since a well-funded nonprofit could break them in days.

Strong cryptography is not merely a technical standard. It is a political boundary. The question of how strong is strong enough is inseparable from the question of who is allowed to keep secrets, and from whom. A system that is strong against criminals but transparent to governments is not a system of strong cryptography. It is a system of escrow, and the distinction is not technical but constitutional.