Capstone (cryptography)

In the context of cryptography, "Capstone" refers to a specific stream cipher developed as part of the Cryptographic Algorithm Verification Program (CAVP) sponsored by the Communications Security Establishment (CSE), the Canadian signals intelligence agency. Capstone is notable for its inclusion of several cryptographic algorithms, including the Skipjack encryption algorithm, the Diffie-Hellman key exchange protocol, and the Digital Signature Algorithm (DSA).

While the term "Capstone" can sometimes broadly refer to a final project or culmination of work in other fields, its cryptographic use specifically pertains to this suite of algorithms and security standards. Its prominence stems from its historical significance in U.S. government cryptographic initiatives and the subsequent declassification and publication of Skipjack after controversy surrounding its initial secrecy and use within the Clipper chip. The initiative surrounding Capstone and Clipper aimed to provide secure communications while retaining a government key escrow capability, a design aspect that faced considerable criticism from privacy advocates and security experts. Despite its original purpose, Capstone's legacy lies in its role as a case study for the complexities of balancing security, privacy, and government oversight in cryptographic systems.