High Quality Content by WIKIPEDIA articles! The IBM 4764 Cryptographic Coprocessor is a secure cryptoprocessor that performs cryptographic operations used by application programs and by communications such as SSL private key transactions associated with SSL digital certificates. Each coprocessor includes a tamper-responding hardware security module (HSM) that provides secure storage for storing master keys and other sensitive data. The HSM has been certified to meet FIPS 140-2 Level 4 security requirements. The coprocessor is supported on all IBM server platforms including System z (mainframe), System i, System p, and System x (Linux or Microsoft Windows). On System z, it is called the "Crypto Express2".