Secure cryptoprocessor

A secure cryptoprocessor is a dedicated computer on a chip or microprocessor for carrying out cryptographic operations, embedded in a packaging with multiple physical security measures, which give it a degree of tamper resistance. Unlike cryptographic processors that output decrypted data onto a bus in a secure environment, a secure cryptoprocessor does not output decrypted data or decrypted program instructions in an environment where security cannot always be maintained.

The purpose of a secure cryptoprocessor is to act as the keystone of a security subsystem, eliminating the need to protect the rest of the subsystem with physical security measures.

Smartcards are probably the most widely deployed form of secure cryptoprocessor, although more complex and versatile secure cryptoprocessors are widely deployed in systems such as Automated teller machines, TV set-top boxes, military applications, and high-security portable communication equipment. Some secure cryptoprocessors can even run general-purpose operating systems such as Linux inside their security boundary. Cryptoprocessors input program instructions in encrypted form, decrypt the instructions to plain instructions which are then executed within the same cryptoprocessor chip where the decrypted instructions are inaccessibly stored. By never revealing the decrypted program instructions, the cryptoprocessor prevents tampering of programs by technicians who may have legitimate access to the sub-system data bus. This is known as bus encryption. Data processed by a cryptoprocessor is also frequently encrypted.

The Trusted Platform Module (TPM) is an implementation of a secure cryptoprocessor that brings the notion of trusted computing to ordinary PCs by enabling a secure environment. Present TPM implementations focus on providing a tamper-proof boot environment, and persistent and volatile storage encryption.

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