SHA

What Is SHA?

Secure Hash Algorithm (SHASHACryptographyNIST hash functions for smart card integrity and signatures.Click to view →) is a family of NIST-standardized cryptographic hash functions that produce fixed-size digests from arbitrary-length input data. In smart card systems, SHA hashes are fundamental to digital signatures, message authentication, key derivation, and data integrity verification. Every time a smart card signs a document, verifies a certificate, or computes a MAC, a SHA hash function is involved.

SHA Variants in Smart Cards

How SHA Is Used on Smart Cards

SHA appears at multiple layers of smart card security:

• Digital signatures -- when a card performs an RSA or ECC signature, it first hashes the data using SHA-256 (or SHA-384), then signs the hash. The small, fixed-size digest is what the asymmetric algorithm actually operates on.
• Certificate verification -- verifying a certificate chain requires hashing the certificate body and comparing it against the issuer's signature. The card performs this when validating CVC certificates during terminal authentication.
• Message authentication -- HMAC-SHA-256 and CMAC (which internally uses AES) are used to compute MACs for secure messaging integrity.
• Key derivation -- SCP03 and PACE use SHA-based key derivation functions (KDFs) to derive session keys from shared secrets.

Hardware Acceleration

Smart card crypto coprocessors typically include dedicated SHA accelerators that process data at 5-20 MB/s, far faster than software computation on the card's CPU. This is important because hash operations are frequently invoked -- a single EMV transaction may require 10-20 SHA-256 computations for certificate verification, data authentication, and MAC generation.

SHA-1 Deprecation

SHA-1 has been cryptographically broken (practical collision attacks since 2017) and is deprecated for all security-critical smart card applications:

• EMV -- migrating from SHA-1 to SHA-256 for offline data authentication
• ePassport -- ICAO recommends SHA-256 or higher for new document signing certificates
• FIPS 201 -- prohibits SHA-1 for PIVPIVIdentityUS federal identity card standard.Click to view → digital signatures

Legacy cards with SHA-1 certificates remain in circulation but are being replaced on natural lifecycle schedules.