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Security Fundamentals & Crypto · Foundational

Secure Hash Algorithm 2 (SHA-2)

NIST family of hash functions including SHA-224, SHA-256, SHA-384, and SHA-512.

Definition

SHA-2 (FIPS 180-4) was designed by the NSA and published in 2001. It uses a Merkle-Damgard construction, which is susceptible to length-extension attacks if used naively as a MAC. SHA-256 and SHA-384 are the most widely used hashes today in TLS, certificates, and code signing.

Example

Certificates today are typically signed with sha256WithRSAEncryption or ecdsa-with-SHA384.

Exam tip

The number after SHA- is the digest size in bits; use HMAC rather than hash(key||message).

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