HMAC-SHA-256

Overview & Cryptographic Context

HMAC (Hash-based Message Authentication Code), standardized in RFC 2104 and NIST FIPS 198-1, constructs a PRF and message authentication code from an unkeyed cryptographic hash function H using two nested passes with inner (0x36) and outer (0x5c) XOR pads:

HMAC(K, m) = H((K' ⊕ opad) ‖ H((K' ⊕ ipad) ‖ m))

Because Merkle-Damgård hashes like SHA-256 are vulnerable to length-extension attacks when used naively as H(K ‖ m), the outer hash invocation over the inner 32-byte digest prevents an attacker from appending data without knowing K. This workflow reproduces RFC 4231 §4.3 (Test Case 2), authenticating the ASCII phrase "what do ya want for nothing?" under the 4-byte ASCII key "Jefe" (zero-padded internally to the 64-byte SHA-256 block size B).

Pipeline Architecture & Wiring Flow

1. Key & Message Ingress (Workflow Input): Supplies the secret Key (4 bytes, 4a656665) and the message Data (28 bytes).
2. Keyed Hash Computation (HMAC Generator): Configured with algorithm = "SHA-256". The node automatically normalizes keys shorter or longer than 64 bytes per RFC 2104 before computing the 32-byte tag.
3. MAC Output (Workflow Output): Emits the resulting 32-byte (256-bit) authentication code on the MAC output port.

Nodes & Configuration

Node reference →

Inputs, Outputs & Test Vector Verification

Verification Source: RFC 4231 §4.3 (Test Case 2, HMAC-SHA-256)

Inputs

Expected Outputs