HKDF

HMAC-based Key Derivation Function (RFC 5869). Derives a 32-byte cryptographic key from input key material. Commonly used to turn a shared secret (from ECDH) into an encryption key suitable for AES-GCM.

The Seismic HKDF precompile uses hardcoded parameters: salt is None, info is a fixed internal string, and the output is always 32 bytes. The only user-supplied input is the raw key material.

Input

Field	Type	Description
input key material	bytes	Source key material (e.g., raw ECDH shared point)

Output

Bytes	Type	Description
derived key	32 bytes	Derived key material

Use cases

• Deriving AES encryption keys from shared secrets

• Key derivation with domain separation

Examples

Built-in helper

function hkdf(bytes memory input) view returns (bytes32);

bytes32 derivedKey = hkdf(inputKeyMaterial);

Manual usage

function deriveKey(bytes memory ikm) internal view returns (bytes32) {
    (bool success, bytes memory result) = address(0x68).staticcall(ikm);
    require(success, "HKDF precompile failed");
    require(result.length == 32, "Invalid HKDF output length");
    return bytes32(result);
}