hkdf

On-chain HKDF-SHA256 key derivation

Derive a 32-byte key with the HKDF precompile at 0x68.

Overview

hkdf() and async_hkdf() accept arbitrary input key material (ikm) and return a Bytes32 derived key.

Signature

def hkdf(
    w3: Web3,
    ikm: bytes,
) -> Bytes32

async def async_hkdf(
    w3: AsyncWeb3,
    ikm: bytes,
) -> Bytes32

Parameters

Parameter	Type	Required	Description
w3	Web3 / AsyncWeb3	Yes	Connected Seismic client
ikm	bytes	Yes	Input key material

Returns

Type	Description
Bytes32	32-byte derived key

Examples

Basic Usage

from seismic_web3 import create_public_client
from seismic_web3 import precompiles as sp

w3 = create_public_client("https://gcp-1.seismictest.net/rpc")

key = sp.hkdf(w3, b"input key material")
print(key.to_0x_hex())

Context Separation

master = b"shared-secret"
encryption_key = sp.hkdf(w3, master + b"\x01encryption")
auth_key = sp.hkdf(w3, master + b"\x02auth")
assert encryption_key != auth_key

Async Usage

from seismic_web3 import create_async_public_client
from seismic_web3 import precompiles as sp

async def main():
    w3 = create_async_public_client("https://gcp-1.seismictest.net/rpc")
    key = await sp.async_hkdf(w3, b"async input")
    print(key.to_0x_hex())

Gas Cost

The SDK computes gas as:

from math import ceil

linear = 3000 + ceil(len(ikm) / 32) * 12
total_gas = 2 * linear + 120

Examples:

• len(ikm)=0: 6120

• len(ikm)=32: 6144

Notes

• Deterministic: the same ikm always produces the same output.

• Good for deriving protocol keys from shared secrets.

• Not a password hashing function; use argon2/bcrypt for password storage.

See Also

• HKDF — Precompiles Reference

• ecdh

• aes-gcm-encrypt

• rng