secp256k1 Sign

Sign a 32-byte message hash using a secp256k1 private key. Produces a 65-byte signature in the (r, s, v) format. This allows contracts to generate signatures on-chain -- something that is normally only possible off-chain with a user's wallet.

This precompile gives the contract the ability to sign arbitrary messages. The private key used must be one the contract has access to (e.g., derived from a seed stored in shielded storage). It does not use the caller's private key.

Input

Raw bytes in the following layout (64 bytes total):

Offset	Field	Type	Description
[0:32]	private key	32 bytes	secp256k1 private key
[32:64]	message hash	32 bytes	Hash of the message to sign

Output

Bytes	Type	Description
signature	65 bytes	Signature in (r, s, v) format

Use cases

• Generating on-chain attestations or proofs

• Building contracts that can act as signers (e.g., smart-contract wallets)

• Creating signed messages for cross-chain verification

Examples

Built-in helper

function secp256k1_sign(sbytes32 secretKey, bytes32 messageHash) view returns (bytes memory);

bytes memory signature = secp256k1_sign(mySecretKey, msgHash);

Manual usage

function signMessage(
    bytes32 privateKey,
    bytes32 messageHash
) internal view returns (bytes memory) {
    (bool success, bytes memory result) = address(0x69).staticcall(
        abi.encodePacked(privateKey, messageHash)
    );
    require(success, "secp256k1 Sign precompile failed");
    return result;
}