WebAuthn

Git Source

Authors: Solady (https://github.com/vectorized/solady/blob/main/src/utils/WebAuthn.sol), Modified from Daimo WebAuthn (https://github.com/daimo-eth/p256-verifier/blob/master/src/WebAuthn.sol), Modified from Coinbase WebAuthn (https://github.com/base-org/webauthn-sol/blob/main/src/WebAuthn.sol)

WebAuthn helper.

Functions

verify

We do not verify all the steps as described in the specification, only ones relevant to our context. Please carefully read through this list before usage.

Specifically, we do verify the following:

• Verify that authenticatorData (which comes from the authenticator, such as iCloud Keychain) indicates a well-formed assertion with the "User Present" bit set. If requireUserVerification is set, checks that the authenticator enforced user verification. User verification should be required if, and only if, options.userVerification is set to required in the request.
• Verifies that the client JSON is of type "webauthn.get", i.e. the client was responding to a request to assert authentication.
• Verifies that the client JSON contains the requested challenge.
• Verifies that (r, s) constitute a valid signature over both the authData and client JSON, for public key (x, y).

We make some assumptions about the particular use case of this verifier, so we do NOT verify the following:

• Does NOT verify that the origin in the clientDataJSON matches the Relying Party's origin: it is considered the authenticator's responsibility to ensure that the user is interacting with the correct RP. This is enforced by most high quality authenticators properly, particularly the iCloud Keychain and Google Password Manager were tested.
• Does NOT verify That topOrigin in clientDataJSON is well-formed: We assume it would never be present, i.e. the credentials are never used in a cross-origin/iframe context. The website/app set up should disallow cross-origin usage of the credentials. This is the default behavior for created credentials in common settings.
• Does NOT verify that the rpIdHash in authenticatorData is the SHA-256 hash of the RP ID expected by the Relying Party: this means that we rely on the authenticator to properly enforce credentials to be used only by the correct RP. This is generally enforced with features like Apple App Site Association and Google Asset Links. To protect from edge cases in which a previously-linked RP ID is removed from the authorized RP IDs, we recommend that messages signed by the authenticator include some expiry mechanism.
• Does NOT verify the credential backup state: this assumes the credential backup state is NOT used as part of Relying Party business logic or policy.
• Does NOT verify the values of the client extension outputs: this assumes that the Relying Party does not use client extension outputs.
• Does NOT verify the signature counter: signature counters are intended to enable risk scoring for the Relying Party. This assumes risk scoring is not used as part of Relying Party business logic or policy.
• Does NOT verify the attestation object: this assumes that response.attestationObject is NOT present in the response, i.e. the RP does not intend to verify an attestation.

function verify(
        bytes memory challenge,
        bool requireUserVerification,
        WebAuthnAuth memory auth,
        bytes32 x,
        bytes32 y
    ) internal view returns (bool result);

Parameters

Returns

verify

function verify(
        bytes memory challenge,
        bool requireUserVerification,
        bytes memory authenticatorData,
        string memory clientDataJSON,
        uint256 challengeIndex,
        uint256 typeIndex,
        bytes32 r,
        bytes32 s,
        bytes32 x,
        bytes32 y
    ) internal view returns (bool);

Parameters

Returns

encodeAuth

function encodeAuth(WebAuthnAuth memory auth) internal pure returns (bytes memory);

Parameters

Returns

tryDecodeAuth

function tryDecodeAuth(bytes memory encodedAuth)
        internal
        pure
        returns (WebAuthnAuth memory decoded);

Parameters

Returns

tryEncodeAuthCompact

abi.encodePacked(
uint16(auth.authenticatorData.length),
bytes(auth.authenticatorData),
bytes(auth.clientDataJSON),
uint16(auth.challengeIndex),
uint16(auth.typeIndex),
bytes32(auth.r),
bytes32(auth.s)
)

function tryEncodeAuthCompact(WebAuthnAuth memory auth)
        internal
        pure
        returns (bytes memory result);

Parameters

Returns

tryDecodeAuthCompact

function tryDecodeAuthCompact(bytes memory encodedAuth)
        internal
        pure
        returns (WebAuthnAuth memory decoded);

Parameters

Returns

tryDecodeAuthCompactCalldata

function tryDecodeAuthCompactCalldata(bytes calldata encodedAuth)
        internal
        pure
        returns (WebAuthnAuth memory decoded);

Parameters

Returns

Structs

WebAuthnAuth

struct WebAuthnAuth {
        // The WebAuthn authenticator data.
        // See: https://www.w3.org/TR/webauthn-2/#dom-authenticatorassertionresponse-authenticatordata.
        bytes authenticatorData;
        // The WebAuthn client data JSON.
        // See: https://www.w3.org/TR/webauthn-2/#dom-authenticatorresponse-clientdatajson.
        string clientDataJSON;
        // Start index of "challenge":"..." in `clientDataJSON`.
        uint256 challengeIndex;
        // Start index of "type":"..." in `clientDataJSON`.
        uint256 typeIndex;
        // The r value of secp256r1 signature.
        bytes32 r;
        // The s value of secp256r1 signature.
        bytes32 s;
    }

Properties