IETF logoEmil Lundberg and I have published the COSE Algorithms for Two-Party Signing specification. Its abstract is:

This specification defines COSE algorithm identifiers used when the signing operation is performed cooperatively between two parties. When performing two-party signing, the first party typically hashes the data to be signed and the second party signs the hashed data computed by the first party. This can be useful when communication with the party holding the signing private key occurs over a limited-bandwidth channel, such as NFC or Bluetooth Low Energy (BLE), in which it is infeasible to send the complete set of data to be signed. The resulting signatures are identical in structure to those computed by a single party, and can be verified using the same verification procedure without additional steps to preprocess the signed data.

A motivating use case for this is for WebAuthn/FIDO2 Authenticators to use when signing application data, as described in the proposed WebAuthn signing extension. Parts of this spec’s content were previously in the Asynchronous Remote Key Generation (ARKG) algorithm spec, which we’ve also been updated.

I plan to talk about the spec during IETF 122 in Bangkok. I hope to see many of you there!

The specification is available at:

This work was supported by the SIROS Foundation.