recipient function
Extracts the recipient's fingerprint from a COSE_Encrypt0 message without decrypting it.
This allows looking up the appropriate decryption key before attempting full decryption.
Returns the recipient's fingerprint from the protected header's kid field.
Implementation
xhpke.Fingerprint recipient({required Uint8List ciphertext}) =>
xhpke.FingerprintInternal.wrap(ffi.coseRecipient(ciphertext: ciphertext));