Roadmap towards PQC support (ML-DSA)

Yubico has recently demo'ed a Yubikey with ML-DSA support for FIDO usage. Time to start thinking what it takes to make the code fit for PQC support.

• Keys are extracted using the library web-auth/cose-lib. That library does not currently support ML-DSA keys (https://github.com/web-auth/cose-lib/blob/4.6.x/src/Key/Key.php)
• actual signature checks are done with openssl_verify and the public key loaded with openssl_pkey_get_public. Currently unknown whether recent PHP supports handling of ML-DSA keys.
• underlying openssl library in version 3.5.0+ DOES support ML-DSA keys.

I will run some tests with openssl and the openssl_* functions in PHP to determine how far we can get on that front.

Inizia dalla gestione delle chiavi in src/Key/Key.php di web-auth/cose-lib e dall'uso di openssl_verify e openssl_pkey_get_public da parte del modulo. Verifica se PHP è in grado di elaborare chiavi ML-DSA con OpenSSL 3.5.0 o versioni successive, quindi documenta i risultati della compatibilità e il lavoro concreto necessario per supportarle.