S2K Usage Octet,Shorthand,Encryption Parameter Fields,Encryption,Generate?,Reference
0,Unprotected,-,"v3 or v4 keys: [cleartext secrets || check(secrets)]
        v6 keys: [cleartext secrets]",Yes,[RFC9580]
"Known symmetric cipher algo ID (see [RFC9580, Section 9.3])",LegacyCFB,IV,"CFB(MD5(passphrase), secrets || check(secrets))",No,[RFC9580]
253,AEAD,"params-length (v6-only), cipher-algo, AEAD-mode, S2K-specifier-length (v6-only), S2K-specifier, nonce","AEAD(HKDF(S2K(passphrase), info), secrets, packetprefix)",Yes,[RFC9580]
254,CFB,"params-length (v6-only), cipher-algo, S2K-specifier-length (v6-only), S2K-specifier, IV","CFB(S2K(passphrase), secrets || SHA1(secrets))",Yes,[RFC9580]
255,MalleableCFB,"cipher-algo, S2K-specifier, IV","CFB(S2K(passphrase), secrets || check(secrets))",No,[RFC9580]