ParagonIE_Sodium_Core_Ed25519::sign_detached

    public static function sign_detached($message, $sk)
    {
        # crypto_hash_sha512(az, sk, 32);
        $az =  hash('sha512', self::substr($sk, 0, 32), true);

        # az[0] &= 248;
        # az[31] &= 63;
        # az[31] |= 64;
        $az[0] = self::intToChr(self::chrToInt($az[0]) & 248);
        $az[31] = self::intToChr((self::chrToInt($az[31]) & 63) | 64);

        # crypto_hash_sha512_init(&hs);
        # crypto_hash_sha512_update(&hs, az + 32, 32);
        # crypto_hash_sha512_update(&hs, m, mlen);
        # crypto_hash_sha512_final(&hs, nonce);
        $hs = hash_init('sha512');
        hash_update($hs, self::substr($az, 32, 32));
        hash_update($hs, $message);
        $nonceHash = hash_final($hs, true);

        # memmove(sig + 32, sk + 32, 32);
        $pk = self::substr($sk, 32, 32);

        # sc_reduce(nonce);
        # ge_scalarmult_base(&R, nonce);
        # ge_p3_tobytes(sig, &R);
        $nonce = self::sc_reduce($nonceHash) . self::substr($nonceHash, 32);
        $sig = self::ge_p3_tobytes(
            self::ge_scalarmult_base($nonce)
        );

        # crypto_hash_sha512_init(&hs);
        # crypto_hash_sha512_update(&hs, sig, 64);
        # crypto_hash_sha512_update(&hs, m, mlen);
        # crypto_hash_sha512_final(&hs, hram);
        $hs = hash_init('sha512');
        hash_update($hs, self::substr($sig, 0, 32));
        hash_update($hs, self::substr($pk, 0, 32));
        hash_update($hs, $message);
        $hramHash = hash_final($hs, true);

        # sc_reduce(hram);
        # sc_muladd(sig + 32, hram, az, nonce);
        $hram = self::sc_reduce($hramHash);
        $sigAfter = self::sc_muladd($hram, $az, $nonce);
        $sig = self::substr($sig, 0, 32) . self::substr($sigAfter, 0, 32);

        try {
            ParagonIE_Sodium_Compat::memzero($az);
        } catch (SodiumException $ex) {
            $az = null;
        }
        return $sig;
    }