public static function deriveEncryptionKeyPair(HiddenString $password, string $salt, string $level = self::INTERACTIVE) : EncryptionKeyPair
{
$kdfLimits = self::getSecurityLevels($level);
// VERSION 2+ (argon2)
if (Util::safeStrlen($salt) !== \Sodium\CRYPTO_PWHASH_SALTBYTES) {
throw new CryptoException\InvalidSalt('Expected ' . \Sodium\CRYPTO_PWHASH_SALTBYTES . ' bytes, got ' . Util::safeStrlen($salt));
}
// Diffie Hellman key exchange key pair
$seed = \Sodium\crypto_pwhash(\Sodium\CRYPTO_BOX_SEEDBYTES, $password->getString(), $salt, $kdfLimits[0], $kdfLimits[1]);
$keyPair = \Sodium\crypto_box_seed_keypair($seed);
$secretKey = \Sodium\crypto_box_secretkey($keyPair);
// Let's wipe our $kp variable
\Sodium\memzero($keyPair);
return new EncryptionKeyPair(new EncryptionSecretKey(new HiddenString($secretKey)));
}