public Key generateNewKey() {
        return generateNewKey(getKeySize());
    }
Generates a new {@link java.security.Key Key} suitable for this CipherService's {@link #getAlgorithmName() algorithm}
by calling {@link #generateNewKey(int) generateNewKey(128)} (uses a 128 bit size by default).

@return a new {@link java.security.Key Key}, 128 bits in length.
src/main/java/org/apache/shiro/crypto/cipher/AbstractSymmetricCipherService.java