protected SecureRandom ensureSecureRandom() {
        SecureRandom random = getSecureRandom();
        if (random == null) {
            random = getDefaultSecureRandom();
        }
        return random;
    }
Sets a source of randomness for encryption operations.  If one is not configured, and the underlying
algorithm needs one, the JDK {@code SHA1PRNG} instance will be used by default.

@param secureRandom a source of randomness for encryption operations.  If one is not configured, and the
                    underlying algorithm needs one, the JDK {@code SHA1PRNG} instance will be used by default.
src/main/java/org/apache/shiro/crypto/cipher/JcaCipherService.java