protected static SecureRandom getDefaultSecureRandom() {
        try {
            return java.security.SecureRandom.getInstance(RANDOM_NUM_GENERATOR_ALGORITHM_NAME);
        } catch (java.security.NoSuchAlgorithmException e) {
            log.debug("The SecureRandom SHA1PRNG algorithm is not available on the current platform.  Using the " +
                    "platform's default SecureRandom algorithm.", e);
            return new java.security.SecureRandom();
        }
    }
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