public SecureRandom getSecureRandom() {
        return secureRandom;
    }
Returns 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.

@return 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.
crypto/cipher/src/main/java/org/apache/shiro/crypto/cipher/JcaCipherService.java