*/
    private PacMac() {
        // Utility class
    }

    /**
     *
     */
    private static final String HMAC_KEY = "HMAC";
    private static final byte[] MD5_CONSTANT = "signaturekey\0".getBytes(StandardCharsets.US_ASCII);
    private static final byte[] ZERO_IV = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };

    /**
     * Calculates a MAC using the ARCFOUR-HMAC-MD5 algorithm.

    *   Add 5D support to `SLICE` op.
    *   TFLite Supports SingatureDef:
        *   TFLiteConverter exports models with SignatureDef
        *   Interpreter supports getting a list of signatures and getting
            callable function for a given signaturedef.
    *   Add int8 support for `ReshapeV2`.
    *   Add experimental support for optimization with sparsity.