this.signKey = deriveKey(mk, C2S_SIGN_CONSTANT);
        this.verifyKey = deriveKey(mk, S2C_SIGN_CONSTANT);

        if (log.isDebugEnabled()) {
            log.debug("Sign key is " + Hexdump.toHexString(this.signKey));
            log.debug("Verify key is " + Hexdump.toHexString(this.verifyKey));
        }

        this.sealClientKey = deriveKey(mk, C2S_SEAL_CONSTANT);