}
        for (int i = length; i < BLOCK_LENGTH; i++) {
            ipad[i] = IPAD;
            opad[i] = OPAD;
        }
        try {
            md5 = MessageDigest.getInstance("MD5");
        } catch (Exception ex) {
            throw new IllegalStateException(ex.getMessage());
        }
        engineReset();
    }

    private HMACT64(HMACT64 hmac) throws CloneNotSupportedException {
        super("HMACT64");

        byte[] digest = this.md5.digest();
        this.md5.update(this.opad);
        this.md5.update(digest);
        try {
            return this.md5.digest(buf, offset, len);
        }
        catch ( Exception ex ) {
            throw new IllegalStateException();
        }
    }


    @Override
    protected int engineGetDigestLength () {
        return this.md5.getDigestLength();
    }