In the authenticated encryption mode GCM (Galois Counter Mode), the CTR (counter) mode for data encryption that has no feedback path can easily be pipelined to boost the operating frequency of a hardware implementation. However, the hash function for the authentication tag generation performs multiply-add operations sequentially by chaining the result in the previous cycle, and this becomes the critical path in the high-speed GCM hardware. Therefore, we propose a high-speed pipelined hardware architecture for GCM in conjunction with a pipelined multiply-adder on a Galois field GF(2 128). This architecture was implemented with a 4-stage pipelined multiply-adder and a 56-stage pipelined AES (Advanced Encryption Standard) circuit by using a 0.13-um CMOS standard cell library. This implementation showed very high throughput of 54.94 Gbps with 272 Kgates for the key lengths of 128, 192, and 256 bits. The high hardware efficiency (throughput/gate) of 201.75 Kbps/gate is also an improvement over prior art.