Efficient implementation of block ciphers is critical towards achieving both high security and high-speed processing. Numerous block ciphers have been proposed and implemented, using a wide and varied range of functional operations. As a result, it has become increasingly more difficult to develop a hardware architecture that allows the efficient and fast realization of a wide variety of block ciphers. In an effort to achieve such a hardware architecture, a study of a wide range of block ciphers was undertaken to develop an understanding of the functional requirements of each algorithm. This study led to the development of COBRA, a reconfigurable architecture for the efficient implementation of block ciphers. A detailed discussion of the top level architecture, interconnection scheme, and underlying elements of the architecture will be provided. System configuration and on-the-fly reconfiguration will be analyzed, and from this analysis it will be demonstrated that the COBRA architecture satisfies the requirements for achieving efficient implementation of a wide range of block ciphers that meet the 622 Mbps ATMnetwork encryption throughput requirement.