Irrespective of the raw speed figures, the three studies indicate that for some processors, there may be a significant difference in an algorithm's speed for encryption and decryption when comparing interleaved and feedback modes.
RC6 provides average to high-end performance for encryption and decryption, and average performance for key setup.
Rijndael provides consistently high-end performance for encryption, decryption and key setup, although performance decreases for the 192 bit and 256 bit key sizes.
MARS provides average performance for encryption, decryption and key setup.
In particular, it is possible to reconfigure an FPGA to switch from one algorithm to another algorithm, or from encryption to decryption or key setup.
Subkey computation can be implemented within the FPGA, in which case the array could be configured for subkey computation, and then reconfigured for encryption or decryption.
Cipher Block Chaining, Cipher Feedback, and Output Feedback), the encryption or decryption of the next block cannot begin until the present block has finished.
If an algorithm has homogeneous rounds, the simplest implementation of encryption or decryption in hardware is to implement one round in combinational logic.
Another possibility is to perform subkey computation in hardware prior to encryption or decryption, and store the subkeys in registers or RAM.
Both encryption and decryption were implemented in units co-existing simultaneously within the FPGA.
This path of operations, shared by encryption and decryption, determines the minimum clock period of the system.
In addition, if the amount of RAM is constrained, then decryption will be very slow.
For example, if encryption and decryption were implemented simultaneously, Serpent and Rijndael would be penalized because of the lack of resource sharing, and Twofish would be rewarded for its independent subkey computation.
The results are given for the encryption of a single block with a 128 bit key, exce pt that the author considered decryption as well as encryption for Rijndael (RIJN(d)).
Both encryption and decryption are at least twice as fast as any other finalist.