OFB-DES, OFB-AES128, OFB-AES192, and OFB-AES256 modes are supported in this implementation.
Attention
The bit-width of the interfaces provided is shown below:
| plaintext | ciphertext | cipherkey | IV | |
| OFB-DES | 64 | 64 | 64 | 64 |
| OFB-AES128 | 128 | 128 | 128 | 128 |
| OFB-AES192 | 128 | 128 | 192 | 128 |
| OFB-AES256 | 128 | 128 | 256 | 128 |
The algorithm flow chart is shown as follows:
As seen from the chart, both encryption and decryption part of OFB mode has dependencies, so the input block of each iteration (except for iteration 0) needs a feedback data from its last iteration. Thus, the initiation interval (II) of OFB mode cannot achieve an II = 1.