7.4.4.1 Operating Modes
The TDES supports the following operating modes:
- ECB—Electronic Code Book
- CBC—Cipher Block Chaining
- OFB—Output Feedback
- CFB—Cipher Feedback
- CFB8 (CFB where the length of the data segment is 8 bits)
- CFB16 (CFB where the length of the data segment is 16 bits)
- CFB32 (CFB where the length of the data segment is 32 bits)
- CFB64 (CFB where the length of the data segment is 64 bits)
The data pre-processing, post-processing and data chaining for each mode are automatically performed. Refer to the FIPS Publication 81 for more complete information.
These modes are selected by setting TDES_MR.OPMOD.
In CFB mode, four data sizes are possible (8, 16, 32 and 64 bits), configurable in TDES_MR.CFBS (see TDES Mode Register).