Understanding Cryptography by Christof Paar and Jan Pelzl - Chapter 5 Solutions - Ex5.6

- 1 min

Exercise 5.6

Propose an OFB mode scheme which encrypts one byte of plaintext at a time, e.g., for encrypting key strokes from a remote keyboard. The block cipher used is AES. Perform one block cipher operation for every new plaintext byte. Draw a block diagram of your scheme and pay particular attention to the bit lengths used in your diagram (cf. the descripton of a byte mode at the end of Sect. 5.1.4).


I haven’t yet verified this solution independently. If you spot any mistakes, please leave a comment in the Disqus box at the bottom of the page.

Below is an OFB scheme which matches the requirements:

OFB Scheme

Note: In places where 128 bits are truncated to 8 bits, this is done by taking the first 8 bits.

Thomas Busby

Thomas Busby

I write about computing stuff

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