From the course: Symmetric Cryptography Essential Training
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OFB: Output feedback
From the course: Symmetric Cryptography Essential Training
OFB: Output feedback
- [Instructor] Now, we'll cover a mode called Output Feedback, or OFB, and like Cipher Feedback, the plain text is combined with the key stream like a stream cipher. You can see how we've changed exactly where the message is combined with the results of the block cipher. With Output Feedback, we explore the plain text with the key stream and we use that result as the cipher text. With Cipher Feedback, we use that result as both the cipher text and as the input to the next block. So, unlike Cipher Feedback, the cipher text is not used with subsequent blocks as we saw in the diagram, but OFB allows for error correcting codes to be applied to the plain text and then they still work with the cipher text, but with Output Feedback, we can't encrypt or decrypt in parallel like we did with CFB. One of the nice features about Output Feedback is that it's easy to precalculate the key stream. It's also more error tolerant than Cipher Feedback. A 1-bit cipher text error only results in a 1-bit…
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