From the course: Symmetric Cryptography Essential Training

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OFB: Output feedback

OFB: Output feedback

From the course: Symmetric Cryptography Essential Training

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OFB: Output feedback

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- [Instructor] The next mode is called output feedback, or OFB, and like cipher feedback, the plain text is combined with the block by block key stream, like a stream cipher. You can see how we've changed the spot where the message is combined with the results of the block cipher. With output feedback, we XOR for the plain text with the key stream and 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. You can see how we've changed the spot where the message is combined with the results of the block cipher. Without output feedback, we XOR for the plain text with the key stream and 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. Conveniently, decryption is exactly the same as encryption, but here we XOR the cipher text with the key stream to produce the plain text. Why might we use this instead of CFB? Unlike…

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