From the course: Symmetric Cryptography Essential Training
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CFB: Cipher feedback
From the course: Symmetric Cryptography Essential Training
CFB: Cipher feedback
- [Instructor] Cipher Feedback or CFB mode converts a block cipher into something that looks very much like a stream cipher. Rather than encrypting the plaintext directly, the plaintext is combined with the key stream, just like a stream cipher would. I think that CFB looks a bit like cipher block chaining run backwards. Block ciphers in CFB mode turn into a self-synchronizing stream cipher, and what this means is corrupted ciphertext, even a single byte, ends up corrupting the entire plaintext block, but doesn't affect any later blocks. And the reason is is that the results of decrypting the previous ciphertext blocks don't get used to decrypt later ciphertext blocks. Like CPC mode, we can't encrypt in parallel, but we can decrypt multiple blocks at the same time. This gives us random access to decrypt plaintext blocks as we need them. Here's the process for decryption. The block cipher encrypts the initialization vector with the key and the output of that is then exored with the…
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