From the course: Symmetric Cryptography Essential Training

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CTR: Counter mode

CTR: Counter mode

From the course: Symmetric Cryptography Essential Training

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CTR: Counter mode

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- [Instructor] The final mode I'll be covering is counter mode, sometimes referred to as CTR mode. This is another mode that looks like a stream cipher, but here, each block encrypts a unique counter value that's combined with an initialization vector. The output of this encryption is XOR-ed with the plaintext block to create the ciphertext block. Here, you see that the decryption is the same as the encryption, with the ciphertext blocks and the plain text blocks just reversed. Like output feedback, ciphertext isn't actually involved in producing later blocks. And also like output feedback, error correction that's applied to the plaintext will still work properly. Unlike output feedback, though, we can do both encryption and decryption in parallel. That allows us to massively speed up encryption and to have access to the plaintext at any position in the ciphertext. One important and hopefully obvious thing to note is that the counter value in integer must be represented consistently…

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