"With block cipher, each plaintext block is XOR-ed with the previous ciphertext block and then encrypted, this is known as block chaining. This prevents identical blocks of plaintext from producing the same ciphertext each time they are encrypted"

What happens inside the clause of the "XOR" statement, to make two equal plain text blocks encode into two different cipher text blocks?

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    $\begingroup$ What do you mean by "xor inBlock chaining"? I can't understand what you mean by "standard action to take... to make..." either. Please edit your question to elaborate on what you are asking. Give us some context and background, define all terms (e.g., inBlock), perhaps tell us your motivation -- all of that might help to understand what you're asking. $\endgroup$ – D.W. Jan 15 '20 at 5:47
  • $\begingroup$ I added context and reworded the question $\endgroup$ – Dylan Jan 15 '20 at 8:48
  • $\begingroup$ It appears you are quoting from somewhere. Please provide a full reference to the original source of all quoted material. This may help us get you a better answer, and helps others with a similar question find this page via search. $\endgroup$ – D.W. Jan 15 '20 at 9:36

Say you have blocks ABCDEA that you want to encrypt. If you do this naively, then the first and second A produce the same encrypted result, and an attacker would know that your first and last block are the same.

Instead you encrypt to A’B’C’ etc. by encrypting A -> A’, A’ XOR B ->B’, B’ XOR C -> C’, ..., E’ XOR A -> F’. It looks like you are encrypting random data, nothing an attacker can do.

The identical plain text blocks are XOR-ed with different previously encrypted blocks, that what’s making them different.

  • $\begingroup$ Is there more meaning to the term "XOR-ed" than just checking they're different? If not then how does a check change the cypher text to a non-identical form. $\endgroup$ – Dylan Jan 19 '20 at 6:46

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