Block cipher modes of operationSorry for my ignorance but what are the Encryption "Modes" used for ?
"In cryptography, a block cipher operates on blocks of fixed length, often 64 or 128 bits." Modes decide how one block will affect another during encryption. This is for instance necessary for identical blocks of plaintext to be encrypted to different blocks of ciphertext. More advanced uses can certainly be dug up, too.

HTH
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