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Definition: counter mode

In cryptography, a sophisticated mode of operation. Counter mode uses an arbitrary number (the counter) that changes with each block of text encrypted. The counter is encrypted with the cipher, and the result is XOR'd into ciphertext. Since the counter changes for each block, the problem of repeating ciphertext that results from the electronic code book (ECB) method is avoided. See mode of operation, block cipher, XOR and AES-CCMP.