New answers tagged nonce
AES-CTR is very appropriate. Since a credit card number is 16 characters long, it can be encrypted using a single 128-bit block without any encoding. You will only need 1 block, and hence not require a block counter, just the nonce. Depending on the amount of card numbers being stored, you would only need to store a portion of the full nonce. A 32-bit ...
The standard approach is to have the sender pick his nonce (either randomly, or as a counter), and send it with the packet. The decryptor then knows what nonce to use to decrypt, because it's right there. Because nonces aren't assumed to be secret, this works.
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