AES-CTR Mode

CTR mode turns a block cipher into a stream cipher by encrypting a nonce and counter to produce a keystream, then XORing with plaintext.

Function signature

func CryptCTR(key [16]byte, nonce [8]byte, counter uint64, data []byte) []byte

Behavior

• Construct the counter block as nonce || counter (8 bytes each, big-endian).
• For each 16-byte block, encrypt the counter block with AES.
• XOR the keystream with data; increment the counter for the next block.
• Encryption and decryption are identical.

Notes

• AES block encryption is provided.
• Reusing the same (nonce, counter) pair with the same key is catastrophic.