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AEAD Packet Builder

Assemble key, nonce, associated data, ciphertext, and tag, then see why nonce reuse breaks the whole design.

flowKeyK = 256-bit secretNoncenot allocated yetAADheader pendingPlaintextinvoice_total=€18420keystream XORCiphertextnot produced yetTagnoneverify firstnonce reuseSymmetric crypto starts with shared secret material, not with a public key exchange at the message layer.[key only in memory]
Step 1 / 7A shared symmetric key already exists

Both sides start with the same secret key. That key is the root of the whole encrypted channel or object format.

Packet view: [key only in memory]

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