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If your IV is predictable this is as (in)secure as assuming that you have a zero vector IV. And a zero vector IV allows you to perform a so-called Adaptive Chosen Plaintext Attack (ACPA). Why? Assume that you have a encryption mechanism that works in CBC mode. This means, that on the first iteration the $IV$ is XORed with your input message (which is ...

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Yes, it's secure. It is somewhat overkill, however, since you could stop replay attacks by using either: a persistent counter as IV, or a random nonce, and including a timestamp in the message. The AEAD must authenticate the IV (and GCM certainly does), so either would work without requiring any extra round-trips. You can just use the IV in the initial ...

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Using Diffie-Hellman key agreement for generating a nonce should be safe as long as both key pairs are ephemeral, i.e. generated for each run of the key agreement protocol. Otherwise a man-in-the-middle can fool one of the parties in generating the same nonce over and over again. Ephemeral Diffie-Hellman is however overkill for generating a nonce, as the ...

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This algorithm is vulnerable to a Man in the middle. From Wikipedia: In the original description, the Diffie–Hellman exchange by itself does not provide authentication of the communicating parties and is thus vulnerable to a man-in-the-middle attack. Mallory may establish two distinct key exchanges, one with Alice and the other with Bob, effectively ...

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AES is a block cipher which actually only "maps" (encrypt) a 128 bit block (plainblock) to a 128 bit block (cipherblock) and vice versa. This "mapping" is key dependent. To encrypt some data you normally apply an encryption mode like CBC, CTR, GCM etc. using e.g. AES as block cipher within this mode. These modes normally require an IV or Nonce. So, not ...

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