# Tag Info

3

I've seen this a few times, so I want to point out something that is a general misconception. People often think that for key derivation, it's really important that I don't get repetition, since that is a break. However, this is actually very not true, and the opposite is true. I will explain. The "ideal situation" is to just choose keys, truly at ...

1

The present answer is made for the sake of answering an answerable question, and the cases where collisions actually matter: like, they are observed and we want to rule out it's by chance; or some authority specified that each smurf must have a unique key, and lack of a convincing argument for that separates the rubber stamp from the paperwork. See Yehuda ...

0

Do secret keys get expired, or just the public key gets expired? The private key does not expire. A public key expires, but only in the sense that the certificate(s) part of it expires. The public key value does not change when a renewed public key is issued. Do I have to back up the master sec key each time I renew it? No. Also, only the public key (or ...

0

From my understanding, I only need one key for CHACHA20 or AES-256-GCM. Is it a good idea if I only generate one key by HKDF? In one direction yes, as the MAC and encryption part only requires on e key for ChaCha20/Poly1305 and AES-GCM. If you need multiple key parts you can either increase output size and split the result, or you can call HKDF twice using ...

5

You don't get empty output in AES, too. AES is a permutation and will always return a plaintext, correct or not depending on the key. If I take the SHA3_512 of the Argon2ID-ed password and include it with the ciphertext, is the ciphertext now vulnerable to attacks? One needs to find a pre-image to the key, and normally the cost of this is around $2^{512}$ ...

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