What happens if you use a password longer then the hash of the KDF? For example in GPG symmetric a password which is 200 characters . On AES-256 ( I don't know the maximum length of the KDF output).

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    $\begingroup$ Could you at least run a spellcheck on your questions? The quality of your questions is deteriorating quickly. $\endgroup$
    – Maarten Bodewes
    Jul 9 '17 at 18:13

The hash functions used as key derivation function take input of arbitrary length (the passphrase) and calculate a fixed-length hash sum used as cipher block (which is 256 bit for AES256, thus the name). Theoretically, you can provide any input size.

$\mathrm{hashfunction}(input) = cipherblock$, while input can have arbitrary length and the hashfunction always returns a 256 bit value.

What sizes actually are reasonable was already discussed in your last question.

  • $\begingroup$ does it have any negative effects ? $\endgroup$ Jul 9 '17 at 19:11
  • $\begingroup$ Very long passphrases have some minor impact on calculation times of the hashsum function (but this is likely to be negligible if you're not debating high-traffic servers), and you might hit unexpected issues when exceeding the passphrase length tested by the software implementations you're relying on. $\endgroup$
    – Jens Erat
    Jul 9 '17 at 19:29

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