aes256cbc: Use no padding instead of zero padding#210
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robin-nitrokey merged 1 commit intomainfrom May 15, 2025
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Reviewed applications:
- Opcard OK (we check length and reject non multiple of 16 bytes)
- PIV: AES only ever encrypts/decrypts 16 bytes (and check the length)
- FIDO
- Secrets (no AES)
- Webcrypt (AES is used without checking length, here it's an issue, we can ignore for now because not even included in the test firmware).
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There is actually one case in fido-authenticator where zero-padding is performed: the encrypted PIN when setting a new PIN. I’ll prepare a PR with this change. |
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Nevermind, fido-authenticator already strips the padding (though this was probably not necessary with the current implementation): Also, the full test suite succeeds even with this PR. |
sosthene-nitrokey
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May 15, 2025
Defaulting to zero padding can be problematic. Using no padding leaves it up to the application to handle the padding correctly according to the use case. Fixes: #209
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Defaulting to zero padding can be problematic. Using no padding leaves it up to the application to handle the padding correctly according to the use case.
Fixes: #209
To do: Review all applications and backends to ensure that only full blocks are used with AES-256.