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I know this is theoretically bad practice, but please bear with me…

Assuming following spec:

  • Salt and IV are randomly generated using cryptographically-secure RNG.

  • Argon2 is used as KDF so key_1=Argon2(shared_salt, passphrase_1) and key_2=Argon2(shared_salt, passphrase_2).

  • Both passphrases are not vulnerable to dictionary attacks and the like.

  • Shared salt and IV are only (re-)used once in the context of singular concatenated encrypted paper backup.

Encrypted paper backup = concat(shared_salt, shared_iv, AES-256-CBC(shared_iv, key_1, "some text"), AES-256-CBC(shared_iv, key_2, "some other text"))

According to https://crypto.stackexchange.com/a/10511/83430, it appears above spec should hold up to pretty sophisticated attacks (if vulnerable at all).

See proof of concept.

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  • $\begingroup$ This seems to be the same question you posted before, except you're now mentioning that it's for paper backups. As you were talking about VeraCrypt before, please can you clarify what that means and how it's related to plausible deniability. I really don't understand what you're trying to achieve. $\endgroup$
    – samuel-lucas6
    Commented Sep 7, 2022 at 20:01
  • $\begingroup$ Thanks for helping out @samuel-lucas6. Researching encryption schemes that could yield similar results to VeraCrypt hidden volumes, yet with as many “hidden” secrets as one needs and in a form that can be printed using QR codes. $\endgroup$
    – sunknudsen
    Commented Sep 7, 2022 at 20:10
  • $\begingroup$ Forensic Analysis breaks the plausible deniability of Veracrypt linked in this answer... $\endgroup$
    – kelalaka
    Commented Sep 7, 2022 at 23:04
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    $\begingroup$ When we talk about IV reuse we talk about it in the context of a specific key. If you are using your IV for mathematically unrelated keys then it is not really reuse. $\endgroup$
    – Maarten Bodewes ♦
    Commented Sep 8, 2022 at 12:01
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    $\begingroup$ @sunknudsen If you don't know where each secret starts, how can it be decrypted? Did you look at the PURBs paper I linked before? $\endgroup$
    – samuel-lucas6
    Commented Sep 8, 2022 at 12:41

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