How to change E2EE mnemonic?

fun · December 15, 2024, 11:37pm

I recently set up the End-to-End Encryption module on my instance. On first set up, the client desktop app generated a mnemonic secret consisting of 12 random words. I would rather supply my own mnemonic secret. Is this possible?

fun · December 15, 2024, 11:50pm

I’m a little sussed out by the code that generates the mnemonic:

github.com

nextcloud/desktop/blob/788572cfb56ef42abfee8f9eb97700d96e89e615/src/libsync/clientsideencryption.cpp#L252-L275


      
          QByteArray generatePassword(const QString& wordlist, const QByteArray& salt)
          {
              const auto iterationCount = 600000;
              const auto keyStrength = 256;
              const auto keyLength = keyStrength / 8;
          
              QByteArray secretKey(keyLength, '\0');
          
              const auto ret = PKCS5_PBKDF2_HMAC(wordlist.toLocal8Bit().constData(),     // const char *password,
                                                 wordlist.size(),                        // int password length,
                                                 (const unsigned char *)salt.constData(),// const unsigned char *salt,
                                                 salt.size(),                            // int saltlen,
                                                 iterationCount,                         // int iterations,
                                                 EVP_sha1(),                             // digest algorithm
                                                 keyLength,                              // int keylen,
                                                 unsignedData(secretKey));               // unsigned char *out
          
              if (ret != 1) {
                  qCWarning(lcCse()) << "Failed to generate encryption key";
                  // Error out?

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I can’t even tell if it’s actually randomizing anything? PKCS5_PBKDF2_HMAC() is a hash function, right?

Seems weird to describe the E2EE functionality as “production-ready” when users are asked to just take the mnemonic the client randomly generates at face value… Letting the end user introduce their own randomness would eliminate a trust bottleneck, as right now the user simply has to trust that the RNG used here is secure.

system · March 15, 2025, 11:50pm

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