If you ever receive a Delta Chat invite (URL or
QR code) purporting to be from me, check that the fingerprint in it is
mine: 65F37749BA1552C5553B1227E90F38490FEE4635.
With Delta Chat, there are no user directories: the only way to contact someone is by providing them your Delta Chat profile in the form of a URL, which can be presented through a QR code.
From now on, every time I write “the QR code”, you can read that as “the URL or its QR code”.
Providing your QR can be done face-to-face (you display your QR code, the other person scans it, or the reverse), or through any channel of your choice: another messaging system, mail, paper…
Beware however: said QR code allows anyone to contact you; it’s up to you to verify if that person is who they say they are. Face to face, that can be easy. Otherwise, less.
But there is a way to check, or more exactly, there is a way to allow others to verify that a QR code indeed comes from your profile: you just need to publish, through another, secure, channel (such as your website or your profiles in other social networks), your profile’s fingerprint.
You can find this fingerprint, which consists of forty digits and upper caps letters, at the start of the l’URL in your profile’s QR code.
Technically, this fingerprint is that of the PGP key associated with the profile. Don’t worry if that means nothing to you.
For instance, “my” URL starts with:
https://i.delta.chat/#65F37749BA1552C5553B1227E90F38490FEE4635&v=...
Thus my fingerprint is 65F37749BA1552C5553B1227E90F38490FEE4635.
This fingerprint is unique for a given Delta Chat profile; even if you reset your QR code, the new QR code will bear the same fingerprint.
So, if you receive an invite from me, and even if we never communicated through Delta Chat before, you can verify it is genuine by checking that its fingerprint matches mine!