1

Say you want to prove that you received a certain message from someone. This can be difficult because many messaging apps (like facebook messenger) allow the sender to delete messages on the recipient's end.

Of course, you could screenshot the message, but then you still need to prove 2 things:

  1. The time of the message.
  2. The authenticity of your screenshot.

1 is easy, if you upload a hash to public databases as described in this question: Proving creation time/date of a screenshot

2 is a bit more difficult. You'd have to prove somehow that you didn't just forge the screenshot. Note: this is a little different than proving that it was the other person that sent it. This is proving that you received the message from a certain account.

Is there a way establish proof of this?

2

A screenshot is just an image file.

It can be copied without any limitations. Thus having a screenshot does not prove anything.

Everyone can create or edit any file in editor. Having an image file does not prove anything.

Only of you use a messenger that uses digital signature of the sender or uses encryption, you could prove that you received the message. But for this you would need a copy of your message, not the displayed text, but the binary data package that your messenger received from another one. Then:

  • If you present this message ...
  • If this message was encrypted by your public key ...
  • If this message was signed or encrypted by some other sender, not by you, i.e. the sender key used is known to belong to somebody else ...
  • If the message contains a timestamp signed by trusted time server (in case of digital signature such time stamp is a part of signature) ...
  • If you prove that you own your key ...

... Then you can prove that you received that message at that time from that person.

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