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"modify it" - looks like a new email to me. It's going to have a different secure digest. You can argue semantics here - but the main difference is: YOU can
by brongondwana 9y ago
"modify it" - looks like a new email to me. It's going to have a different secure digest. You can argue semantics here - but the main difference is:
YOU can modify the messages in your Inbox.
THE SENDER can not. Unless they have write access to your mailbox and can copy things out in a client, edit them, and write them back.
- mehrdadn 9y agoRegarding the "the sender" thing -- see my update above; sorry I was busy editing my comment before you posted this. Regarding the secure message digest: if that's your claim, maybe clarify that "[DKIM-]signed messages are tamper-proof"? Because not all email messages are signed. Also, I think you can still upload messages with broken signatures (not sure?) in most mailboxes, and the user won't necessarily know either (who verifies DKIM signatures manually?)... but I'd have to double-check this.
- brongondwana 9y agoYeah, probably true - I did mention our non-standard DIGEST.SHA1 (I'd like to change that algorithm at some point, though the risks are kind of overblown, particularly since we inject some randomness in the SESSIONID field that's part of the Received header added on every delivery) That said, if you tried to claim that a message was from somebody and used a tampered version, then checking the DKIM signature is something I expect would be done as part of the forensic analysis, as would checking the mail server logs. At least on our servers, you'd be able to tell from the logs that the digest changed when the new copy was uploaded - assuming you claimed something about downloading it and moving it to a new folder with your client.