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I just received an email that seemingly comes from Microsoft (invites@microsoft.com). Apart from asking Microsoft, is there a way to properly authenticate an email's origin with public key etc? (Especially from a company like MS or google?)

I just finished an Crypto intro course and am just curious about this in general.

6

Yes, but all the reliable methods are optional:

  • PGP signing (also depends on you already having a large PGP network or directly having accepted the real senders public key)

  • x509 signing (S/MIME) - which few people use, despite relatively painless setup on the signing side

  • DMARC - which probably isn't supported in your mail user agent but is gaining wide adoption in MTAs.

  • Sender Policy Framework - again is probably ignored by your user agent but commonly implemented in MTAs - Not as robust as the methods above which use cryptographic signatures.

A further issue with all of these technologies is that they are designed as means for computers to validate the identity of other computers rather than as a way of proving to human beings that an email is genuine.

  • Thanks for the answer! I was under the impression that common email protocol has some "bread crumbs" that lead back to the where it came from with some crypto magic. I will look into the DMARC, sounds interesting. – pip Nov 19 '17 at 3:23
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    You can see the chain of "received-from" headers - but this is trivial to forge – symcbean Nov 19 '17 at 18:16

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