Last week Alice and Bob showed how to cryptographically sign messages so that the recipient can be sure that the message came from the purported sender and hasn’t been forged by a third party. They can only do that if they can securely retrieve the senders public key – which means they need to retrieve it from the actual sender, rather than an impostor, and be sure it’s not...
Alice and Bob can send messages privately via a nosy postman, but how does Bob know that a message he receives is really from Alice, rather than from the postman pretending to be Alice? If they’re using symmetric-key encryption, and Bob is sure that he was talking to Alice when they exchanged keys, then he already knows that the mail is from Alice – as only he and Alice have the keys...
Untrusted Communication Channels This is a story about Alice and Bob. Alice wants to send a private message to Bob, and the only easy way they have to communicate is via postal mail. Unfortunately, Alice is pretty sure that the postman is reading the mail she sends. That makes Alice sad, so she decides to find a way to send messages to Bob without anyone else being able to read them. Symmetric...
A decade or so ago it was fairly rare for cryptography and email technology to intersect – there was S/MIME (which I’ve seen described as having “more implementations than users”) and PGP, which was mostly known for adding inscrutable blocks of text to mail and for some interesting political fallout, but not much else. That’s changing, though. Authentication and...
More than just PGP Cryptography is the science of securing communication from adversaries. In the email world it’s most obvious use is tools like PGP or S/MIME that are used to encrypt a message so that it can only be read by the intended recipient, or to sign a message so that the recipient can be sure of who it came from. There are quite a few other aspects of sending email where a little...
If you use redirection links in the emails you send out, where a click on the link goes to your server – so you can record that someone clicked – before redirecting to the real destination, then you’ve probably already thought about how they can be abused. Redirection links are simple in concept – you include a link that points to your webserver in email that you send out...
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