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Author: steve

SWAKS: the SMTP Swiss Army Knife

SWAKS is a general purpose testing tool for SMTP. For basic SMTP testing it’s a more convenient, scriptable alternative to running a transaction by hand, but it also lets you test things that are difficult to do manually, such as authentication or TLS encryption. It’s a perl script that installs fairly easily on OS X […]

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I can’t click through if you don’t exist

Recipients can’t click through if you don’t exist A tale of misconfigured DNS wrecking someone’s campaign. I got mail this morning from A Large Computer Supplier, asking me to fill in a survey about them. I had some feedback for them, mostly along the lines of “It’s been two decades since I bought anything other […]

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DMARC and report size limits

I just saw an interesting observation on the dmarc-discuss mailing list. Apparently some of the larger providers who are implementing DMARC for inbound email may not be handling some of the grubbier corners of the spec perfectly. That’s not surprising at all – early adopters tend to deploy code that implements early versions of the […]

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Alice and Bob and PGP Keys

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 […]

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Alice and Bob Sign Messages

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 […]

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Who’s publishing DMARC?

DMARC is a way for a domain owner to say “If you see this domain in a From: header and it’s not been sent straight from us, please don’t deliver the mail”. If a domain is only used for bulk and transactional mail, it can mitigate a subset of phishing attacks without causing too many […]

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Cryptography with Alice and Bob

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 […]

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Cryptography and Email

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 […]

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Make Mail.app work for you

Mark Nottingham (@mnot) posted a good idea to twitter:   Highlight e-mails that your MTA receives with TLS. Make sure to include your mail server’s name in the value (here to the left of what’s shown)     Mail.app has client support for mail routing rules. Out of the box all they’re configured to do is […]

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Who didn’t invent email?

Who didn’t invent email? Shiva Ayyadurai. He’s not the only one – I didn’t invent email either, nor did Abraham Lincoln, Boadicea or Tim Berners-Lee. So why mention Shiva? He claims that in 1978 when he was 14, he took some courses in programming. His mum worked for the University of Medicine and Dentistry of […]

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