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Category: Technical

EFAIL PGP / S/MIME “flaw” 🚂

There’s going to be a lot of hype today about something the security researchers who found it are calling “EFAIL”. Interviews, commemorative T-Shirts, press tours, hype. The technical details are interesting, but the un-hyped end-user advice would probably be “If you’re using a mail client that’s got bugs in it’s MIME handling, and you’ve configured it […]

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Dodgy PDF handling at Gmail

We sent out some W-9s this week. For non-Americans and those lucky enough not to have to deal with IRS paperwork those are tax forms. They’re simple single page forms with the company name, address and tax ID numbers on them. Because this is the 21st Century we don’t fill them in with typewriters and […]

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Meltdown & Spectre, Oh My

If you follow any infosec sources you’ve probably already heard a lot about Meltdown and Spectre, Kaiser and KPTI. If not, you’ve probably seen headlines like Major flaw in millions of Intel chips revealed or Intel sells off for a second day as massive security exploit shakes the stock. What is it? These are all about a […]

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Authentication is about Identity, not Virtue

I just got some mail claiming to be from “Bank of America <secure@bofasecure.com>”. It passes SPF: Received-SPF: Pass (sender SPF authorized) identity=mailfrom; client-ip=185.235.176.160; helo=bofasecure.com; It passes DKIM: Authentication-Results: mx.wordtothewise.com (amavisd-new); dkim=pass (1024-bit key) header.d=bofasecure.com The visible RFC 822 From address is strictly aligned with both the SPF domain and the DKIM domain. So if they’d published […]

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Organizational Domain

We often want to know whether two hostnames are controlled by the same person, or not. One case for that is cookie privacy in web browsers. We want pages at www.blighty.com and images.blighty.com and blighty.com to all be able to set and read cookies for each other – so a user only needs to log […]

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Mandatory TLS is coming

Well, not exactly mandatory but Chrome will start labeling any text or email form field on a non-TLS page as “NOT SECURE”. Chrome 62 will be released as stable some time around October 24th. If you want to avoid the customer support overhead then, regardless of whether any of the information on a form is […]

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Local-part Semantics

An email address has two main parts. The local-part is the bit before the @-sign and the domain is the bit after it. Loosely, the domain part tells SMTP how to get an email to the destination mailserver while the local part tells that server whose mailbox to put it in. I’m just looking at the local part today, the […]

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TLS certificates and CAA records

Transport Layer Security (TLS) is what gives you the little padlock in your browser bar. Some people still call it SSL, but TLS has been around for 18 years –  it’s time to move on. TLS provides two things. One is encryption of traffic as it goes across the wire, the other is a cryptographic […]

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Are they using DKIM?

It’s easy to tell if a domain is using SPF – look up the TXT record for the domain and see if any of them begin with “v=spf1”. If one does, they’re using SPF. If none do, they’re not. (If more than one does? They’re publishing invalid SPF.) AOL are publishing SPF. Geocities aren’t. For DKIM […]

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Protocol-relative URLs in email

When you link to an external resource – an image, a javascript file, some css style – from a web page you do so with a URL, usually something like “https://example.com/blahblah.css” or “http://example.com/blahblah.css”. The world is beginning to go all https, all the time, but until recently good practice was to make a web page available […]

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