Verifying a DKIM TXT Record and Key Length

November 3, 2012

After reading the Wired story last week about Zachary Harris discovering a widespread vulnerability related to the use of weak cryptographic DKIM keys (less than 1024 bits) by companies like Google, eBay, Yahoo, Twitter and PayPal, and the subsequent CERT warning (VU#268267), I decided to write a quick tool to check DKIM TXT records and determine their key length:

DKIM Key Checker

This tool grabs your DKIM DNS TXT record and uses OpenSSL to parse the contained public key to determine its key length.

Github SSH Public Key Fingerprint Checking

March 7, 2012

A security vulnerability was discovered at GitHub this week that made it possible for an attacker to add new SSH keys to arbitrary GitHub user accounts. Although there was no known malicious activity using this exploit, they are taking the responsible step to email all their users that have SSH keys associated with their account to verify and approve them before they can be used to clone/pull/push repositories over SSH.

The GitHub audit page looks like this:

Here’s a quick reminder of how to get the fingerprint of your SSH public key using the ‘ssh-keygen’ command. Use the name of your local public key file that you want to check.

ssh-keygen -lf id_protodave_github.pub

The resulting fingerprint will look like:

2048 b5:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:2f  protodave@github (RSA)

If this fingerprint of the local trusted copy of your SSH public key matches the one GitHub shows you, then you are safe to click “Approve”.

Eclipse, EGit, github, jsch and AES-128 encrypted private keys

January 25, 2011

Here’s a tip if you are having trouble connecting to github using Eclipse/Egit with a recently generated SSH key pair…

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Javascript Word Wrapping

January 18, 2011

I recently needed to do some manual word wrapping (and possibly hyphenation) of strings in JavaScript and found some interesting code projects:

Checking your DKIM DNS record

January 6, 2011

Update Nov 2012:

Due to the recently released vulnerability related to the use of weak cryptographic DKIM keys, I wrote a tool to check DKIM records and determine their public key length: DKIM Key Checker

 

DKIM For The Masses

Google announced today they have added the ability for Google Apps customers to sign outbound email using the DKIM (DomainKeys Identified Mail) standard.

You can set it up for your own Google Apps domain (if you are the domain admin) using these instructions.

It’s a simple process but the trickiest part can be creating the DNS TXT record (which contains your DKIM public key), depending on how you manage your DNS. If you are serving DNS directly via your registrar, Google has some specific instructions for popular domain hosts.

Checking your work

Here’s a quick tip how you can check to make sure you created the record properly and it is being served…

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