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:
This tool grabs your DKIM DNS TXT record and uses OpenSSL to parse the contained public key to determine its key length.
Update: Nov 6th, 2012 – Return Path is reporting that Google is now “failing anything signed with a 512-bit key or less. A 768-bit key will be accepted for the next few weeks.”
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”.
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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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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