title: Kext with invalid signature can load on one machine, but not the other. Why?
body: <p>I have an iMac and a Macbook Pro. I updated both to Yosemite beta (the public one).
  But my audio interface Focusrite Saffire 24 DSP (Firewire) works properly in the iMac, but not on the Macbook Pro.</p>
  
  <p>When installing the Saffire, there is a Saffire.kext.
  When connecting it to the iMac, this kext loads fine, nothing unusual.
  This kext does NOT load when connecting it to the Macbook Pro.
  I tried loading it manually, and I get an error message saying that it can't be loaded since the kext has an invalid signature.</p>
  
  <p>Now, I checked the signature on both computers, and they both say that the signature is invalid. But it loads fine on the iMac, even though the signature is invalid.</p>
  
  <p>Why is that? What am I not understanding?</p>
  
  <p>Here is some console output if that helps:</p>
  
  <pre><code>Mattiass-MacBook-Pro:Extensions mono$ codesign -dvvv Saffire.kext/
  Executable=/System/Library/Extensions/Saffire.kext/Contents/MacOS/Saffire
  Identifier=tc.tctechnologies.driver.Saffire
  Format=bundle with Mach-O universal (i386 x86_64)
  CodeDirectory v=20100 size=161 flags=0x0(none) hashes=1+3 location=embedded
  Hash type=sha1 size=20
  CDHash=ebc9c42dbea4f51770ff62d7de12552ae82a1fbc
  Signature size=4240
  Authority=Developer ID Application: TC Applied Technologies
  Authority=Developer ID Certification Authority
  Authority=Apple Root CA
  Signed Time=13 Mar 2014 02:58:23
  Info.plist entries=19
  TeamIdentifier=not set
  Sealed Resources version=1 rules=4 files=0
  Internal requirements count=1 size=180
  
  Mattiass-MacBook-Pro:Extensions mono$ codesign --verify -vvvv Saffire.kext/
  Saffire.kext/: invalid signature (code or signature have been modified)
  In architecture: x86_64
  </code></pre>
  
  <p>(The Saffire is connected to a Belkin Thunderbolt Dock, which is connected to the MBP, if that matters.)</p>
  
  <p><strong>UPDATE:</strong></p>
  
  <p>Here is the error message in the log.</p>
  
  <pre><code>28/07/14 00:51:33,693 com.apple.kextd[19]: ERROR: invalid signature for tc.tctechnologies.driver.Saffire, will not load
  </code></pre>
  
  <p><strong>UPDATE 2:</strong></p>
  
  <p>I got it to work in the MBP as well.
  I found this post: <a href="http://www.cindori.org/enabling-trim-on-os-x-yosemite/">http://www.cindori.org/enabling-trim-on-os-x-yosemite/</a>
  which lead me to try out this command: </p>
  
  <pre><code>sudo nvram boot-args="kext-dev-mode=1"
  </code></pre>
  
  <p>After a reboot, everything was up and running again.</p>
  
  <p>My question remains unanswered though, why did it work on the iMac but not the MBP?</p>