What is the effect of dlls not being signed

Question

On running SigCheck on my Windows box, I noticed quite a few dlls that are unsigned. For eg:

c:\windows\system32\amdocl64.dll:
        Verified:       Unsigned
        File date:      10:47 AM 9/14/2011
        Publisher:      Advanced Micro Devices Inc.
        Description:    AMD Accelerated Parallel Processing OpenCL 1.1 Runtime
        Product:        OpenCL 1.1 AMD-APP-SDK-v2.5 (732.1)
        Version:        2, 5, 732, 1
        File version:   2, 5, 732, 1
c:\windows\system32\amdoclcl64.dll:
        Verified:       Unsigned
        File date:      10:38 AM 9/14/2011
        Publisher:      Advanced Micro Devices Inc.
        Description:    AMD COMPILER OpenCL 1.1 Compiler
        Product:        AMD Compiler Library 1.1 AMD-COMP-LIB-v0.7 (727.0)
        Version:        0, 7, 727, 0
        File version:   0, 7, 727, 0

But I downloaded the executables from the the official AMD website. Why wouldn't AMD sign their dlls? Are their any security issues I need to be worried about, considering the fact that these (among many others, including vendors like HP) are unsigned

Answer 1

The effect is that you are using a driver that has not been authenticated by a third party as coming from the source it purports to be.

Getting drivers signed costs money and takes time to get, If the company is releasing drivers regularly they may not want to spend that money on signing the latest and greatest version every time.

From Microsoft's Driver Signing Requirements for Windows:

Digital signatures allow administrators and end users who are installing Windows-based software to know whether a legitimate publisher has provided the software package.

Generally, if you trust the source you got it from, there should be no concern.