windows-server-2003/admin/pchealth/helpctr/rc/bdychannel/testsign/faq.txt

General Introduction to Code Signing

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Document Overview
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This guide presents general information about how to use the tools provided
with IE30 to generate and use cryptographic certificates with IE30.  It does 
not attempt to provide an in-depth discussion of public key cryptography, 
X.509 certificates, or certification policy.  See the recommended reading 
list for suggested books and documents that will help you understand those 
and other background issues.

Following this introduction, this guide is divided into the following 
sections:

- Terminology
 
 Describes the terms used in this document that may be new to you.
 
- Procedural Overview
 
 This section gives a brief description of each step of the signing 
procedure and an example of how it would be used by walking through a 
sample session from start to finish.
 
- Required Files List
 
- Recommended Reading

Terminology
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X.509 Certificate - A cryptographic certificate that associates an entity's 
name with its public key.

PKCS 7 "SIGNED DATA" - A widely used convention for containing the data used 
to sign an image or a document, typically including the certificate of the
signer and a statement about the image made by the signer.

WIN_CERTIFICATE - A new Win32 defined data structure that contains either a 
PKCS 7 signed data object or an X.509 Certificate.

Certification Authority (CA) - An entity that is making a statement
(represented by an X.509 Certificate) about the authenticity of some
other certificate.

SPC - Software Publishing Certificate.  A statement that the recipient is an 
approved software vendor, represented as an X.509 certificate.

PE Image - Portable Executable Image, the standard Win32 executable 
format.

Trust provider - A part of the operating system that verifies whether or not 
a given image is trusted based on the certificates it contains.

Procedural Overview
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We will now walk through an example of how to sign an image.  Assume we are
going to sign an image named image.exe.

This procedure is meant to illustrate the steps involved in signing an image 
file.  Since creating a verifiable certificate assumes the existance of a 
fairly complex CA infrastructure, it is not possible to provide all of the 
pieces necessary for a fully trustworthy signature at this time.  In 
particular, there does not exist a "top-level" certifying authority, which 
would ultimately vouch for the integrity of the entire certificate chain.  
Since such a top-level authority is a necessary part of the signing and 
verification operations, the toolkit provided will create a pseudo top-level 
entity when necessary.  This will be called the root authority or root key.

The present tools therefore allow any user of this development release to
authorize themselves as a "Software Publisher" for test purposes and to
sign their code, allowing for extensive testing of the tools and code
used but not actually providing a secure infrastructure. In future releases,
the tools will require software publishers to obtain certificates from
companies whose function is to verify the identity of the publishers,
providing end-users with a high level of assurance about the authenticity
and origin of code that they recieve.

This sample root key will be used to generate an SPC (Software Publishing 
Certificate), which is used to actually sign image files.

[
note: before proceeding, verify that the underlying crypto-api is
functioning by running:
c:>init *   (will generate keys)
c:>api *    (will spew out SUCCESS messages until killed)
]

1) The first step is to run the MakeCert utility.  MakeCert will perform the 
following tasks:

-  Create the end-user's public/private keypair suitable for digital 
signatures, and associate the keypair with a friendly name.
 
-  Associate the new keypair with an X.500 Distinguished Name, and
 
-  Create an X.509 certificate signed by the root key that binds your name to 
the public part of the newly created keypair.

A typical invocation of MakeCert is as follows:

c:\>makecert -u:MyKey -n:CN=MySoftwareCompany Cert.cer

Cert.crt now contains an X.509 certificate that binds your newly created key 
with your name.  This certificate is itself signed by the example root key 
described above.

A public key/private key pair will be generated and assigned the name
specified in the "-u" switch, or if such a key already exists, it will
be re-used.

Note that the name must be of the form "CN=[name-string]", as required by
the ITU x.509 standard.

2) The next step is to wrap the X.509 certificate created in step 1 into a 
PKCS 7 signed-data object.  PKCS 7 objects are commonly used as "carriers" for 
X.509 certificates, because it is possible to put several X.509 certificates 
in a single PKCS 7 object.

In addition to the users's certificate, the root certificate will also be 
inserted into the PKCS 7 object.  This will allow passing around the entire 
certificate chain in a single container.

Do this with the Cert2SPC utility, as follows:

c:\>Cert2SPC Root.cer Cert.cer Cert.spc

Cert.spc now contains the Software Publishing Certificate in the correct 
format.

3) The next step is to use the certificate just created to sign an actual 
image file.  Do this with the SignCode tool.  It takes as input the Cert.spc 
file created in step 2, the name of the key pair created in step 1, and the 
name of the image file to sign.

SignCode will perform the following tasks:

-  Create a cryptographic digest of the passed image file.
 
-  Sign the digest with the passed private key information.
 
-  Extract the X.509 certificates from the passed Cert.spc file.
 
-  Create a new PKCS 7 signed-data object containing the serial number of the 
passed X.509 certificate and the signed digest information.
 
-  Embed the PKCS 7 object into the passed image file.

c:\>SignCode -prog image.exe -spc cert.spc -pvk MyKey

If SignCode is successful, image.exe will have a PKCS7 certificate embedded in 
it.  Verify this by running PeSigMgr.exe on the image:

c:\>PeSigMgr -l image.exe

  Certificate   0 Revision 256 Type    PKCS7

4) Now, check the validity of the image.  Do this with the ChkTrust utility.

c:\>ChkTrust image.exe

ChkTrust performs the following tasks:

-  Extract the PKCS 7 signed data object from the image.
 
-  Extract the X.509 certificates from the PKCS 7 object.
 
-  Compute a new cryptographic checksum of the image file and compare it with 
the signed checksum in the PKCS 7 object.
 
-  If the image checks out, validate that the signer's X.509 certificate 
points back to the root certificate, and that the root key used was correct.

If all this succeeds, the system has verified that the image has not been 
tampered with, and that whoever published this piece of software was 
authorized to do so by the root authority.

List of Required Files
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WINTRUST.DLL
DIGSIG.DLL
OSSAPI.DLL
OSSMEM.DLL
SOEDBER.DLL
MSVCRT20.DLL
MSVCRT40.DLL
MAKECERT.EXE
CERT2SPC.EXE
SIGNCODE.EXE
PESIGMGR.EXE
CHKTRUST.EXE
ROOT.CER
ROOT.PVK