Read and analyze a client certificate

This article introduces how to read some of the interesting features of a certificate. In the event that you need to analyze the contents of a certificate file, see Tools to Create, View, and Manage Certificates.

Original product version:   Internet Information Services
Original KB number:   216831

Certificate file

After you dump the contents of a certificate, you'll have a file that looks similar to the following:

PKCS7 Message Certificates:
================ Begin Nesting Level 1 ================
X509 Certificate:
Version: 3
Serial Number: 25f51e4e0000115a
Signature Algorithm:
  Algorithm ObjectId: 1.2.840.113549.1.1.4
  Algorithm Parameters:
05 00 ..
Issuer: CN=MS CertSrv Test Group CA, OU=Windows NT, O=Microsoft, L=Redmond, S=WA, C=US
NotBefore: 10/23/1998 3:33 PM
NotAfter: 10/23/1999 3:33 PM
Subject: CN=Name (Signing), OU=IASG, O=Microsoft, L=Redmond,
         S=WA, C=US, E=name@domain.com
Public Key Algorithm:
  Algorithm ObjectId: 1.2.840.113549.1.1.1
  Algorithm Parameters:
05 00 ..
PublicKey: UnusedBits=0
30 48 02 41 00 d4 c1 0e 6f 0b 86 54 b8 9b 08 de 0H.A....o..T....
41 87 b5 e8 62 83 a6 42 a6 63 de 5a 9e cc 17 f6 A...b..B.c.Z....
72 95 52 1f 56 7a 95 ad 33 f0 8e c2 e8 c6 d4 95 r.R.Vz..3.......
0d ce c4 7a 1a f3 10 28 ca 15 46 4e 48 52 8c 89 ...z...(..FNHR..
87 f8 5d 0d 1b 02 03 01 00 01 ..].......
Certificate Extensions: 6
  2.5.29.15: Flags = 0(), Length = 4
     Key Usage
     Digital Signature, Key Encipherment, Data Encipherment, Key Agreement(B8)
 2.5.29.37: Flags = 0(), Length = c
     Enhanced Key Usage
         Client Authentication(1.3.6.1.5.5.7.3.2)

2.5.29.35: Flags = 0(), Length = a9
 Authority Key Identifier
     KeyID=2A58 2026 5B9F CFB1 E328 F42A EA4D F8CA 19CB F3C4
     Certificate Issuer: Directory Address:
             CN=MS CertSrv Test Group CA
             OU=Windows NT
             O=Microsoft
             L=Redmond
             S=WA
             C=US
     Certificate SerialNumber=1113 6100 AA00 2B86 11D2 5EF8 DDA0 99B4

2.5.29.31: Flags = 0(), Length = 91
    CRL Distribution Points
    [1]CRL Distribution Point Distribution Point Name:
    Full Name:
    URL=http://CERTSRV/CertSrv/CertEnroll/MS CertSrv Test Group CA.crl
    [2]CRL Distribution Point Distribution Point Name:
    Full Name:
    URL=file://\\CERTSRV\CertSrv\CertEnroll\MS CertSrv Test Group CA.crl
2.5.29.19: Flags = 0(), Length = 2
    Basic Constraints
        Subject Type=End Entity Path Length Constraint=None
1.3.6.1.5.5.7.1.1: Flags = 0(), Length = 56
    Authority Information Access
        [1]Authority Info Access
    AccessMethod=Certification Authority Issuer(1.3.6.1.5.5.7.48.2)
    Alternative Name:
    URL=http://CERTSRV/CertSrv/CertEnroll/CERTSRV_MS CertSrv Test Group CA.crt
Non-root Certificate

Analyze the certificate

Some of the interesting parts of the certificate include the following:

• PKCS7 Message

  PKCS is a message format for cryptographic messages designed by RSA. For more information, see RSA Security Web site.

• X509 Certificate

  This is the standard format of a certificate.

• Version

  Version 3.0 is the current version.

• Serial Number

  This is a number unique to the entity that issued the certificate.

  Note

  It is possible for two issuers to use the same serial number, but it is rare.

• Signature Algorithm

  The ObjectID or OID is a number used to define an algorithm, application, body part type, character set, external parameter, or message type, among other things. In this example, 1.2.840.113549.1.1.4 means the MD5 hash algorithm. You can get a list of crypto-related OIDs from the WinCrypt.h header file that ships with VC++.

• Issuer

  It's the entity that created the certificate.

• NotBefore/NotAfter

  This is the date range within which the certificate is valid.

• Subject

  Who does this certificate belong to?

• Public Key Algorithm

  1.2.840.113549.1.1.1 means the public key was generated using the RSA algorithm.

• Public Key

  This is the actual data around which this certificate focuses; it's the public key itself.

• Certificate extensions

  These are optional, and only version 3.0 certificates support them. They include Key Usage (what can the public key be used for?), Enhanced Key Usage (similar to the previous), Authority Key Identifier (data used by the issuer to identify this certificate), CRL Distribution Point (where to find information about whether this certificate has been revoked or not).