How to Read and Analyze a Client Certificate

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Summary

This article explains 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, please see the following article in the Microsoft Knowledge Base:
216830 How to View the Contents of a Certificate

More Information

After you dump the contents of a certificate, you will 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
Note: This certificate was modified in order to fit in this window.

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, visit the following 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
Is 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 is 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 Points (where to find information about whether this certificate has been revoked or not).

For more information, see the following articles in the Microsoft Knowledge Base::
216830 How to View the Contents of a Certificate

216829 How to Write a Client Authentication Certificate to a File in IIS 4.0
Propriétés

ID d'article : 216831 - Dernière mise à jour : 15 déc. 2008 - Révision : 1

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