-VAMSI SRI HARSHA VIDALA

X.509 certificate management in .NET

Introduction

A public key certificate is digitally signed document that is commonly used for authentication and secure exchange of information on open networks.

A certificate securely binds a public key to the entity that holds the corresponding private key.

Certificates are digitally signed by the issuing certification authority (CA). They create a trust relationship between two unknown entities.

Overview of X.509 certificates

Entities involved in X.509 certificate management.

o Subjects and End Entities.

o Certification Authority(CA).

o Registration Authority(RA).

Certificate Management Operations

End Entity

RA

CA-2

CA

Cert. publish

Cert. publish

Cert. publish

Cert. “USERS”

Cert. Mgmt Entities

“Out-of-Band” loading

“Out-of-Band” publication

Cross-certification.Cross- Certificate Update.

Initial Registration/ Certification.Key Pair recovery.Key Pair Update.Certificate Update.Revocation Request.

Certificate Management Operations

CA establishment.

End entity initialization.

Certification: Initial registration/Certification. Key pair Update. Certificate Update. CA Key pair update. Cross-certification Request. Cross-certificate Update.

Operations(contd.)

Certificate/CRL discovery operations. Certificate Publication CRL Publication

Recovery operations Key-pair recovery

PSE operations

Implementation in ASP.NET

Formats for X.509 Certificate

Format Extension

DER Encoded Binary X.509 cer

Base64 Encoded X.509 cer

PKCS#7 / Cryptographic Message Syntax Standard

p7b

PKCS#12 / Personal Information Exchange pfx

Note:The most widely accepted format for certificates is

defined by the ITU-T X.509 version 3 international standards.

The certificates are encoded using OSI ASN.1 DER.

Primary Fields in X.509 certificate

Field Meaning

Version Which version of X.509

Serial number This number plus the CA’s name uniquely identifies the certificate

Signature algorithm The algorithm used to sign certificate

Issuer X.500 name of CA

Validity Period The starting and ending period

Subject name The entity whose key being certified

Public Key The subject’s pubic key and ID of algorithm using it

.NET Certificate Management Tools

Application Usage

Makecert Generate a X.509 certificate

Certmgr Assembles certificates into CTL (certificate trust list) and can also be used for revoking lists (CRLs)

Chktrust Verifies the validity of a file signed with an X.509 certificate

Cert2spc Creates a Software Publisher's Certificate (SPC) from one or more X.509 certificates

pvk2pfx Convert the certificate .cer and .pvk to .pfx

WseCertificate2 X.509 Certificate tool to displays details about X.509 certificates.

Using X.509 Certificates in .NET application

1. Create and manage X.509 Certificate

2. Sign a SOAP Message Using an X.509 Certificate

3. Verify Digital Signatures of SOAP Messages Signed by an X.509 Certificate

STEP I

Create and manage

X.509 Certificate

Obtain X.509 Certificate

Purchase a certificate from a certificate authority, such as VeriSign, Inc

Set up our own certificate service and have a certificate authority sign the certificates

Set up our own certificate service and do not have the certificates signed

Note:Whichever approach we take, the recipient of the SOAP request containing the X.509 certificate must trust the X.509 certificate.

Creating and configuring X.509 Certificate

Create certificate using makecert.execmd>makecert -n "CN=TempCA" -r -sv TempCA.pvk TempCA.cer

Import the created certificate using MMC in to the certificate storeImport the certificate TempCA.cer using MMC in to "Trusted Root Certificate Authorities" folder

Export the created certificate to outside world by creating and distributing pfx file using pvk2pfx toolcmd>pvk2pfx -pvk TempCA.pvk -spc TempCA.cer

Define access permission for X.509 certificate cmd>winhttpcertcfg -g -c LOCAL_MACHINE\MY -s TempCA -a ASPNET

Make certificates accessible to application

Specify the certificate store that application uses to obtain X.509 certificates <configuration>

<microsoft.web.services2> <security>

<x509 storeLocation="CurrentUser" />

</security> </microsoft.web.services2>

</configuration>

Specify the account under which application is running read access to the file containing the private key associated with the X.509 certificate.<processModel enable="true|false"  userName="username"  password="password" />

Default accessibility for certificates

X.509 certificate use Private key

Digitally signing an outbound SOAP Yes

Verifying the signature of an inbound SOAP No

Encrypting an outbound SOAP message No

Decrypting an inbound SOAP message Yes

X.509 certificate use Client Application Web service (.ASMX)

Signing or encrypting an outgoing SOAP message.

Local Computer's Personal Store

Local Computer's Personal Store

Verifying the signature of an incoming SOAP message

SOAP message SOAP message

Decrypting an inbound SOAP message

Local Computer's Personal Store

Local Computer's Personal Store

Default Locations of certificate store:

Usage of private key:

STEP II

Sign a SOAP Message

Using an X.509 Certificate

Config file settings for using X.509 certificates

<policyDocument xmlns="http://schemas.microsoft.com/wse/2003/06/Policy">

<mappings xmlns:wse="http://schemas.microsoft.com/wse/2003/06/Policy"> <endpoint uri="http://www.cohowinery.com/SaleWidgets.asmx"> <defaultOperation> <request policy="#policy-c0a22319-6b89-49ff-9b82-bdbac5f04618" /> <response policy="#policy-c0a22319-6b89-49ff-9b82-bdbac5f04618" /> <fault policy="#policy-c0a22319-6b89-49ff-9b82-bdbac5f04618" /> </defaultOperation> </endpoint> </mappings> <policies … </policies></policyDocument>

Config file settings for using X.509 certificates

<policies xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-

1.0.xsd"> <wsp:Policy wsu:Id="policy-c0a22319-6b89-49ff-9b82-bdbac5f04618" xmlns:wsp="http://schemas.xmlsoap.org/ws/2002/12/policy" xmlns:wsa="http://schemas.xmlsoap.org/ws/2004/03/addressing" > <wssp:Integrity wsp:Usage="wsp:Required" xmlns:wssp="http://schemas.xmlsoap.org/ws/2002/12/secext"> <wssp:TokenInfo> <SecurityToken xmlns="http://schemas.xmlsoap.org/ws/2002/12/secext"> <wssp:TokenType> http://schemas.xmlsoap.org/ws/2003/12/kerberos/Kerberosv5ST </wssp:TokenType> <wssp:TokenIssuer>COHOWINERY</wssp:TokenIssuer> <wssp:Claims> <wssp:ServiceName>host/computer1@cohowinery.com</wssp:ServiceName> </wssp:Claims> </SecurityToken> </wssp:TokenInfo> <wssp:MessageParts Dialect="http://schemas.xmlsoap.org/2002/12/wsse#part"> wsp:Body() wsp:Header(wsa:To) wsp:Header(wsa:Action) wsp:Header(wsa:MessageID) wsp:Header(wsa:From)

</wssp:MessageParts> </wssp:Integrity> </policies>

Retrieve certificate from storepublic X509SecurityToken GetSecurityToken() {

X509SecurityToken securityToken = null; X509CertificateStore store = X509CertificateStore.CurrentUserStore( X509CertificateStore.MyStore); bool open = store.OpenRead();

try { byte[] certHash = {0x98, 0xec, 0x08, 0x4b, 0xa5, 0x7a, 0x6c, 0x2f, 0x39, 0x26, 0xb3, 0x0a, 0x58, 0xbf, 0x65, 0x25, 0x61, 0xc5, 0x64, 0x59}; X509CertificateCollection certs = store.FindCertificateByHash(certHash);

Microsoft.Web.Services2.Security.X509.X509Certificate cert = ((Microsoft.Web.Services2.Security.X509.X509Certificate) certs[0]);

if (cert == null) … else if (!cert.SupportsDigitalSignature || (cert.Key == null)) … else { securityToken = new X509SecurityToken(cert); } } finally { if (store != null) store.Close(); } return securityToken;

}

Code for signing SOAP messages Call GetSecurityToken() to retrieve certificate X509SecurityToken signatureToken = GetSecurityToken();

Get the SoapContext method for the SOAP request made to the Web service. Service1 svc = new Service1(); SoapContext requestContext = svc.RequestSoapContext;

Add the client's X.509 certificate to the SOAP header. requestContext.Security.Tokens.Add(signatureToken);

Create a new instance of the MessageSignature class by using the X.509 certificate just added to the SOAP header. MessageSignature sig = new MessageSignature(signatureToken);

Add the digital signature to the SOAP header. RequestContext.Security.Elements.Add(sig);

Specify the TTL for the SOAP message requestContext.Security.Timestamp.TtlInSeconds = 60;

Call the Web service. svc.sayHello();

STEP III

Verify Digital Signatures of SOAP Messages

Signed by an X.509 Certificate

Configure application to validate digital signatures for incoming SOAP messages Export and Import the CA certificate chainAdd a reference to the Microsoft.Web.Services2

assembly When the SOAP message recipient is a Web

service client, this configuration entry is not required. Else configure web.config as below:

<configuration> <system.web> <webServices> <soapExtensionTypes> <add type="Microsoft.Web.Services2.WebServicesExtension, Microsoft.Web.Services2,Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" priority="1" group="0"/> </soapExtensionTypes> </webServices> </system.web></configuration>

Code to verify if SOAP Body is signed

public string CheckSOAPBody() { SoapContext requestContext = RequestSoapContext.Current; // Verify that a SOAP request was received. if (requestContext == null) { throw new ApplicationException("Either a non-SOAP " + "request was received or WSE is not properly " + "installed for the Web application hosting the " + "Web service."); } // Check if the Soap Message is Signed. if (!IsMessageSigned(requestContext)) { throw new ApplicationException("The request is not signed."); } return "sucess";}

Code to verify digital signature of SOAP request

private bool IsMessageSigned(SoapContext context){ foreach (ISecurityElement element in context.Security.Elements) { if (element is MessageSignature) { // The given context contains a Signature element. MessageSignature sig = element as MessageSignature; if ((sig.SignatureOptions & SignatureOptions.IncludeSoapBody) != 0) { // The SOAP Body is signed. return true; } } } return false;}

References

http://www.ietf.org/rfc/rfc2510.txt

http://msdn.microsoft.com/en-us/library/system.security.cryptography.x509certificates.x509certificate(VS.71).aspx

http://msdn.microsoft.com/en-us/library/ms820022.aspx

http://support.microsoft.com/kb/315588

http://msdn.microsoft.com/en-us/library/ms819944.aspx

http://www.codeproject.com/KB/cpp/X509Certificate.aspx

http://www.codeproject.com/KB/WCF/Senthil.aspx