VerifySignature Method

Verifies the signature of the current message.

procedure VerifySignature();

Remarks

VerifySignature verifies the signature of the input message.

In order to perform signature verification the public signer's certificate must be present or explicitly specified. In many cases the certificate itself is included in the input message and a certificate does not need to explicitly be set. If a certificate does need to be set for signature verification the certificate may be specified by calling AddRecipientCert or setting RecipientCerts.

When this method is called the SignerCertInfo event fires once for each signature on the message. This event provides details about the signer certificate, as well as the signer certificate itself (if present). The information provided via SignerCertInfo may be used to load an appropriate certificate for verification from within the event. If the CertEncoded parameter of SignerCertInfo is populated the certificate required for verification is already present in the message.

The following property are applicable when calling this method:

• DetachedSignature
• DetachedSignatureData
• EnableCompression
• SignerCerts

If the input message is a detached signature, the original data that was signed must be specified in DetachedSignatureData. In addition the DetachedSignature property must be set to True to instruct the component to treat the input message as a detached signature.

If the input message is compressed EnableCompression must be set to True before calling this method.

Input and Output Properties

The component will determine the source and destination of the input and output based on which properties are set.

The order in which the input properties are checked is as follows:

• SetInputStream
• InputFile
• InputMessage

When a valid source is found the search stops. The order in which the output properties are checked is as follows:

• SetOutputStream
• OutputFile
• OutputMessage: The output data is written to this property if no other destination is specified.

When using streams you may need to additionally set CloseInputStreamAfterProcessing or CloseOutputStreamAfterProcessing.

Sign and Verify a message

Cms cms = new Cms();
cms.Certificates.Add(new Certificate(CertStoreTypes.cstPFXFile, @"C:\temp\test.pfx", "password", "*"));
cms.InputMessage = "My Data";
cms.Sign();

string signedMessage = cms.OutputMessage;

cms = new Cms();
cms.InputMessage = signedMessage;
cms.VerifySignature();

string plaintextMessage = cms.OutputMessage;

Cms cms = new Cms();
cms.Certificates.Add(new Certificate(CertStoreTypes.cstPFXFile, @"C:\temp\test.pfx", "password", "*"));
cms.InputMessage = "My Data";
cms.OutputFormat = "DER";
cms.Sign();

byte[] signedMessage = cms.OutputMessageB; //Binary output

cms = new Cms();
cms.InputMessageB = signedMessage;
cms.VerifySignature();

string plaintextMessage = cms.OutputMessage;

Cms cms = new Cms();
cms.Certificates.Add(new Certificate(CertStoreTypes.cstPFXFile, @"C:\temp\test.pfx", "password", "*"));
cms.InputMessage = "My Data";
cms.DetachedSignature = true;
cms.Sign();

string signature = cms.OutputMessage;

cms = new Cms();
cms.InputMessage = "My Data";
cms.DetachedSignatureData = signature;
cms.DetachedSignature = true;
cms.VerifySignature();

Cms cms = new Cms();
cms.InputMessage = "My Data";
cms.Certificates.Add(new Certificate(CertStoreTypes.cstPFXFile, @"C:\temp\test.pfx", "password", "*"));
cms.Certificates.Add(new Certificate(CertStoreTypes.cstPFXFile, @"C:\temp\test2.pfx", "password2", "*"));
cms.Sign();

string signedMessage = cms.OutputMessage;

cms = new Cms();
cms.InputMessage = signedMessage;
cms.VerifySignature();

string plaintextMessage = cms.OutputMessage;

Cms cms = new Cms();
cms.InputMessage = "My Data";
cms.Certificates.Add(new Certificate(CertStoreTypes.cstPFXFile, @"C:\temp\test.pfx", "password", "*"));
cms.IncludeCertificates = CmsIncludeCertificates.icsNone;
cms.Sign();

string signedMessage = cms.OutputMessage;

cms = new Cms();
cms.OnSignerCertInfo += (s, e) => {
  Console.WriteLine(e.Issuer);
  Console.WriteLine(e.SerialNumber);
  if (e.Issuer == "CN=100") //Identify the certificate to load based on event params
  {
    //Load the correct signer certificate.
    cms.SignerCerts.Add(new Certificate(CertStoreTypes.cstPublicKeyFile, @"C:\temp\test.cer", "", "*"));
  }
};
cms.InputMessage = signedMessage;
cms.VerifySignature();

string plaintextMessage = cms.OutputMessage;