Briefly about digital signatures
You can enabledigital signatures when designing a form so that users can adddigital signaturewhen filling it out. Thisdigital signatureproves that the form originated from the signer and has not been changed. Also thesignaturecan include some comments from the author. After signing, the data in the form cannot be changed without cancellationdigitalsignature.
When adding adigital signature, the user must use adigitalcertificate.Digitalcertificate is an attachment for a file, macro project, or e-mail message that assures authenticity, provides secure encryption, or supplies a verifiablesignature. Digitalcertificates, which you can get through commercial certification authorities or from your internalsecurityadministrator, establish the authenticity of thesignature.
About InfoPath digital signatures
In addition to enablingdigital signatures so that users can sign your form, you can add adigital signature to your form template which authenticates you as the author of the form template in the same way that adigital signature on a form authenticates the user who filled out the form. Form template inInfoPath is a file or set of files that defines the data structure, appearance, and behavior of a form. For example, form templates that have been distributed to users in an e-mail message can be updated more effectively if they have been supplied with adigital signature.
When you put adigital signature ina form,InfoPathuses only those certificates that have a private key and aDigital Signatureor Both value for the Key Usage attribute. Also the purpose of the certificate must be set as Client Authentication or Code Signing. If you are using a certificate to adddigital signatureto a form template, the certificate must be set as Code Signing. These limitations are applied becauseInfoPathuses XMLSignaturesto digitally sign forms.
Because adigitalcertificate you create is not issued by a formal certification authority, forms signed using a certificate you created are referred to as self-signed forms. These certificates are considered unauthenticated and will generate asecuritywarning if the form’ssecuritylevel is set to Domain.InfoPathtrusts self-signed certificates only on computers that have access to the private key for that certificate. In most cases, this means thatInfoPathtrusts self-signed certificates only on the computer that created the certificate, unless the private key is shared with other computers.
Signatures can be added to forms by going into Tools > Form Options > Security and Trust (Visual Studio 2005). Each self-signed digital signature has an expiry date and would need to be re-generated after that date.