You can protect the integrity of forms by allowing people to use certificates to digitally sign forms. After the form is signed, the signed portion cannot be altered without invalidating the signature. The digital signature invokes a third-party signature handler that provides the required digital signature functionality.Verifying the signature guarantees that no one tampered with the data after it was submitted. When someone signs a form, a message digest of the data to be signed is created, and a mathematical computation combines the person’s private key with the specified form data and encrypts them together. The output is a digital signature. This digital signature contains the signed data and the certificate information associated with the person who signed the form.When the signature is verified, the individual’s public key is used to decrypt the signed data and to obtain the digest value. The new digest value is calculated against the received document by using the same algorithm of the signing process. If the two digest values do not match, this means that the data has been tampered with since the form was signed, and the verification fails.Digital signatures also bind certificates to the signed data. The certificate included in the signature can be authenticated to validate the identity of the person who signed the data.The individual must have a digital certificate from an appropriate certificate issuer to sign the form. Adobe signatures support the Public Key Cryptography Standard (PKCS) #7, using the RSA MD5, RSA SHA-1 or DSA SHA-1 hash algorithm.LiveCycle Designer ES contains the following two types of digital signatures.Document signatures protect the appearance of form objects and the values they hold. To create a document signature, add a signature field to the form design. You can specify whether a document signature applies to an entire form or to a collection of objects on a form. By default, it applies to the entire form. If you want the document signature to apply to a collection of form objects, the signing party must use Acrobat or Adobe Reader 8.0 or later.If the document signature applies to a collection of objects, it ignores static objects, such as circles and rectangles. It applies only to buttons, check boxes, date/time fields, decimal fields, drop-down lists, image fields, list boxes, numeric fields, paper forms barcodes, password fields, radio buttons, other signature fields, and text fields.To sign the form, the user clicks the signature field. If the document signature applies to a collection of form objects, the objects specified in the signature are locked and set to read-only. Locking the objects prevents form recipients from changing the object values after the document is signed.Data signatures secure the form data and guarantee the data integrity during transmission. To create a data signature, add a submit button, email submit button, or HTTP submit button, and select the Sign Submission option in the Object palette. To sign the data, the signing party must use Acrobat or Adobe Reader 8.0 or later.Data signatures can apply to the form data only or to the entire submission, including any attachments such as annotations, document signatures, or PDF documents.To sign the form data, the user clicks the submit button. When a user clicks the button, they must provide their signing certificate so that their digital signature is applied to the form data before it is submitted.