A digital signature is a way to check the authenticity of a digital message or document. A valid digital signature is a proof that a message or document has been created by a well-known author, and that she has reached the recipient in the unmodified form. The text that follows will first be about the digital certificate, then how the user signature is inserted into the Excel, the digital certificate is appended and the digital signature of the document is generated.
How does a digital signature come about? Based on the author and password data, a special algorithm creates a file that keeps the encryption key, which is a digital certificate. This certificate is stored in the file with the PFX extension. Starting the file automatically starts the import process by the operating system and placing it into the digital certificate repository. Digital certificates can be created by the user independently, with the help of programs such as Adobe Acrobat Reader, and can also be obtained from an authorized certification body. This other way is a prerequisite for their business use, since in this way the owner’s identity is guaranteed.
To create a digital signature, we need to open a new file first, enter some data and save it. Then, we can assign a signature to a file. Signature is not a prerequisite for creating a digital signature, but often those who send or receive documents like to see it as evidence of authenticity. We can create it by opening the Signature Line menu on the Insert toolbar, and then selecting the Microsoft Office Signature Line option. A dialog window will open where we can enter the name, function and e-mail address of the signer. Optionally, the instructions to the signatory can also be added. The dialog window offers two more optional fields. First, it allows you to show the date of the signature, and secondly, the signer adds comments to the signature. After confirming the desired options, an image will be generated which we can use as a document signature site.
Right clicking above the signing place opens the context menu in which we can select the Sign option. This option is used to digitally sign the document. Digital signing is a process in which a digital certificate is taken and attached to a document. Thus, the “signed” document can no longer be changed, as this violates the digital signature. In this way, the authenticity of the document is ensured, because if the digital signature is unchanged, it is proof that no document has been changed. After clicking on the Sign dialog box opens in which we first choose whether we will enter the name of the authorized person or we will add the image that represents the facsimile of his signature (in this case we add the picture). Clicking Details opens a dialog window where we can enter some additional information about the signer. By clicking on Change, we can choose which digital signature we will use. In our case, only one digital signature with the name John Doe (the PFX certificate file we imported into the system) is installed. By clicking the Sign button, a digital signing of the document is done. At the same time, Excel marks the document as the final version and recommends that the document is not recommended to be changed. Proof that a document has a digital signature is a modified signature signature site, as well as a special icon that appears in the status line.
In the Excel document it is possible to add a digital signature without adding a signature line. We do this by clicking on the File tab in the Background View, and in the Info group of options, we open the Protect Workbook menu and select the Add Digital Signature option. A dialog box will open, where you will first need to select the Commitment Type in the drop-down list. It can be None (no obligation), Created and approved this document, Approved this document, or Created this document. Then, by clicking Details, we can supplement the signature with additional information about the signer, or by clicking Change, select another digital certificate (if multiple digital certificates are installed). By clicking the Sign button, a digital signing of the document is done, and at the same time Excel denotes the document as the final version.
If we want to change a document with a digital signature, it will cease to be valid. Also, we can manually remove the digital signature from the document. When we finish all the changes and decide to re-add the digital signature, the described procedure for assigning a digital signature should be repeated.