How to Create Digital Signature in PDF and Microsoft Word Files

What is digital signature?

Digital signature plays a crucial role to maintain authenticity, integrity and non-repudiation of data. Once a document is digitally singed then the receiver of that document can be assured to a great extent that the message sent by an authentic user, data is not modified in the way by anyone and no one else except that sender has sent the message.it is almost impossible to fake a digitally signed document, this is way digital signature is so important in electronic commerce industry. Apart from VeriSign, a number of third-party Certificate authorities sell CA (certificate authority); some even distribute free digital certificates. So, the bottom line for digitally sign an electronic document is that: at first you need to have a CA issued by a third-party company trusted by the e-commerce industries, and then sign the document using that CA.

There are many commercial third-party certificate authorities from which you can either purchase a digital certificate or obtain a free digital certificate. Many institutions, governments, and corporations can also issue their own certificates

Digital signature cannot be applied in any electronic documents, unless there is a digital certificate. These digital certificates are issued by third party entities trusted by all. Such type of third party CA issued by VeriSign-the most trusted CA of the world.

How digital signature works?

For digital signature public key algorithm or system is used, where a pair of keys is used for encryption and decryption of data. In this process each user will have a pair of public key and private key-the private key is always kept with the user and the public key shared with everyone who wants to decrypt the message from those specific users only. Normally, the actual message is encrypted with the sender’s private key and the receiver of the message decrypt the message with the sender’s public key, which is publicly available via CA. Usually, RSA algorithm is used in public key system. This process of digital signature is efficient only when the message length is short.

Public key encryption is not an efficient technique for longer message, because it’s a complex process and takes longer time to encrypt and decrypt messages, which proportionately depends on the length of the message. In this case, a slightly different approach is used to make public key encryption an efficient method for digital signature. Instead of sending the entire message encrypted, the user make a specific length of digest of the message and that digest if encrypted with the public key and send to the destination.

The digest of a message (e.g. a word/pdf file) is created by a special function called hash function. The two most commonly used has functions are: MD5 and SHA-1. The digest length of MD5 is only 120 bit and 150 bit for SHA-1. Thus, when this small length of digest is encrypted, it creates much smaller size file, which takes a little time to decrypt.

Note- Digital signature does not provide privacy-it only provides data authentication, integrity and non-repudiation

Why We Use Digital Signature?

They are four crucial aspects of information or data security- privacy, authentication, non-repudiation and integrity. Except data privacy all the other aspects of information security can be covered and ensured with digital signature.

How to Sign Microsoft Word Document with Digital Signature?

1. Open your work file and put the cursor where ever you want to have you signature to appear on the doc.
2. Now, go the Insert tab, in the text group and click the “signature line” and then “Microsoft Office Signature line”.
3. A “Signature Setup’ box will appear, fill it up with the required information (name, title, email) and click OK. (Keep selected “show sign date in signature line” box).
4. Now right click the signature line (with an X mark) and type your name for digital signature. Click ok. Now, our word file is digitally signed to provide date integrity, authentication and non-repudiation. No one can alter the doc, only possible if the digital sign is removed.

How to Remove Digital Signature in Microsoft Word

To remove digital signature from a word file, just right click the signature file in the document, then select the option of “Remove Signature”.

Adding invisible digital signature

• Microsoft word has an option of adding invisible digital signature, to add this feature in your word file, the following steps are necessary:
• From the office buttion click info
• In permission, select protect document
• Select add digital signature and add the required information for the “purpose of signing this document”
• Then click sign-now your file is digitally signed. After signing the document it will be editable, unless you remove the digital sign from your file.