Digital Signature

Digital signature is one of the most important applications of PKI technologies. In this section we will briefly describe what a digital signature is and how it is produced.

Digital Signature

You may be wondering, what if I use my private key to encrypt a message? Can I decrypt the message with my public key? You are absolutely right. But this process is called signing a message. Just like signing your name on a paper document, you can sign an electronic document, Microsoft Word document for example, with your private key. Remember a document signed with your private key can only be verified with your public key. So any electronically signed documents must be from you and not from anyone else if they can be verified with your public key because only you have your private key - no body else does.

Hash Functions

In real world applications a document or message is not directly signed with your private key for the following reasons.

1. The signed document or message size would double.
2. Signing process would be slow.

Instead a document or message is first digested with a hash algorithm, and then the digest or hash value is encrypted with a signer's private key. When verifying a digital signature the original document or message is digested using the same hash algorithm. The computed hash value is then compared with the hash value decrypted using the signer's public key. If they match then you are sure the document has not been modified after being signed.

Remember that any changes to a document, even a single bit, will result in different hash value or digest. This guarantees that a signed document or message is tamper proof.

Digital Signature: How iSafeguard™ Works

iSafeguard™ works in the same way.

In addition iSafeguard™ support signing and encrypting which ensure privacy, integrity, authenticity and non-repudiation. Here is how it works.

A message is first digitally signed in the way described above and then encrypted in the way described in section Encryption: How Does iSafeguard™ Work?.

Digital Signature Law

The Millennium Digital Commerce Act of 2000 former President Bill Clinton signed makes it legal to utilize digital signature to sign checks, credit and loan applications and many other legally binding documents.

It is not complete to talk about digital signature without mentioning digital certificate which the topic of the next section.