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