CertiGuide to Security+  9  Chapter 4:  Basics of Cryptography (Domain 4.0; 15%)       9  4.2  Concepts in Using Cryptography            9  4.2.2  Integrity

4.2.2  Integrity 1 2 3 4.2.3  Authentication

A Digital Signature is an electronic signature of a document, created by using asymmetric encryption. A digital signature is different from a handwritten signature, because a handwritten signature tends to be the same over time, but a digital signature differs depending on the data being signed. A digital signature is used by a document’s receiver to verify that:

the message has not been tampered with since it was signed (data integrity)

the person who supposedly sent the message really is who they say they are

Typically this is accomplished via encryption with a private key known only by the message sender, and decryption with the public key.

Keep in mind that it is computationally more expensive to encrypt a message than to apply a hashing algorithm to it, that messages sent between parties can be very large (such as file transfers), and the time taken to encrypt data increases the larger the amount of data is. This led researchers to combine the ideas of hashing (with an algorithm like MD5) and encryption, to create a digital signature by encrypting only the document’s message digest hash value, rather than the entire contents of the message.

4.2.2  Integrity 1 2 3 4.2.3  Authentication