1.4. Digital Signing of Data

The goal of cryptography is three-fold: keep data secret, identify if data has been modified, and prove the source of the data. Although encryption can keep data secret and protect data against modification, only digital signing proves the source of the data in addition to protecting the data from modification. Digital signing protects data in the following ways:

• The digital signing process uses a hash algorithm to determine whether the original data has been modified in any way.

• A digital signature applied to the resulting message digest identifies who signed the message digest. This signing prevents users from denying they signed the message digest, as only they have access to the private key used to sign the message digest. The inability for signers to deny that a signature is theirs is known as non-repudiation.