to encrypt the hash. The digital signature is the encrypted hash along with

information such as the hashing algorithm.

An arbitrary input is converted into a fixed-length value, usually much

shorter by a hash function, which is the reason why the hash is encrypted

instead of the entire message or document. A lot of time is saved by

hashing, which is much faster than signing.

The hash value is unique to the hashed data. A change in the data will result

in a different value.

This characteristic allows the integrity of data which is enabled by others to

validate the signer’s public key to decrypt the hash, which proves that the

data has not changed because it was signed if the decrypted hash matches a

second computed hash of the same data. A compromise to its integrity will

happen if the two hashes do not match, meaning that the data in some way

has been tampered. If the signature was created with a private key that does

not correspond to the public key presented by the signer, an issue of

authentication arises.

A digital signature used with any kind of message, whether it is encrypted

or not, makes the receiver sure of the sender’s identity and that the message

arrived intact.

For both the document and the signer, the digital signature is unique and

binds both of them together. The property of non-repudiation makes it

difficult for the signer to not accept that he has signed a message/ document

assuming that his/ her private key has not been compromised.

The digital certificate, an electronic document that contains the digital

signature of the issuing CA and binds it together with an identity and a

public key, verifies that a public key belongs to a particular person or entity.

The digital signatures and digital certificates can be used to make it easy to

sign all outgoing e-mails and validate digitally signed incoming messages.

The communications and transactions conducted over the Internet are

extensively provided by digital signatures in the form of proof of

authenticity, data integrity, and non-repudiation.

Digital signature classes