A digital signature is a mathematical method or technique used to verify the integrity and authenticity of software, digital document message or e-mail.

The digital equivalent of stamped seal or handwriting signature but providing far better security to solve the problem of impersonation and tempering in communication. A digital signature can provide added assurance of events to the origin, the status of an electronic document, identity, message or transaction as well as notice consent by the signer.

In many countries including the UK, USA digital signature has the same legal verification as the traditional paper-based signed document. In that country, they issue electronic version of public-private law budget with a numeric name

A digital signature is based on some cryptography system like a private key or public key cryptography. A mostly digital signature is based on private key also known as asymmetric cryptography. Using algorithms such as RSA which generate two keys that are mathematical bounded one as private for encryption and another as public for decryption.

To create a digital signature, the assigned software like e-mail system hash function generates a one way hash of the data to be signed. The private key is used to encrypt hash along required other information such as the hashing algorithm. The advantage of encrypting with hash is that is can convert any length of data in a fixed-length format, so it saves the memory space and faster from executing the signing process

The value of the hash is always unique the every hashed date. The hash value of the same data may be posses different hash value, so it is more secure to implement. Any modification in data even deleting or changing a single character results in differences in hash value.

This attribute helps to validate the integrity of the data by using the public key to decrypt the hash. If the decoded value is matched with the hash value of received data, then the message is genuine; otherwise, the data has been tempered or changed on the way. Or the signature was assigned with the private key does not correspond to public key provided by the signer.

Whether the message is encrypted or not a digital signature can be used with any kind. Naturally, the letter arrived at correct form and receiver can be sure about the sender identity. The numeric name is unique so no one can deny that the signed document is not authenticated. The digital certificate with the digital signature is bind with a public key so it can use for the verification of particular parties or persons.

A digital signature is supported by most of the modern email programs, and digital certificate makes it easy to sign any outgoing email, and incoming messages are validated digitally. Data integrity authenticity and non-repudiation of communication transaction are also maintained by digital signature over the internet.