A digital signature is a way to ensure the integrity and origin of data.
A digital signature provides strong evidence that the data has not been altered since it was signed and it confirms the identity of the person or entity who signed the data.
A digital signature enables the important security features of integrity and nonrepudiation, which are essential for secure electronic commerce transactions.
Digital signatures are typically used when data is distributed in plaintext, or unencrypted form. In these cases, while the sensitivity of the message itself might not warrant encryption, there could be a compelling reason to ensure that the data is in its original form and has not been sent by an impostor because, in a distributed computing environment, plaintext can conceivably be read or altered by anyone on the network with the proper access, whether authorized or not.
Information Technology Act 2000
2(p) “digital signature” means authentication of any electronic record by a subscriber by means of an electronic method or procedure in accordance with the provisions of section 3;
2(q) “Digital Signature Certificate” means a Digital Signature Certificate issued under sub-section (4) of section 35;
