What do you mean by digital signature and electronic signature under The Information Technology Act, 2000 ?

"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 of the Information Technology Act 2000 (Act). [Section 2(1) (p)] "Electronic signature" means authentication of any electronic record by a subscriber by means of the electronic technique specified in the Second Schedule and includes digital signature. [Section 2(1) (ta)] According to section 3 of Information Technology Act, 2000, Digital signature (i.e. authentication of an electronic record by a subscriber, by electronic means) is recognised as a valid method of authentication. The authentication is to be effected by the use of"asymmetric crypto system and hash function", which envelop and transform electronic record into another electronic record. Verification of the electronic record is done by the use of a public key of the subscriber. The private key and the public key are unique to the subscriber and constitute a functioning "key pair". Section 3A of the Act deals with electronic signature. Section 3A(1) provides that notwithstanding anything contained in section 3, but subject to the provisions of section 3A(2), a subscriber may authenticate any electronic record by such electronic signature or electronic authentication technique which- is considered reliable; and may be specified in the Second Schedule. For the purposes of above any electronic signature or electronic authentication technique shall be considered reliable if - the signature creation data or the authentication data are, within the context in which they are used, linked to the signatory or, as the case may be, the authenticator and to no other person; the signature creation data or the authentication data were, at the time of signing, under the control of the signatory or, as the case may be, the authenticator and of no other person; any alteration to the electronic signature made after affixing such signature is detectable; any alteration to the information made after its authentication by electronic signature is detectable; and it fulfils such other conditions which may be prescribed. Central Government may prescribe the procedure for the purpose of ascertaining whether electronic signature is that of the person by whom it is purported to have been affixed or authenticated.