what do you mean by secure digital signature

Dear Dinkar Vidyarthi,

A digital signature (not to be confused with a digital certificate) is an electronic signature that can be used to authenticate the identity of the sender of a message or the signer of a document, and possibly to ensure that the original content of the message or document that has been sent is unchanged. Digital signatures are easily transportable, cannot be imitated by someone else, and can be automatically time-stamped. The ability to ensure that the original signed message arrived means that the sender cannot easily repudiate it later.

A digital signature can be used with any kind of message, whether it is encrypted or not, simply so that the receiver can be sure of the sender's identity and that the message arrived intact. A digital certificate contains the digital signature of the certificate-issuing authority so that anyone can verify that the certificate is real.

According to sec.2(1)(p) of ITAct 2000 means authentication of any electronic record by a subscriber by means of an electronic method in accordance with the provisions of sec.3.It is a valid method of authentication.Varification of the electronic record is done by the use of public key of the subscriber(sec.3(3)).The public Key and private key are unique to the subscriber and constitute a functioning "key pair'".Sec 2(1)(x) defines the term "key pair".

I agree with  both Shree and Shine.

Yes. I too agree

Let me further add that, it 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 ITA 2000. It is a secure,digital code attached to an electronically transmitted message that uniquely identifies and authenticates the sender. These are especially important for electronic commerce and are a key component of many electronic message-authentication schemes.Several States passed Legislation recognising the legality of digital signatures.

A secure digital sgnature is one which adheres to cryptographic standards and one whoch ensures authenticity and non-repudiaiton. Simpley put this means that when one affixes his digital signature he and others should be able to later ascertain that he and he alone has signed using his digital signature. Further when one affixes his digital signature on a document, he should later not be bale to say that he did not sign it.

To achieve all this there are various cryptographic alogrithms used so that hackers are not able to hack a digital signature. Presently in India , I think SHA-256 algorithm is beig used.

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Digital Signature is easy andsecure. Useful links: Digital Signature Application | Digital Signature Certificate Delhi

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A digital signature authenticates the document up to the point of the signing computer, it doesn't authenticate the link between that computer and its user. Related matter has also been discussed in detail this thread https://www.lawyersclubindia.com/forum/digital-contracts-26637.asp

Digital signatures can also be attacked, details are discussed here https://www.unirc.it/firma/en/attack_en.html