Information Technology (Certifying Authorities) Rules, 2000
4. Creation of Digital Signature.-
To sign an electronic record or any other item of information, the signer shall first apply the hash function in the signer’s software; the hash function shall compute a hash result of standard length which is unique (for all practical purposes) to the electronic record; the signer’s software transforming the hash result into a Digital Signature using signer’s private key; the resulting Digital Signature shall be unique to both electronic record and private key used to create it; and the Digital Signature shall be attached to its electronic record and stored or transmitted with its electronic record.