Digital signatures provide authenticity, integrity, and non-repudiation for electronic documents. They use asymmetric cryptography with a private key for signing and public key for verification. The signer uses their private key to encrypt a hash of the message, creating a digital signature. The recipient can then decrypt the signature with the signer's public key to verify the message has not been altered. Hardware tokens like smart cards and USB tokens store private keys securely. The Controller of Certifying Authorities licenses and monitors Certifying Authorities in India that issue digital signature certificates.