Q. Consider the following statements with reference to digital signatures in internet communication:

1. By using digital signature, a sender cannot deny a message which he or she has sent to a receiver.
2. Digital signature can be used as legal proof to ensure that the message was sent by a certain sender.
3. Digital signature is used for safe communication between two computers of a closed network.
4. Digital signatures are required to send all email messages.

Which of the above statements is / are correct?
Answer: Only 1 and 2
Notes: Digital signatures provide non-repudiation and authenticate the sender's identity, offering legal proof (statements 1 and 2). However, they are not required for all communications in a closed network, nor for sending all emails. Thus, only statements 1 and 2 are correct, while statements 3 and 4 are incorrect.