Digital Signatures: signing the hash
What does it mean to sign the hash of a message? Use a diagram to explain how this works, and how the receiver of the message verifies the signature.
With public key cryptography, a message can be encrypted with the sender’s private key.In this case, the entire message serves as a digital signature
Disadvantages
Speed
Storage requirements
Recipient needs to decrypt even if doesn’t want to verify signature
Alternative:Add a small authentication block to the message
e.g. take the hash of the message and encrypt just the hash with the sender’s private key
The result is a much more compact signature
And is just as secure*
*Actually, at time of writing, this is a slightly contentious issue due to emerging hash function weaknesses