A digital signature is used to validate the authenticity of an electronic message. In order to produce a digital signature, a digital certificate is required.

Mark scheme

Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.

1. [3] Any three from MP1 enquiry made to Certificate Authority (CA) MP2 enquirer's details checked by CA MP3 if enquirer details verified by CA then public key is agreed MP4 CA creates/issues certificate that includes the enquirers public key MP5 encrypting data sent to/by CA with the CA's public/private key
2. [3] MP1 The message is hashed with (the agreed hashing algorithm)... MP2 to produce a message digest MP3 The message digest is then encrypted with the sender's private key to form the digital signature
3. [4] Any four from MP1 The message together with the digital signature is decrypted using the receiver's private key MP2 The digital signature received is decrypted with the sender's public key to recover the message digest sent MP3 The decrypted message received is hashed with the agreed hashing algorithm to reproduce the message digest of the message received MP4 The two message digests are compared MP5 if they are the same the message has not been altered // if they are different the message has been altered