1. Is an ordinary cryptographic hash reversible encryption?
- Yes
- No
- Only for short input
Check the answer and reasoning
No
A hash is designed as a one-way digest, not a ciphertext with a decryption key.
CS / A2 level
Security, cryptography and ethics
Symmetric encryption uses shared secret keys; asymmetric methods use related public/private keys. Hashes support integrity checks, and digital signatures bind verification to a private signing key.
Learning objectives
- Explain security, cryptography and ethics using a concrete example.
- Apply the worked method and justify each step.
- Recognise the limitation described in the final check.
The big idea
Symmetric encryption uses shared secret keys; asymmetric methods use related public/private keys. Hashes support integrity checks, and digital signatures bind verification to a private signing key.
Secure design also depends on authentication, permissions, key management and human processes. Ethical analysis considers consent, proportionality, bias and impacts; technical legality and ethical justification are different questions.
Worked example
Which key is used to verify a conventional public-key digital signature?
Follow the solution
The private key creates the signature and its corresponding public key verifies it.
Investigate and explain
Predict the worked result before calculating. Change one input, record the new result, and explain which assumptions still hold.
Use the prediction activity below; a local model appears only where it supports this topic.
Check your understanding
2. Which key is used to verify a conventional public-key digital signature?
- Everyone’s password
- The recipient’s secret session key always
- The signer’s public key
Check the answer and reasoning
The signer’s public key
The private key creates the signature and its corresponding public key verifies it.
3. Does encryption alone stop an authorised user misusing data?
- No
- Yes
- Only in cloud storage
Check the answer and reasoning
No
Permissions, oversight and responsible handling remain necessary after legitimate decryption.