Higher Computing Science
Digital signatures and digital certificates
Higher Computing Science: Computer systems
Digital signatures and digital certificates sound alike, and the 2025 examiners' report noted that candidates mix them up. They answer two different questions.
Two different questions
| Digital signature | Digital certificate | |
|---|---|---|
| Answers the question | Who sent this, and has it been changed? | Does this public key really belong to who it says? |
| Shows | The message came from the sender and has not been altered on the way | A trusted certificate authority has checked that the key belongs to the organisation |
| Example | A garage's invoice email, signed so the customer knows it is genuine and unchanged | The padlock on a shop's website: its key has been confirmed by an authority |
Where the keys come in
- With public key encryption, data is encrypted with the receiver's public key, which anyone may have, and can only be decrypted with the receiver's private key, which only they hold.
- A digital signature is made with the sender's private key, and anyone can check it with the sender's public key. If the message is changed, the check fails.
- A digital certificate holds an organisation's public key and confirms it is theirs, so you know you are using the right public key.
- "A digital signature shows the email came from the garage and has not been changed."
- "A digital certificate confirms the shop's public key belongs to the shop."
- "It makes it secure." Too vague: say what it shows.
- "A signature encrypts the email so no one else can read it." That is what encryption does.
When a question asks why an organisation would use both, give one point for each: the certificate confirms its public key, and the signature proves each message is genuine and unchanged.
Try two exam-style questions
Choose an answer, say how sure you are, then press Check. Every wrong answer tells you why it is wrong.
The full course covers every topic like this. Every topic in Higher Computing Science has a short note, and a practice quiz with feedback on every answer, plus coding lessons in Python, SQL and HTML, a full mock exam and a progress report for parents.
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This site is independent: it is not connected to the SQA or Qualifications Scotland. Points from the examiners' course reports are given in our own words.