Is this really from the bank?
You get a message that says "pay Sam 10 pounds". On the way, somebody could change 10 to 90. Somebody could also pretend to be your bank.
Cryptography answers three questions. Can anyone else read it? Was it changed? Who really sent it?
Key words
| Word | What it means |
|---|---|
| Cryptography | Using encryption or hashing so data is sent securely and its sender can be checked. |
| Encryption | Scrambling data so only someone with the right key can read it. It can be reversed. |
| Symmetric encryption | Encryption where one shared key locks and unlocks. |
| Asymmetric encryption | Encryption with a public key and a private key. |
| Digital signature | A mark made with a private key that proves who sent data. |
| Hashing | Turning data into a fixed-length fingerprint. It cannot be reversed. |
| HMAC | A hash made with a secret key, to show data was not changed and who made it. |
| Authentication | Proving that you or your data are who or what you say. |
| MAC | Message authentication code: a short code that goes with a message. |
| Authenticity | Proof that data really came from who it says. |
| Non-repudiation | The sender cannot later deny they sent it. |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can explain the purpose of cryptography and the characteristics of encryption, hashing, digital signatures, HMAC and MAC.
Starter: what you already know
Have a go
Starter: what you already know
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
The purpose of cryptography
Cryptography uses encryption or hashing so data can be sent in a secure way, and its sender can be checked.
Two kinds exist. Encryption can be reversed with a key. Hashing cannot be reversed at all.
Encryption and confidentiality
Encryption gives confidentiality. Only the planned readers can open the data.
Symmetric encryption uses one shared key. It is fast. Asymmetric encryption uses a public key to lock and a private key to unlock. No secret has to be sent first.
Asymmetric keys also make digital signatures. Sign with your private key. Anyone can check with your public key. That gives authenticity.
Check: encryption
Have a go
Check: encryption
4 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.