# Computing - Encryption

> Source: https://ollybritton.com/notes/a-level/computing/topics/encryption/ · Updated: 2020-10-16 · Tags: computing, school, safe-to-post-online

##### What is a summary of encryption??
A way of making sure data cannot be understood if you don't possess the means to decrypt it.

##### What is a Ceasar cipher??
A method of encryption where you shift the letters along by a consistent amount.

##### What is a brute-force attack??
Where you attempt every possible key to decrypt ciphertext until one works.

##### What is another name for a one-time pad??
A Vernam cipher

##### What is another name for a Vernam cipher??
A one-time pad

##### What is a Vernam cipher??
Where a random one-time pad greater or equal in length to the plaintext is exchanged and used to encrypt a message.

##### What is the advantage to a Vernam cipher??
It is completely unbreakable.

##### Why can't you use a one-time pad multiple times??
Because eventually the message will be able to be decrypted with frequency analysis.

##### What's an example decoding scheme for a Vernam cipher??
Do an XOR with all the bits of the message and the key.

### 2022-06-05
##### What is a digital signature??
A method for ensuring the authenticity of an encrypted message.

##### How can messages encrypted with a private key be decrypted??
Using the public key.

##### Why might you want to encrypt something with your private key??
To make a digital signature.

##### What is typically encrypted with a private key when trying to send a digitally signatured message??
A hash of the message's contents.

##### What does a recipient do to check a digital signature accompanying a message??
Hash the message and compare it to the decrypted digital signature using the sender's public key.

---
Olly Britton — https://ollybritton.com. Machine-readable index: https://ollybritton.com/llms.txt