Lernkarten
What is Scapy
Scapy is a phyton utility to send, sniff, dissect (aufgliedern) and forge (fälschen) ip packets. It’s used to:
- to create tools that can probe, scan or attack networks
- ist very powerfool for interactive packet manipulation
- used to create attack signatures for IDS/IPS systems
Whats the idea of Cypertext
A cryptographic algorithm is used to encrypt a plaintext message
Message, Plaintext --> [Encryption] -- Ciphertext --> [Decryption] --> Message, Plaintext
^----------------key-------------------^
What is Kerckhoffs's Princple
A cryptographic system must be secure even if everything about the system, except the key, is public knowledge.
- Algorithms are known public, anyone can text them
- «The enemy knows the system»
- Public exposure may help to find weaknesses more quickly
- Most believe in this principle, but some also think it’s saver to keep the key and the algorithm secret
What is a SP-Network
Uses repeated substitution (Replacing bytes with others) and permutation (Swapping bytes around) operations. Repeated for multiple rounds.
wikipedia: https://en.wikipedia.org/wiki/Substitution%E2%80%93permutation_network
How does the Caesar cipher work
To encrypt a message each letter of the alphabet is shift three letters to the right. It is a substitution cipher that is mono-alphabetic.
Example
Here’s an example of the Caesar cipher in action.
Khuh’v dq hadpsoh ri wkh Fdhvdu flskhu lq dfwlrq.
How does XOR work and why is it interessting for cryptographics
A function which takes 2 inputs returns true if one of the inputs is true and the other is false.
e.g.:
A B O
0 0 0
0 1 1
1 0 1
1 1 0
doing the process again with A and O gives back B again. This is very usefull, because this process can be thought of as A encrypting and decrypting B.
What is the one time pad
The one time pad uses XOR to encrypt and decrypt a message.
+ once the key is gone there is no way using statistics to retreive the original message
- the size of the key is the same as the file e.g. 1 GB file = 1GB key
- if a key is used more than once, the cipher is broken, because it can be reversed then
What is a stream cipher and which advanteages and disadvantages does it have
The idea is to create a one time pad by generating an infinite pseudo random-keystream
- Encryption of long continuous streams possible
- Extremely fast with low memory footprint à ideal for low-power devices
- If designed well it can seek (suchen, ermitteln) to any location in the stream
- The keystream must appear statistically random
- A key + nonce must never be reused
- Stream ciphers do not protect the ciphertext (no guaranteed integrity)
