Cybersecurity Foundations HSR Vorlesung 1-5 PART 2: https://card2brain.ch/box/20200731_cysec_foundations_teil_2
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What is Scapy
Scapy is a phyton utility to send, sniff, dissect (aufgliedern) and forge (fälschen) ip packets. It’s used to:
Whats the idea of Cypertext
A cryptographic algorithm is used to encrypt a plaintext message
Message, Plaintext --> [Encryption] -- Ciphertext --> [Decryption] --> Message, Plaintext
What is Kerckhoffs's Princple
A cryptographic system must be secure even if everything about the system, except the key, is public knowledge.
What is a SP-Network
Uses repeated substitution (Replacing bytes with others) and permutation (Swapping bytes around) operations. Repeated for multiple rounds.
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.
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.
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
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