General Cryptographic Schema Flashcards
General model for network security
- A message is to be transferred from one principal (Sender) to another (Recipient) across some sort of Internet service.
- A logical information channel is established by defining a route through Internet from source to destination and by principals’ cooperative use of communication protocols (e.g., TCP/IP).
- All techniques that provide security have two components:
- security-related transformation on info being sent
a. encryption - unreadable by opponent AND/OR
b. addition of a code to verify sender identity of
sender (MAC)
- secret information shared by two principles
a. encryption key to scramble the message - A trusted third party may be needed to achieve secure transmission of secret information
What is encryption?
E(Key1, Plaintext) -> Ciphertext C (transformation or a function E that takes input, key and plaintext to generate a ciphertext C)
What is decryption?
D(Key2, Ciphertext) -> Plaintext P (transformation or a function D that takes input, key and ciphertext to generate a plaintext P)
What is plaintext?
text that can be read and understood by a human
What is ciphertext?
text that is transformed so it needs to be processed to be understood
What is a cipher?
a function that performs encryption and decryption
What is a symmetric algorithm?
Key1 = Key2 (encryption and decryption keys are the same) this means, they can easily be derived from each other
What is asymmetric/ public-key algorithm?
Key1 NOT EQUAL to Key2 (encryption and decryption keys are different) this means, they cannot be derived from each other.
Public key can be published without compromising the private key
What does security depend on?
depends only on the secrecy of the key and not the algorithms
Lecture 2.1 example (slide 12) for 26 alphabets - map each letter to a number (Start at 0)
C = E(K, P) = (P + K) mod 26 P = D(K, C) = (C − K) mod 26
