Intro to Cryptography Flashcards
state Kerckhoffs’ principle
a cryptosystem should be
secure even if everything about the system, except the key,
is public knowledge.
what are the goals of a cryptosystem
Confidentiality
Authenticity
Integrity
Nonrepudiation
what is the difference between pseudo random numbers and truly random numbers?
The difference between true random number generators (TRNGs) and pseudo-random number generators (PRNGs) is that TRNGs use an unpredictable physical means to generate numbers (like atmospheric noise), and PRNGs use mathematical algorithms (completely computer-generated).
What are the two Encipherment Modes
Stream cipher and block cipher
what are advantages and disadvantages of stream cipher?
Advantage •Speed of transformation •Low error propagation Disadvantage •Low diffusion •Susceptibility to malicious insertion and modifications
what are advantages and disadvantages of block cipher?
Disadvantage •Slowness of encryption •Error propagation Advantage •Diffusion •Immunity to insertion
what are shannon’s characteristics of a good cipher?
•The amount of secrecy needed should determine
the amount of labor appropriate for encryption and decryption
•The set of keys and the encryption algorithm should be free from complexity
•The implementation of the process should be as simple as possible
•Errors in the ciphering should not propagate and cause corruption of
further information in the message
•The size of enciphered text should be no larger than the
text of the original message
what are the reasons for kerchoffs principle
Algorithms are difficult to change
•Cannot design an algorithm for every pair of users
•Expert review
•No security through obscurity!
what is confusion?
The interceptor should not be able to
predict what changing one character in
the plaintext will do to the ciphertext
what is diffusion?
The characteristics of distributing the
information from single plaintext letter
over the entire ciphertext
what are the types of cryptanalytic attacks
Ciphertext only
only knows encryption algorithm and ciphertext, goal is to identify plaintext
Known plaintext
know encryption algorithm and one or more plaintext &
ciphertext pairs formed with the secret key
Chosen plaintext
know encryption algorithm and can select plaintext and obtain ciphertext to attack cipher
Chosen ciphertext
know encryption algorithm and can select ciphertext and obtain plaintext to attack cipher
Chosen text
know encryption algorithm and can select either plaintext or ciphertext to en/decrypt to attack cipher
what is unconditional security
no matter how much computer power is
available, the cipher cannot be broken since the
ciphertext provides insufficient information to
uniquely determine the corresponding plaintext
what is computational security
given limited computing resources (e.g. time
needed for calculations is greater than age of
universe), the cipher cannot be broken
