CSE 3400 - Introduction to Cryptography and Cybersecurity

class notes

Cryptography is the study of secure _____ in the presence of an __________.

communication, adversary

An adversary is an ______

attacker

Modern cryptography is treated as a ____ ____ rather than art

mathematical science

Modern cryptography focuses on __________ security rather than secrecy of the _____.

provable, algorithm

In modern cryptography, the ultimate goal is to produce a ______ _______ _______

proof of security

Because not everything can be proven secure, modern cryptography relies on __________

assumptions

Historical cryptography often relied on security through __________.

obscurity

security through obscurity means the ____ itself is kept secret

algorithm

If a historically secret algorithm is leaked, the entire system must be __________.

redesigned

Kerckhoffs’s Principle states that a cryptographic system should remain secure even if the attacker knows the entire __________.

algorithm

According to Kerckhoffs’s Principle, security should depend ONLY on the secrecy of the __________.

key

A cryptographic assumption is a problem believed to be ____ ____ to solve efficiently.

computationally hard

In the eavesdropper model, the adversary can __________ to the communication but cannot ____ it.

listen, modify

A symmetric encryption scheme consists of __________ algorithms.

3

The algorithms in a symmetric encryption scheme are ___ ___, ___, and ___

key generation, encryption, decryption

Symmetric Encryption Scheme:

The encryption algorithm takes a ___ ___ “k” and a ____ “m” and outputs a ___

The decryption algorithm takes a ___ ___ “k” and a ____ “c” and outputs the original ___

The only piece of information unknown to the adversary is the ___ ___

secret key, message, ciphertext, secret key, ciphertext, message, secret key

Correctness requires that decrypting an encrypted message returns the ___ message

original

The shift cipher is an example of __________ encryption.

The key space of the shift cipher consists of the numbers ___ ___ ___

The shift cipher is insecure because its___ ___ is too __

symmetric, 0 through 25, key space, small

The sufficient key space principle states that the key space must be large enough to prevent __________ attacks.

brute force

The security parameter measures how __________ a system is to break.

hard

Increasing the security parameter usually increases both ___ and ___ ___

security, computational cost

A substitution cipher replaces each letter with a unique ___

The key space contains __ possible keys

It’s still insecure due to __ in the language

letter, 26!, patterns

In symmetric encryption, Alice and Bob share the same ___ ___

secret key

In symmetric encryption the SAME key is used for ____ and _____

encryption, decryption

The Vingenere cipher is a type of ____ cipher

polysubstitution

A polysubstitution cipher replaces ___ ____ ____ instead of individual letters

blocks of letters

In a block cipher, the key defines a ___ of blocks

permutation

Vingenere Cipher: the advesary knows the ___ ___ but not the actual ___

block size, permutation

Vingenere Cipher: increasing the block size helps ____ ____ in the plaintext

break patterns

Vingenere Cipher: the LARGER the block size, the ___ the key must be

larger

Vingenere Cipher: a major drawback of LARGE BLOCK SIZES is increased ____ ____ and ___ cost

key size, decryption

In general, the larger the key, the more ___ the ___

secure, encryption

classical ciphers are completely ____ by modern standards except when the key is as ___ as the message

insecure, long

The One-Time Pad is a historical cipher that is ____ ____ by modern definitions

perfectly secure

In one-time pad (otp):

the message is an ___ bit string

the KEY must be the ___ length as the message

decryption is performed using the same ____ operation as encryption

n, same, XOR

The XOR of a bit with 0 always equals the ____ _____.

original bit

The XOR of a bit with itself always equals _____.

0

Correctness means that
Dec(K, Enc(K, m)) = _____.

m

A One-Time Pad preserves _____ structure in the ciphertext.

no

Given a ciphertext, every possible plaintext is _____ likely under OTP.

equally

OTP cannot be broken by _____ ___ search.

brute force

OTP is impractical because it requires a _____ key for every message.

unique

Security means the adversary learns no ___ ___ from the ___

new information, ciphertext

In the privacy experiment, the oracle first generates a ___ ___

The ____ chooses two messages of _____ length.

The oracle picks a random bit from the set _____.

The adversary wins if it correctly guesses which _____ was encrypted.

An encryption scheme is secure if the adversary’s probability of winning is at most _____.

A probability higher than 50% means the scheme _____ information.

secret key, adversary, equal, {0,1}, message, 50%, leaks

message length cannot be hidden in the ___ model

eavesdropping