CSNT 181 FINAL EXAM 2025/2026 REVISED QUESTIONS
AND QUESTIONS
Cryptography and Encryption - Cryptography is the science of sending messages in secret code.
Encryption is the use of cryptography to protect data confidentiality
encryption algorithm - a set of steps that can convert readable plaintext into unreadable ciphertext
Cipher - a formula that takes unencrypted plaintext and turns it into an unreadable ciphertext
pseudorandom ciphertext - best algorithms make it very difficult to find any patterns unless you have
the key
work factor - Effort/time needed to overcome a protective measure
Substitution Cipher - replaces each character of a message with a different character. One of the
simplest substitution ciphers is called the Caesar cipher - rotates each character through the order of
the alphabet. ROT13 rotates character 13 places
Key progression - one way to strengthen a substitution cipher is by changing the substitution key
over the course of a message (polyalphabetic cipher) an example Vigenère cipher
One-Time Pad - method where the plaintext message is combined, character by character or bit by
bit with a key composed of a string of random numbers or letters.
Transposition cipher - leave the characters of the plaintext intact; they just shuffle them around to
leave the ciphertext unreadable.
Rail Fence Cipher - Ciphers that write message letters out diagonally over a number of rows then
read off cipher row by row.
Steganography - the art and science of hiding information by embedding messages within other,
seemingly harmless messages
, Digital cryptography - Transport encryption - protects data in transit, such as data being sent over the
network
Storage encryption- protect data at rest, which is on some sort of persistent storage medium
Memory encryption - protects data in use, such as that in system RAM or even that being currently
processed
Digital cryptography (2) - Cryptographic obfuscation - protects the code of a program itself from
those who would try to reverse engineer it, without changing its function. Sometimes used by
malware to hide from scanners
Symmetric encryption - uses a single key to encrypt and decrypt data aka secret or private key
Digital cryptography (3) - Asymmetric encryption - uses two mathematically-related keys: data
encrypted with one can only be decrypted with the other. Also known as public-key cryptography
Cryptographic hashing - converts data into a hash or unique signature. The has can't be turned back
into the original data but can be compared to the data to verify its integrity.
Modern cryptosystems - combine multiple methods, protocol, and algorithms to achieve a set of
security goals. Ex. SSL/TLS connection for secure web sessions use cipher suite including all 3 types of
algorithms as well as a pseudorandom number generator
Communication Theory of Secrecy Systems - 1949 paper considered one of the foundational
documents of modern cryptography
Confusion - making the mathematical relationship between the plaintext and the key as complex as
possible so that a partially correct key is useless to an attacker
Diffusion - breaking up patterns in the plaintext so they won't be at all apparent in the ciphertext so
that known-plaintext contents won't be useful in decoding the ciphertext
ideal cipher - designed to be vulnerable only to brute force attacks that try every possible key in
sequence
AND QUESTIONS
Cryptography and Encryption - Cryptography is the science of sending messages in secret code.
Encryption is the use of cryptography to protect data confidentiality
encryption algorithm - a set of steps that can convert readable plaintext into unreadable ciphertext
Cipher - a formula that takes unencrypted plaintext and turns it into an unreadable ciphertext
pseudorandom ciphertext - best algorithms make it very difficult to find any patterns unless you have
the key
work factor - Effort/time needed to overcome a protective measure
Substitution Cipher - replaces each character of a message with a different character. One of the
simplest substitution ciphers is called the Caesar cipher - rotates each character through the order of
the alphabet. ROT13 rotates character 13 places
Key progression - one way to strengthen a substitution cipher is by changing the substitution key
over the course of a message (polyalphabetic cipher) an example Vigenère cipher
One-Time Pad - method where the plaintext message is combined, character by character or bit by
bit with a key composed of a string of random numbers or letters.
Transposition cipher - leave the characters of the plaintext intact; they just shuffle them around to
leave the ciphertext unreadable.
Rail Fence Cipher - Ciphers that write message letters out diagonally over a number of rows then
read off cipher row by row.
Steganography - the art and science of hiding information by embedding messages within other,
seemingly harmless messages
, Digital cryptography - Transport encryption - protects data in transit, such as data being sent over the
network
Storage encryption- protect data at rest, which is on some sort of persistent storage medium
Memory encryption - protects data in use, such as that in system RAM or even that being currently
processed
Digital cryptography (2) - Cryptographic obfuscation - protects the code of a program itself from
those who would try to reverse engineer it, without changing its function. Sometimes used by
malware to hide from scanners
Symmetric encryption - uses a single key to encrypt and decrypt data aka secret or private key
Digital cryptography (3) - Asymmetric encryption - uses two mathematically-related keys: data
encrypted with one can only be decrypted with the other. Also known as public-key cryptography
Cryptographic hashing - converts data into a hash or unique signature. The has can't be turned back
into the original data but can be compared to the data to verify its integrity.
Modern cryptosystems - combine multiple methods, protocol, and algorithms to achieve a set of
security goals. Ex. SSL/TLS connection for secure web sessions use cipher suite including all 3 types of
algorithms as well as a pseudorandom number generator
Communication Theory of Secrecy Systems - 1949 paper considered one of the foundational
documents of modern cryptography
Confusion - making the mathematical relationship between the plaintext and the key as complex as
possible so that a partially correct key is useless to an attacker
Diffusion - breaking up patterns in the plaintext so they won't be at all apparent in the ciphertext so
that known-plaintext contents won't be useful in decoding the ciphertext
ideal cipher - designed to be vulnerable only to brute force attacks that try every possible key in
sequence
