CS26117 Module 3: Cryptography

What is cryptography?

A method of protecting information using codes and algorithms

What is encryption?

Transforming plaintext into ciphertext

What is plaintext?

Readable data before encryption

What is ciphertext?

Unreadable data produced by encryption

What is decryption?

Recovering plaintext from ciphertext

What is a cryptographic algorithm?

A computational procedure used to encrypt or decrypt data

What type of cipher is the Caesar Cipher?

Substitution cipher

How does the Caesar Cipher work?

It shifts each letter by a fixed number of alphabet positions

Historically, how many positions did the Caesar Cipher shift letters?

3

What is ROT13?

A Caesar cipher that shifts letters 13 positions

What are cryptographic machines?

Mechanical machines used to encrypt information before computers

How many disks does the Jefferson Disk have?

36

What does the Enigma machine use to indicate encrypted characters?

A set of 26 characters that light up

What is a keyword cipher?

A substitution cipher that uses a key

How does a keyword cipher differ from the Caesar Cipher?

It uses a keyword instead of one fixed alphabet shift

What is another name for a one-time pad?

Vernam Cipher

What is used as the key in a one-time pad?

A completely random set of numbers

How does a one-time pad encrypt a message?

It uses random shifts to move each plaintext letter forward

What are the three main types of cryptographic algorithms?

Symmetric, asymmetric, and hash functions

What does symmetric encryption use?

A single key for encryption and decryption

What is key exchange?

Sharing the symmetric key between sender and receiver

Which are the three symmetric encryption algorithms?

DES, 3DES, and AES

What does DES stand for?

Data Encryption Standard

What block size does the DES encrypt

64 bits

What key size does DES use?

56-bit

Is DES considered secure today?

No, it is considered insecure

What does 3DES do?

Applies DES three times

Which statement about 3DES is correct?

It is slow, outdated, and not secure

What does AES stand for?

Advanced Encryption Standard

Which key sizes does AES use?

128, 192, and 256 bits

What block size does AES use?

128 bits

Which is faster?

AES

What does asymmetric encryption use?

Two keys

What are the two keys used in asymmetric encryption?

Public key and private key

Who can access a public key?

Anyone

Who should guard the private key?

The receiver/key owner

Which are asymmetric encryption algorithms?

RSA and ECC

What does RSA stand for?

Rivest-Shamir-Adleman

What does RSA security rely on?

Difficulty of factoring a large product of primes

What does ECC stand for?

Elliptic Curve Cryptography

What mathematical concept does ECC use?

Elliptic curves over finite fields

What is ECDSA used for?

Creating digital signatures

Which key is used to create an ECDSA digital signature?

Private key

What does ECDH allow two parties to do?

Create a shared key without sending the secret key itself

What are hash functions?

Keyless cryptography

What does a hash function produce?

A fixed-length hash value

What is a hash collision?

When two different inputs produce the same hash

Which of the following is a hash algorithm?

SHA-256

What does MD5 produce?

128-bit hash

Is MD5 considered secure today?

No

What does SHA-1 produce?

160-bit output

Why is SHA-1 deprecated?

It is prone to collision attacks

What is SHA-2 designed to improve?

SHA-1's collision resistance

What does SHA-256 produce?

256-bit hash

Where is SHA-256 widely used?

Digital signatures, blockchain, and certificates

What is a digital signature used for?

To prove a message's origin and that it was not tampered with

Alice digitally signs a document and sends it to Bob.

Which key does Alice use to digitally sign?

Alice's private key

Alice digitally signs a document and sends it to Bob.

Which key does Bob use to verify?

Alice's public key

Which three things can a digital signature establish?

Authenticity, integrity, and nonrepudiation

What does authenticity mean?

The message came from the claimed sender

What does integrity mean?

The document was not changed

What does nonrepudiation mean?

The signer cannot easily deny signing it

What is a digital certificate?

A method of linking a public key to its owner

Who issues digital certificates?

A trusted authority

What does a digital certificate primarily prove?

The identity of the key owner

What is the difference between a digital signature and a digital certificate?

Signature proves integrity; certificate proves key-owner identity

Which key is used to encrypt data in asymmetric encryption?

Public key

Which key is used to decrypt the message in asymmetric encryption?

Private key

Which statement correctly compares symmetric and asymmetric encryption?

Symmetric uses one shared key; asymmetric uses public and private keys

Which algorithm is three rounds of DES?

3DES

Which algorithm uses 128-, 192-, and 256-bit keys?

AES

Which algorithm is based on the difficulty of factoring large numbers?

RSA

Which algorithm allows two parties to establish a shared key?

ECDH

Which algorithm is used to digitally sign data with a private key?

ECDSA

Which of the following is NOT one of the three main cryptographic algorithm types?

Mechanical encryption