D830 - Introduction to Cryptography

Ceasar Cipher

Encryption technique that shifts the alphabet by a certain number of characters

Block Cipher

Breaks data into chunks and encrypts each chunk using a key.

Stream Cipher

Algorithm that takes one character and replaces it with one character.

Transposition Cipher

Encryption technique that only rearranges the characters themselves. Does not change them

One time pad

A type of Vernam Cipher that encrypts plaintext using XOR with a truly random key that is the same length as the plaintext. Used only once.

Vernam Cipher

Symmetric Encryption method that uses XOR with plaintext and a key. No restrictions

Quantum Computing

Perform complex, fast computations using Qubits. It threatens current encryption by rapidly solving mathematical factorization (RSA).

Quantum Cryptography

Method of secure communication that uses the laws of physics to detect eavesdropping and securely exchange keys.

Shannon's Principle

Always assume your adversary has a copy of your cipher text/algorithm, therefore key secrecy is the only thing that matters. Modern version

Cryptanalysis

Science of breaking cryptography, created by William Friedman

Alan Turning

introduced the concept that machines could perform mathematical computations. He broke the German Enigma code.

Kerckhoff's Principle

The strength of a cryptosystem depends on the secrecy of the key, not the algorithm itself.

Moore's Law

The number of transistors on a chip doubles every 18 months while prices half.

Shannon's confusion?

Hiding the relationship between the key and the ciphertext.

Shannon's diffusion

Spreading one plaintext across many ciphertext bits to hide patterns.

Diffie-Hellman revolution

Method that allows two parties to securely create a shared secret over a public channel.

Phil Zimmerman and PGP

Pretty Good Privacy encryption program created to secure messages, mainly email , using both symmetric and asymmetric encryption.

RSA Algorithm

Asymmetric encryption algorithm that uses a public key for encryption and private key for decryption.

Message (m)

Cleartext or Plaintext

Key Space

All possible keys that can be used with an algorithm.

Algorithm

Method used to encrypt and decrypt data.

Key

Secret value used by an algorithm to produce a unique encrypted result.

Initialization Vectors (iv)

A random starting value used in the first block of encryption to ensure identical plaintext produces different ciphertext.

Work Factor

Time and resources required to break cryptographic protection through unauthorized means.

Higher work factor means

More secure

Known Plaintext Attack (kpa)

When an attacker has both the plaintext and its corresponding ciphertext to discover a key.

IV attack

Attack that targets weak or reused initialization vectors to break encryption. Think of WEP

Timing attack

Attack that measures the time it takes to perform a cryptographic operation to gain info about a key.

Frequency Analysis

Attack that studies how often letters or patterns appear in ciphertext to guess plaintext.

Ciphertext-only attack

The attacker only has access to ciphertext and tries to recover the plaintext of a key.

Chosen Attack

Attack where the attacker chooses specific inputs to be encrypted or decrypted and see's how it behaves.

Chosen plaintext Attack (CPA)

Attacker chooses plaintext and sees how it encrypts

Chosen Ciphertext Attack (CCA)

Attacker chooses ciphertext and sees how it decrypts.

Mathematical analysis

Attack that uses math techniques to break an encryption algorithm or recover the key.

Linear Analysis / Cryptanalysis

Attack that uses linear approximations, aka pattern recognition thats almost true all the time, to describe patterns and relationships.

Differential Analysis / Cryptanalysis

Attack that studies how differences in plaintext affect differences in ciphertext to recover a key. Looks at how changes affect output.

Out-of-band key exchange

Method of sharing a key using a separate and secure communication channel outside the main network. Mostly for symmetric keys.

Symmetric Key advantages

Faster, encrypts larger bulks of data better, streaming media, and free algorithms like AES

RC4

Stream Cipher - encrypts data one bit at a time using a keystream. Fast but insecure. Used in WEP

RC6

Block Cipher - encrypts fixed-size blocks of data (128 bits) at a time. More complex and secure

DES

Outdated and weak block cipher, only 56 bits and can be easily brute forced.

AES

Secure and widely known block cipher considered strong and resistant to known practical attacks. Strong only if implemented correctly.

AES bit sizes

128/192/256 bits

Confusion vs Diffusion

Hides the relationship between the key and ciphertext vs Spreads the influence of one plaintext bit across many ciphertext bits.

ECB (Electronic Codebook)

Does not use an IV, which results in an identical plaintext being encrypted into identical ciphertext. BAD

ECB key weakness

Encrypts identical plaintext to identical cipher block texts.

CBC (Cipher Block Chaining)

Mode where each plaintext block is XORed with the previous ciphertext block, creating an avalanche chain. Older.

XOR

A way to combine 2 bits. Returns 1 if they're different, 0 if they are the same. The mixing tool.

Keystream

Output generated by an algorithm using a key.

Counter Mode (CTR)

Uses a different IV for each block, plus a counter (number). Most common today and is focused on speed.

What is the problem with Symmetric encryption

Scalability, due to the need of keys for both parties. Had to use Out-of-Band key options.

Implementation is

critical compared to mathematics alone for encryption.

S/MIME

Standard for public key encryption and digital signing of email.

Asymmetric Key bit sizes

1024, 2048, 4096

3DES

Symmetric, 64 block bits. 112 - 168 Key bits. 48 rounds

Key size

refers to the length of the encryption key, which determines the strength of the encryption itself.

Blowfish

Older symmetric block cipher with a 64-bit block size

Twofish

More modern design with a 128-bit block size, offering improved security and a strong alternative to AES.

DEREK

High speed encryption design optimized for cloud systems and scalability.

23BRAIDS

Lightweight encryption design for low power devices like IoT.

HSM (Hardware Security Module)

A cryptographic module that can generate cryptographic keys.

SPECK

light-weight block cipher designed by the NSA for IoT

SHA-1

Produces a 160-bit hash value and is used in DSS

Encryption technique that is based on factoring large prime numbers

RSA

Method for verifying the integrity of a message

Digital Signature

Perfect Forward Secrecy (PFS)

Past communications remain secure even if long-term keys are compromised.

Homomorphic Encryption

Encryption method that allows calculations to be performed on data without decrypting it first

Output Feedback (OFB)

Transforms a block cipher into a stream cipher

Benefit of using elliptic curve cryptography (ECC) over RSA?

Uses smaller keys for the same level of security

Elliptic Curve Cryptography (ECC)

Algorithm that uses mathematical operations on elliptic curves to generate secure keys, offering strong security with smaller key sizes. Good for blockchain technologies like bitcoin.

Blockchain technologies

Systems that use hashing and digital signatures to securely record and verify data.

Which stream cipher is commonly used in Wi-Fi encryption under WPA2?

RC4, Stream Cipher commonly used in WEP and WPA

Which encryption method is most commonly used to encrypt individual files in modern OS's?

AES

In asymmetric cryptography, which key is used to decrypt a message thats been encrypted with the recipient's public key.

The recipient's private key

What is a nonce?

A number used once, typically with cryptography.

Which algorithm supports homomorphic encryption?

RSA

Stream Cipher used in WEP, WPA, and WPA2?

RC4

Main purpose of the modulus operator (mod) in cryptography?

Returns the remainder and keeps numbers within a fixed range

Which protocols uses symmetric encryption to secure communication between two parties?

TLS, SSL, and IPsec with session keys being negotiated through asymmetric methods.

Dictionary Attack

Tries a list of commonly known passwords

Brute Force

To try every possible combination of characters until the correct password is found.

What does logarithms mean

Think of exponents. Find the exponent to get a number

What does Mod mean

Divide the first number by the second; the remainder is the result of mod.

Rule for SHA bit sizes

Number after SHA indicates the bits amount, except for SHA-1

Ephemeral Key

A temporary key that is used only once before it is discarded.

Collision attack

An attack where an attacker finds 2 different inputs that produce the same hash value.

Replay Attack

An attack where an attacker captures a valid message and retransmits it, making it seem like you.

Cipher Feedback (CFB)

Block cipher mode where each ciphertext depends on the previous ciphertext to encrypt or decrypt the next part. Also a weakness.

Playfair Cipher

Substitution cipher that encrypts pairs of letters (digraphs) using a 5x5 grid

Permutation

Rearrange positions.

Key Exhaustion Attack

Involves trying all possible keys to discover the correct one, often exploiting weaknesses in the key generation process.

Modular Arithmetic in cryptographic algorithms?

Performing calculations within a finite set of numbers

How is lattice based cryptography applied in modern encryption?

Uses geometric structures (grid) for cryptographic algorithms.

Which role do large prime numbers play in cryptographic algorithms

Ensure

What is a cryptosystem?

Nonrepudiation

Types of homomorphic encryption?

AHE, FHE, SHE, SHE? (need to check)

Stream ciphers use which type of key?

Symmetric, therefore they use both the same key for encryption and decryption.

What distinguishes CBC mode in a cryptographic system?

Which term refers to the blocks in a blockchain containing cryptographic proof of work?