Cryptography and Encryption Techniques Quiz

Modern Symmetric Encryption Methods

• Modern encryption systems use principles of substitution and permutations to encrypt data efficiently.
• Basic operations like XOR, substitutions, and permutations are fundamental to modern encryption methods.
• Symmetrical encryption methods use the same key both to encrypt and decrypt data.
• Classical encryption methods, such as the Enigma machine, provide the basis for modern symmetrical encryption methods.

Modern Encryption Methods

• Classical encryption methods, including the Enigma machine, are based on substitution operations.
• A basic unit of data (like a letter) is substituted for another, as determined by rules and a key (KE).
• Each substitution is a 1:1 mapping between possible characters in plaintext (pt) and ciphertext (ct).
• Substitutions can be fixed (mono-alphabetic) or change over time (poly-alphabetic).

Letter/byte substitutions for digital data - XOR

• XOR is equivalent to Caesar’s cipher for digital systems and is a common operation for combining bits or bytes of plaintext and key.
• In digital systems, the basic unit of data is a bit, often grouped into bytes.
• The XOR operation is reversible by applying another XOR.

Substitution Boxes (S-Boxes)

• S-Boxes are used to substitute bits or bytes of data, and are often used in lookup tables to enhance security against linear analysis.
• S-boxes do not depend on the key, and can be fixed or generated from the key before encryption begins.
• The S-Boxes typically operate on single bytes.
• Multiple 1-byte S-Boxes can be used in parallel to encrypt more than one byte of data simultaneously.

Permutation Boxes (P-Boxes)

• P-Boxes mix the results of the separate substitutions performed by S-boxes.
• P-Boxes aim to distribute the outputs of the S-Boxes across other S-Boxes.
• S-boxes and P-boxes are used together to effectively spread the influence of a change in one input over a larger area of the output, protecting against linear and differential cryptanalysis.

Block Ciphers

• Block encryption algorithms use a series of operations on fixed-size blocks of data.
• If the message is longer than the block size, it's split into multiple blocks for separate encryption.
• Each block is processed by a block encryption algorithm, and smaller blocks are padded as needed.
• The keysize is usually the same as or similar to the block size.

Example Block Encryption Algorithm - AES

• AES (Advanced Encryption Standard) is a commonly used block cipher.
• AES uses rounds, which are basic encryption steps performed multiple times.
• The key is expanded into multiple round keys, during each round, there are operations on bits and bytes.
• Decryption process is similar but with inverse operations.

Block Ciphers - ECB Mode

• ECB (Electronic Codebook Mode) encrypts each block independently in a straightforward manner.
• A significant drawback is that identical plaintext blocks produce identical ciphertext blocks, making patterns in the original data visible in the encrypted result.
• ECB mode is extremely vulnerable to known-plaintext attacks.

Block Ciphers - CBC Mode

• CBC (Cipher Block Chaining) mode XORs each plaintext block with the previous ciphertext block before encryption.
• This prevents identical plaintext blocks from producing identical ciphertext blocks, making it more secure than ECB for most applications.
• The initialization vector (IV) is used for the first plaintext block to provide a different start point.

Block Ciphers - CTR Mode

• CTR (Counter Mode) generates a unique, non-random key stream for each block.
• Each block of plaintext XOR'd with the respective key stream, and encrypted/decrypted independently.
• CTR mode is highly efficient for parallel processing.

Stream Ciphers

• Stream ciphers operate on data streams (like communication channels) rather than blocks.
• Stream ciphers use a key stream generated by a pseudorandom number generator, then XOR'ing with input data.
• Stream ciphers are generally much faster than block ciphers, as they operate on data bit-by-bit.

Synchronised Stream Ciphers

• Synchronised stream ciphers require both sender and receiver to use the same key stream.
• Employ a pseudo-random binary number generator (PRBNG).
• The aim is for the keys generated to be unpredictable to outsiders to provide security.

Secure Wifi

• WEP (Wired Equivalent Privacy) and TKIP used stream ciphers like RC4, were later superseded by AES-based methods.
• Current Wifi security standards provide much greater security through more sophisticated methods.

Example: DVD Encryption

• DVD encryption systems, like CSS, employed stream ciphers but were quickly cracked due to weak cipher designs, and small keysizes, and cryptanalysis methods.
• Stronger and more secure methods are required to protect data effectively now.

Message Authentication

• Cryptographic hash functions are used to create unique "fingerprints" of messages.
• Hash functions can verify if a message has been changed in transit without revealing the original message.
• The recipient can use the same hash key to create a checksum to confirm the identity of the message provider.

Cryptographic Hashes

• Hash functions produce a unique "fingerprint" of data, used for verification.
• Common hash functions include SHA-1, MD5, SHA-256.
• Hashing is essential for verifying that data hasn't been tampered with during transmission or storage.

Cryptographic Hashes for Password Storage

• Secure password storage requires hashing, not storing passwords in plain text.
• Common algorithms use Bcrypt or Scrypt to obfuscate passwords and slow down brute force attacks.
• Salts are appended to passwords before hashing to avoid rainbow-table vulnerabilities, which are pre-calculated hashed of common passwords.

Brute-force and other methods for obtaining passwords

• Brute-force attacks try all possible password combinations to guess accounts.
• Reused passwords across multiple platforms increase susceptibility to breaches.
• Modern password hashing techniques make brute-force attacks very slow and computationally costly.

Message Authentication Codes (MACs)

• MACs provide message authentication and integrity.
• MACs use a shared secret key to generate message authentication tags, ensuring only legitimate users can verify information.
• Attackers who intercept and change the message will be unable to generate a valid MAC if they don't share the key.

HashCash

• HashCash was an early method for controlling spam and requiring a "work-proof."
• The goal is to slow down the massive volume of spam, so that sending a spam email becomes more expensive for mail spammers.

Hashing in Block Chains / Cryptocurrency

• Blockchains use cryptographically secure hashing for data integrity, as part of the distributed ledger structure.
• Hashing techniques like SHA-256 are crucial in the verification of transactions and to ensure the integrity of the data.

Blockchains

• Blockchains are used to create a trustworthy record of transactions or events that are secure, immutable, and decentralized.
• Each block contains a hash of the previous block, creating a linked chain, making tampering difficult and instantly noticeable.
• They use cryptography and distributed ledger technology to establish trust across a network of participants.

Bitcoin

• Bitcoin uses blockchains to record and manage transactions.
• Block creation involves solving a cryptographic puzzle associated with a block's nonce.
• The Bitcoin network ensures the integrity of the history through a complex system of verification and validation, which includes cryptographically securing the transactions and ensuring the history of transactions is verifiable and trusted by all network participants.

Bitcoin - Proof-of-Work

• Bitcoin's proof-of-work system is inspired by HashCash, and associates costs with block creation.
• Blocks contain a nonce that affects the hash value; the difficulty target decreases over time.
• Bitcoin ensures ownership through a verifiable and secure ledger, which is updated and distributed across the network.

Bitcoin - Block Structure & Transactions

• Bitcoin block data format includes details of Bitcoin transactions
• The process for creating and adding blocks to the chain is carefully controlled to prevent manipulation or unauthorized additions, maintaining the security of Bitcoin transactions and ownership.

Additional Notes

• Specific encryption modes like ECB, CBC, CTR affect how blocks are processed and can have security implications when using them with different types of data (like images).
• Hashing techniques are fundamental to many cryptographic applications, ensuring data integrity and non-repudiation (preventing the denial of having performed an action.)
• The concepts presented highlight some of the considerations that surround the implementation of secure systems in many areas, such as computing, cryptocurrency, and networking.

Test your knowledge on various cryptography concepts, particularly focusing on block ciphers, stream ciphers, and password storage techniques. This quiz covers the advantages and disadvantages of different encryption methods, specifically CTR mode, and explores hashing algorithms used for secure password management.