Introduction to Cryptography

Introduction to Cryptography

• Cryptography originated from the Greek words "kryptos" (hidden or secret) and "graphy" (writing), meaning writing secretly
• It is the science of encrypting and decrypting information to prevent unauthorized access
• Codes and ciphers are created to transform readable data into an unreadable format, accessible only to authorized parties
• Cryptography allows secure storage and transmission of data between willing parties
• It combines math, computer science, and information security for secure communication
• Cryptography is essential for protecting sensitive data in various applications, including online banking, secure communications, and data integrity

Primary Goals/Principles of Cryptography

• Non-repudiation prevents any party from denying the authenticity of their signature or message
• Non-repudiation is a mechanism to prove that the sender actually sent the message
• Confidentiality ensures information accessibility is restricted to authorized individuals
• Authentication verifies the identity of parties involved in communication

Integrity

• Integrity, or anti-tampering, guarantees information accuracy and unaltered state during transmission

Cryptosystem and Related Terminologies

• Plaintext (or cleartext) is simple text easily perceived by a human and readable data
• Encryption uses mathematical algorithms to disguise sensitive information in plaintext
• Ciphers are a series of well-defined steps used to make the secret message actually unbreakable
• Keys are unique to the algorithm, necessary to make the algorithm and message work
• Decryption converts ciphertext back to plaintext

Cryptology

• Cryptology is the branch of math dealing with hiding and decoding secret messages

Two Sub-Branches of Cryptology

• Cryptography deals with hiding the data and making communication secure and confidential
• Cryptanalysis involves decryption, analysis, and breaking of secure information and studying and the process of analyzing and decrypting

Using Ciphers/Codes

• Techniques involve deciphering ciphers, codes, and encrypted text without the real key
• Technique of assessing a communication's plain text content without decryption key access
• A Cryptographer someone who creates encryption code used in cybersecurity
• A Cryptanalyst is someone who tries to crack encryption codes, also known as attackers

Who Uses Cryptanalysis?

• Hackers use cryptanalysis to find cryptosystem vulnerabilities, rather than brute force attacks
• Governments use cryptanalysis to decipher other nations' encrypted messages
• Companies specializing in cybersecurity use it to assess product security
• Academic researchers look for weaknesses in cryptographic algorithms and protocols

Cryptanalyst Duties

• Design security systems to prevent vulnerabilities
• Protect critical sensitive information from intercepting, copying, altering, or deleting
• Vulnerability evaluation, analysis, and targeting in an organization's cryptographic systems and algorithms
• Security measures involve searching for weaknesses in communication lines
• Test computational models for accuracy and reliability
• Develop statistical and mathematical models that analyze data and resolve security issues
• Staying current on new cryptology and data encryption methods
• Ensures that financial data is encrypted and only authorized users can access it
• Message transmission data is protected from hacking or changes in transit

Cryptanalysis: Attacking Cryptosystems

• Classical attacks include mathematical analysis and brute-force attacks
• Implementation attacks attempt to extract keys through reverse engineering or power measurement of devices like banking smart cards
• Social engineering tricks users into revealing passwords

History of Cryptography

• Started around 2000 B.C., Egyptians using hieroglyphs (sacred carving) to communicate important information
• Hieroglyphs involved intricate designs and symbols decipherable to knowledgeable few
• 2000 B.C. cryptography was engraved in stone

Other Historical Factual Points

• The Spartan military were known to use ciphers
• Spartans used steganography, which hides the existence of a message for secrecy
• The first known example of steganography was a hidden message tattooed on a messenger’s shaved head.
• Germans used electromechanical Enigma machine to encrypt messages in World War II
• Alan Turing introduced a code-breaking machine, the foundation for modern computers
• Kamasutra Cipher is an early substitution method from around 400 BC to teach women how to hide messages
• Randomly pairing letters for substitution was the main objective in ancient cryptography to introduce secrecy
• Modern ciphers provide integrity checking, identity confirmation, and digital signatures, and secure computations with confidentiality

Timeline

• BCE: Spartans use scytale, Egyptians develop hieroglyphic writing, and Roman ciphers like Caesar cipher emerge
• 1-1799: Leon Battista Alberti invents the first mechanical cipher machine, polyalphabetic cipher
• 1800-1899: Joseph Henry builds electric. Charles Babbage broke Vigenère’s autokey cipher
• 1900-1949: First break of German Army Enigma by Marian Rejewski in Poland
• 1950-1999: Charles Bennett and Gilles Brassard design the first quantum cryptography protocol, BB84
• 2000 to present: Microsoft and its allies vowed to end "full disclosure" of security vulnerabilities by replacing it with "responsible” disclosure guidelines

Encryption Methods

• Julius Caesar utilized the Caesar Cipher to encrypt military communications
• The scytale: Spartan tool for transposition cipher
• Vigenère Cipher employed polyalphabetic substitution
• Arab Cryptanalysis: Al-Kindi’s work on frequency analysis
• Renaissance: Leon Battista Alberti developed polyalphabetic cipher disk
• Renaissance: Giovanni Battista della Porta improved cipher techniques

18th-19th Century Ciphers

• Thomas Jefferson created the Jefferson disk cipher
• Charles Babbage broke the Vigenère cipher

World war II Ciphers

• Enigma Machine was used by Nazi Germany and cracked by Alan Turing
• The Purple Cipher was used by Japan and decrypted by U.S. cryptanalysts

Modern Ciphers

• Data Encryption Standard (DES) adopted in 1977
• The RSA Algorithm introduced public-key cryptography in 1978
• Advanced Encryption Standard (AES) adopted in 2001

21st Century Ciphers

• Quantum Cryptography is an emerging field leveraging quantum mechanics
• Blockchain and Cryptocurrencies use cryptographic techniques for secure transactions

Types of Cryptography

• Homomorphic encryption allows computations on encrypted data and has significant implications for privacy
• Symmetric cryptography uses the same key for encryption and decryption, efficient for large data processing but requires secure key distribution and Advanced Encryption Standard (AES) and Data Encryption Standard (DES)
• Digital Signatures provide message authentication and integrity using asymmetric cryptography
• Asymmetric Cryptography (public-key) cryptography, a pair of keys for secure communication; a public key for encryption and a private key for decryption like RSA and ECC
• Hash Functions produce fixed sized strings from input data for integrity which includes SHA-256 and MD5

Terminologies

• Plaintext is the original, readable message or data
• Ciphertext is the encrypted message or data, unreadable without decryption
• Encryption is the process of converting plaintext into ciphertext
• Decryption is the process of converting ciphertext back into plaintext
• A cipher is an algorithm for performing encryption or decryption
• A key is a piece of information used in a cipher to encrypt or decrypt data

Additional Terminology

• Symmetric Key Cryptography uses the same key for both encryption and decryption
• Asymmetric Key Cryptography uses a pair of public and private keys for encryption and decryption
• A Public Key is shared openly and used for encryption
• A Private Key is kept secret and used for decryption
• A Hash Function converts data into a fixed-size string (hash value)
• A Digital Signature verifies the authenticity and integrity of a message or document
• A Certificate Authority (CA) issues digital certificates to verify entities' identities
• Cryptanalysis is the study of analyzing and breaking cryptographic systems
• Cryptographic Protocol is a sequence of operations that ensure secure communication
• A Nonce is a random/unique value used only once to prevent replay attacks
• Salt is random data added to passwords before hashing

Types of Values

• Initialization Vector (IV) is random value used with a key for unique encryption
• Elliptic Curve Cryptography (ECC) is a public-key cryptography based on elliptic curves' algebraic structure
• Zero-Knowledge Proof is a method to prove knowledge of a value without revealing it
• Diffie-Hellman Key Exchange is a method for securely exchanging cryptographic keys
• A Man-in-the-Middle Attack: an attack where an attacker intercepts and alters communication
• Brute Force Attack tries all combinations to crack a key/password
• Side-Channel Attack gains information on the implementation of a cryptosystem
• Public Key Infrastructure (PKI) is a framework for managing digital keys, certificates
• Steganography is hiding messages within other non-secret text
• Block Cipher encrypts data in fixed-size blocks e.g AES
• Stream Cipher encrypts data as a stream of bits/bytes e.g., RC4)

Encryption Methods Continued

• Key Exchange: Is sharing cryptographic keys between parties
• Key Management: Is handling/protecting cryptographic keys
• Message Authentication Code (MAC): used to authenticate a message and ensure integrity
• Padding: adding data to plaintext to fit block size for encryption
• Perfect Forward Secrecy (PFS): ensures future session keys won't be compromised
• Quantum Key Distribution (QKD): uses quantum mechanics to securely distribute keys
• Rainbow Table: A table used to reverse cryptographic hash functions
• Replay Attack: Where a data transmission is maliciously repeated
• Secure Multiparty Computation (SMPC): jointly computes a function while keeping inputs private
• Symmetric Encryption: Encryption where the same is key is used for both encryption and decryption

Classical Caesar Cipher

• Caesar Cipher is a simple substitution or rotation encryption
• Each letter is replaced by a letter some fixed positions down the alphabet
• Julius Caesar used it around 58 BC for military messaging
• If intercepted, a substitution makes it readable
• “Caesar Box” or “Caesar Cipher" one of the earliest, sent secret messages to his generals
• Julius Caesar: Named himself Roman dictator and was assassinated in 44 BCE
• The formula of encryption is: En (x) = (x + n) mod 26
• The formula of decryption is: Dn (x) = (xi - n) mod 26

Caesar Advantages

• Easy to implement and use so it is suitable for beginners
• It can be physically implemented; such as rotating disks or sets
• It requires only a small set of pre-shared information
• It can be modified to create a more secure variant

Caesar Disadvantages

• Not secure against modern decryption methods
• Not suitable for long text due to difficulty cracking
• Not suitable for secure communication because it is easily broken
• Does not provide confidentiality, integrity and authenticity in a message
• Vulnerable to brute force and Known-plaintext attacks

Cipher Laws

• Data Privacy Act of 2012: Regulates personal data collection, storage, use, and processing in the Philippines, including encryption
• Republic Act No. 8792 (Electronic Commerce Act of 2000): Regulates electronic commerce, including digital signatures, and recognizes the importance of encryption
• Republic Act No. 10175 (Cybercrime Prevention Act of 2012): Regulates computer-related offenses like hacking and unauthorized access
• Anti-Money Laundering Law (Republic Act No. 9160): regulates transactions with encryption an encryption component
• NPC Guidelines focuses on data privacy and security and the use of encryption, and it emphasizes organization responsibility to employ tech and provide transparency

Importance of Laws (Cryptography)

• Ensure information privacy/security and regulate cryptographic techniques use, promote responsible cryptography and address its misuse

Vernam Cipher

• Is the first cryptographic mechanism to achieve perfect secrecy
• Invented in 1917 by Gilbert Vernam at American Telephone & Telegraph Company (AT&T)
• They are the basis for one time pads (OTP) by Joseph Mauborgne
• Original Vernam used binary/XOR on bits

Key Concepts (Cipher)

• Symmetric key cryptography
• Modular arithmetic (base 10)
• Perfect secrecy and ASCII character encoding

Encryption and Decryption Processes

• Text to Decimal: Convert each character to 3-digit ASCII
• Generate Key: Create random digits matching plaintext
• Encrypt: Digit-wise subtraction (mod 10)
• Receive Ciphertext: Encrypted numeric string
• Decrypt: Digit-wise addition (mod 10)
• Decimal to Text: Convert 3-digit groups back to

Vigenère Cipher

• Polyalphabetic substitution used for data encryption
• Original plaintext is concealed using polyalphabetic
• Invented by Giovan Battista Bellaso in 1553
• Mistakenly attributed to Blaise de Vigenère (1586)
• Referred to as “le chiffre indéchiffrable" (the unbreakable cipher)
• Remained secure until Charles Babbage developed successful cryptanalysis methods in the 19th century
• Use a keyword to determine shift values and it was considered secure for 300+ years
• Strengths/resistant to frequency analysis, it encrypts using long keys
• Multiple ciphertext letters represent same plaintext letter

Weaknesses and Encryption

• Repeating key patterns (kasiski examination attacks)
• itis Vulnerable to known-plaintext attacks _ Block cipher: symmetric method that processes plaintext data into equal length ciphertext blocks
• Characteristics: encrypts fixed size blocks with complex transformation rounds
• Is resistant to bit-flipping attacks
• Common Modes which includes ECB, CBC, CFB, CTR
• Examples = AES, DES, 3DES, Blowfish etc
• Stream Cipher- encryption that operates on a continuous stream of data
• Characteristics: encrypts individual bits/bytes and creates a pseudorandom keystream
• Types:
• Stream Cipher
• Synchronous and Self-synchronizing

Stream Ciphers and Public Encryption

• Examples are RC4, Salsa20, ChaCha20
• Operation Process = Initialize with key and nonce, combine PRNG ,Output ciphertext stream
• Initialize with nonce an key, combine plaintext, and output
• Block Ciphers process with fixed size while stream ciphers use a simple XOR/more memory
• Public cryptography uses higher memory
• Public key is used openly
• Private keys are kept a secret
• Public has strong data integrity protection and efficient for stream ciphers
• Private keys = resistant ot bit flipping and no paddings

Block Cipher

• ECB = repeated pattern, CBC, CBF, CTR with nonce processesing
• Is more efficient for smaller key sizes

Algorithms

• Key Algorithms: Diffie-Hellman, Digital Signatures, Key Exchange,
• Key algorithm is a system to secure and distribute keys and limit quanutum therats
• Keys are based on modular systems and elliptic curves
• DH = public-key cryptography algorithm
• allows 2 parties to securely the tablish shared secret over channel
• D and H allow two parties to agree on a shared secret, without revealing it to any
• a MIM-h attack where the attacker can infiltrae the actor and communication chain

D and H Advantages and Disadvantages

• Simple/fast/secure and easy to implement
• Vulnerable to man-in-the-middle attacks