Cryptography Basics

• Cryptography
• Obfuscation
  • Data Masking or Obfuscation
  • Steganography
  • Tokenization
  • Diffusion
  • Confusion
• Types of Encryption
  • Symmetric Encryption
  • Asymmetric Encryption
  • Hybrid Implementation
• Storing Keys
• Ciphers
  • Stream Ciphers
  • Block Ciphers
• Common Ciphers
  • Cease Cipher
  • Vigenere Cipher
  • Exlusive OR XOR

Cryptography

The science and practice of securing communication and information through encoding, ensuring only authorized parties can access it. Its purpose is to protect data integrity, confidentiality, and authenticity.

• Encryption
  • Transforming plaintext into ciphertext using an algorithm and a key.
• Decryption
  • Converting ciphertext back to plaintext with the appropriate key.

Obfuscation

Data Masking or Obfuscation

Obfuscation is a technique to make code, data, or communications harder to understand or analyze.

• Protect intellectual property, sensitive information.
• Protect sensitive data from being easily understood or extracted.
• Prevent unauthorized reverse engineering or tampering with software.

How It Works

• Code or data is transformed into a form that is functionally equivalent but difficult for humans to read or interpret.
• Common methods include:
  • renaming variables and functions with meaningless names
  • removing comments
  • reordering code structures.

Considerations

• Obfuscation is not foolproof.
• Skilled attackers can often reverse-engineer obfuscated code.
• Over-obfuscation can complicate legitimate debugging and maintenance.
• Not a replacement for proper encryption and other security practices.

Steganography

Steganography and obfuscation are techniques used to conceal information, but they differ in their methods and objectives.

• Steganography hides a message within another medium to keep its existence secret.
• Obfuscation makes code or information difficult to understand

Derived from Greek word, meaning “covered writing”, Steganography hides secret data within ordinary, non-secret files or messages. Its purpose is not to prevent unauthorized access, but to avoid suspicions.

We can try this at Steganography Online.. We’ll use the sample photo below:

The message that we want to hide in the image:

All right men, commence Operation: Special Delivery! 

Upload the photo and enter the message in the field. Click Encode.

It will generate the encoded image.

Right-click on the third image > Save as. Then check the properties of the original photo and the encoded photo. We can see that the size changed.

Tokenization

Tokenization replaces sensitive information with non-sensitive tokens, enhancing data security by removing direct exposure to confidential data.

How It Works

• Sensitive data is swapped for unique tokens stored in a secure token vault.
• The original data is stored somewehere.
• The original data can only be retrieved through secure processes with proper access.
• If data breach occurs, attackers will only find the useless tokens.

Applications

• Used in payment systems for credit card security.
• Applied in healthcare to protect patient information.
• Employed in databases to secure sensitive data.
• Supports compliance with data protection regulations.

Considerations

• The token vault must be securely protected.
• Tokenization should be part of a comprehensive security strategy.

Diffusion

Diffusion spreads the effect of a single input across many output elements, thus obscuring patterns.

• Makes the information less visible, less obvious.
• In block ciphers, diffusion is achieved through operations like permutations and mixing.
• Example is blurring an image.

Confusion

Confusion creates complex relationships between the key and ciphertext, making it difficult to infer the key.

• Changing a property of the data and make it more difficult to interpret, more unintelligible.
• Confusion works alongside diffusion to create robust encryption schemes.
• Example is scrambling or changing the pixels of an image.

Types of Encryption

These types of encryption play critical roles in modern cybersecurity, often used together to achieve a balance of speed and security.

Symmetric Encryption

Symmetric cryptography uses the same key for both encryption and decryption. The sender and receiver must share this key, keeping it secret from others.

• Session key - single key is used to encrypt and decrypt data.
• Both parties must have this key.

Symmetric encryption is generally faster and less computationally intensive compared to asymmetric cryptography. It is also effective for encrypting large volumes of data.

Sending the key:

• In-band
  • Sending the key along with the encrypted data
  • Risky, vulnerable to sniffing
• Out-of-band
  • Providing the key separately from the encrypted data
  • Can be provided beforehand or via phone/SMS

Disadvantages:

• Key distribution and management can be challenging
• If the key is compromised, the entire system is at risk.

Use Cases:

• Secure communication within closed networks
• Encrypting files or databases
• Securing backups.

Asymmetric Encryption

Asymmetric cryptography uses a pair of keys:

• a public key for encryption
• a private key for decryption.

The public key can be shared openly, but the private key must remain confidential.

• **Public key encrypts data**, and only the corresponding private key can decrypt it.
• **Private key decrypts the data**, can be used to sign data, which the public key can verify.

Example Algorithms:

• RSA (Rivest-Shamir-Adleman)
• ECC (Elliptic Curve Cryptography)
• DSA (Digital Signature Algorithm).

Advantages:

• No need to share the private key, reducing the risk of key compromise.
• Allows for digital signatures and public key infrastructure (PKI).

Disadvantages:

• Slower and more resource-intensive than symmetric cryptography.
• Less efficient for large amounts of data.

Use Cases:

• Secure communication over public networks, digital signatures, certificate authorities, and secure key exchange.

Hybrid Implementation

Utilizes asymmetric encryption to securely transfer a private key, which can then be used with symmetric encryption.

Storing Keys

Best practices:

• Store keys in secure hardwared modules
• Encrypt keys when at rest
• Transmit keys securely when used
• Limit key access to regular audits and monitoring

Ciphers

A cipher is an algorithm used to encrypt and decrypt information, transforming plain text into coded (cipher) text and vice versa.

• Ciphers ensure data confidentiality
• Central to encryption protocols.

Types of Ciphers:

• Stream Cipher
• Block Cipher

Stream Ciphers

Stream Ciphers encrypt data bit by bit or byte by byte in a continuous stream.

• Performs encryption on **single byte at a time.**
• Uses a key stream generator to create a pseudo-random sequence of bits (the key stream).
• The key stream is then XORed with the plaintext to produce ciphertext.

Common Features:

• **Uses same key for encryption and decryption.**
• Implemented mostly on **hardware-based solutions**
• Often used in **real-time applications** where data is continuously transmitted (e.g., streaming services).
• Vulnerable to certain types of attacks if key stream is reused or not sufficiently random.

Examples:

• RC4
• Salsa20
• ChaCha20

Block Ciphers

Block Ciphers break the input into fixed-size blocks (e.g., 64-bit or 128-bit) and performs the encryption on each block.

• Performs encryption on **per block basis.**
• A block of plaintext is processed with a key to produce a block of ciphertext.
• Multiple rounds of transformation can also be used (e.g., substitution and permutation).

Common Features:

• **Easier to implement, less susceptible to security problems.**
• Implemented mostly on **software solutions**
• Often used in protocols and file encryption, where data is processed in chunks.
• Require padding when the plaintext doesn’t evenly divide into block sizes.
• Can be operated in various modes to enhance security or support specific applications.

Examples:

• AES
• DES
• 3DES

Common Ciphers

Cease Cipher

Named after Julius Caesar, it is a simple substitution cipher where each letter in the plaintext is shifted a certain number of positions down or up the alphabet.

• Shifts each letter in the plaintext a certain number of positions along the alphabet.
• The number of positions to shift, typically between 1 and 25.
• Example: With a shift of 3, ‘A’ becomes ‘D’, ‘B’ becomes ‘E’, and so on.
• ROT2 - two shifts in positions
• ROT3 - three shifts in positions, and so on.

Although it’s historically significant, the Caesar Cipher is not used for serious encryption today due to its simplicity and vulnerability to straightforward cryptanalysis

Vigenere Cipher

The Vigenère Cipher is a type of polyalphabetic substitution cipher that uses a repeating key phrase to determine shifting patterns for each letter in the plaintext, offering greater security than simple substitution ciphers.

• A key phrase, repeated to match the plaintext length, determines the shift for each letter.
• To decrypt, use the same key to reverse the shifts and recover the plaintext.

Strengths:

• Provides increased complexity, making frequency analysis and brute-force attacks more difficult.

Weaknesses:

• Susceptible to Kasiski examination and Friedman tests, which can reveal key patterns and lengths, leading to cryptanalysis.

Example:

• With the key “LEMON,” the plaintext “HELLO” is encrypted by shifting each letter according to the corresponding letter in the key, resulting in “OIWWC.”

Exlusive OR (XOR)

Exclusive OR (XOR) is a binary operation used extensively in cybersecurity and cryptography. It operates on bits, returning 1 if the bits are different and 0 if they are the same. Here’s a concise description with key bullet points:

• XOR compares two bits; if they’re different, it outputs 1; if they’re the same, it outputs 0.
• XOR is reversible, allowing data encrypted with a key to be decrypted by XORing again with the same key.

Applications:

• Encryption:
  • Commonly used in stream ciphers and some block ciphers to combine plaintext with a key stream, creating ciphertext.
• One-Time Pad (OTP):
  • A theoretically unbreakable encryption method that uses XOR with a key as long as the plaintext, provided the key is truly random and never reused.
• Data Manipulation:
  • XOR can be used to toggle bits or swap values without additional storage.
• Error Detection/Correction:
  • In parity checks and error-correcting codes, XOR helps identify errors in transmitted or stored data.

Security Considerations:

• Key Management:
  • Security in XOR-based encryption relies heavily on key secrecy and randomness.
• Vulnerabilities:
  • If the key is reused or predictable, XOR-based encryption is susceptible to various attacks, including known-plaintext attacks.

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