Cryptography Guide

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Basic Cryptography Terms and Concepts ​

Core Concepts ​

Cryptography ​

The science and practice of securing communication and information through encoding messages or information in such a way that only authorized parties can access it.

Encryption ​

The process of converting plaintext (readable data) into ciphertext (scrambled data) using an algorithm and key.

  • Example: Converting "HELLO" to "KHOOR" using a simple shift cipher

Decryption ​

The reverse process of encryption, converting ciphertext back into plaintext using the appropriate key.

  • Example: Converting "KHOOR" back to "HELLO"

Cipher ​

An algorithm for performing encryption or decryption.

  • Classical ciphers: Caesar, Vigenère, Substitution
  • Modern ciphers: AES, RSA, ChaCha20

Key ​

A piece of information (usually a string of bits or a number) that determines the output of a cryptographic algorithm.

  • Symmetric key: Same key for encryption and decryption
  • Public/private key pairs: Different keys for encryption and decryption

Types of Cryptography ​

Symmetric Cryptography ​

Uses the same key for both encryption and decryption.

  • Advantages: Fast, efficient
  • Disadvantages: Key distribution challenge
  • Examples: AES, DES, ChaCha20

Asymmetric Cryptography ​

Uses different keys for encryption (public key) and decryption (private key).

  • Advantages: Secure key exchange, digital signatures
  • Disadvantages: Slower than symmetric
  • Examples: RSA, ECC, DSA

Hash Functions ​

One-way functions that generate a fixed-size output from variable-size input.

  • Properties: Deterministic, preimage resistance
  • Uses: Password storage, data integrity
  • Examples: SHA-256, SHA-3, BLAKE2

Basic Terms ​

Plaintext ​

The original, readable message before encryption.

  • Also called: Cleartext
  • Example: "Meet me at noon"

Ciphertext ​

The encrypted, scrambled version of the plaintext.

  • Result of encryption process
  • Should appear random
  • Example: "Zrrg zr ng abba"

Protocol ​

A defined set of rules and procedures for cryptographic operations.

  • Example: TLS, SSH, Signal Protocol

Nonce ​

A number used only once in cryptographic operations.

  • Purpose: Prevent replay attacks
  • Also called: Initialization Vector (IV)
  • Should be unique for each encryption

Salt ​

Random data added to input before hashing.

  • Used in password hashing
  • Prevents rainbow table attacks
  • Unique per password

Security Concepts ​

Authentication ​

Verifying the identity of a user or system.

  • Methods: Passwords, certificates, biometrics
  • Protocols: OAuth, SAML
  • Multi-factor authentication (MFA)

Authorization ​

Determining what actions an authenticated user can perform.

  • Access control lists (ACL)
  • Role-based access control (RBAC)
  • Principle of least privilege

Integrity ​

Ensuring data hasn't been modified.

  • Message Authentication Codes (MAC)
  • Digital signatures
  • Hash functions

Non-repudiation ​

Preventing denial of having performed an action.

  • Digital signatures
  • Audit logs
  • Timestamps

Attack Types ​

Brute Force Attack ​

Trying every possible key or password.

  • Countermeasure: Long keys
  • Example: Trying all possible AES keys

Man-in-the-Middle (MITM) ​

Intercepting communication between two parties.

  • Attack vector: Unsecured networks
  • Prevention: Authentication, encryption
  • Example: Fake Wi-Fi hotspots

Dictionary Attack ​

Using a list of likely passwords.

  • Target: Password systems
  • Prevention: Strong passwords, salting
  • Example: Common password lists

Cryptographic Primitives ​

Random Number Generator (RNG) ​

Generates random numbers for cryptographic use.

  • Types: True Random, Pseudorandom
  • Uses: Key generation, nonces
  • Example: /dev/urandom

Key Derivation Function (KDF) ​

Derives one or more keys from a master key.

  • Uses: Password hashing
  • Examples: PBKDF2, Argon2
  • Properties: Slow, memory-hard

Message Authentication Code (MAC) ​

Provides message integrity and authentication.

  • Types: HMAC, CMAC
  • Uses: Verify message integrity
  • Example: HMAC-SHA256

Standards and Protocols ​

Transport Layer Security (TLS) ​

Secures internet communications.

  • Previously: SSL
  • Uses: HTTPS, secure email
  • Components: Handshake, record protocol

Digital Certificates ​

Electronic documents to prove identity.

  • Format: X.509
  • Contains: Public key, identity info
  • Issued by: Certificate Authorities (CA)

Zero-Knowledge Proof ​

Proves knowledge without revealing it.

  • Properties: Completeness, soundness
  • Uses: Authentication, privacy
  • Example: Password verification

Best Practices ​

Key Management ​

  • Regular key rotation
  • Secure key storage
  • Key backup procedures
  • Access control

Password Security ​

  • Minimum length requirements
  • Complexity rules
  • Regular changes
  • Secure storage (hashing)

Algorithm Selection ​

  • Use standard algorithms
  • Avoid outdated ciphers
  • Follow security recommendations
  • Regular updates

Common Tools ​

OpenSSL ​

  • Certificate management
  • Encryption/decryption
  • Key generation
  • Command-line interface

GPG (GNU Privacy Guard) ​

  • Email encryption
  • File encryption
  • Digital signatures
  • Key management

Password Managers ​

  • Secure password storage
  • Password generation
  • Encrypted vaults
  • Cross-platform sync

Resources for Learning ​

Documentation ​

  • RFCs (Request for Comments)
  • NIST publications
  • Academic papers
  • Vendor documentation

Practice Platforms ​

  • Cryptopals challenges
  • CTF competitions
  • Online coding platforms
  • Security labs

Communities ​

  • Security forums
  • Academic groups
  • Professional organizations
  • Online communities

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