Cryptography Basics - Advanced KB

Cryptography Basics: Securing Information in the Digital Age

Cryptography is the art and science of secure communication, especially in the presence of adversaries. It involves techniques that ensure data confidentiality, integrity, authentication, and non-repudiation.

The Core Goals of Cryptography

Confidentiality: Ensuring that information is accessible only to authorized individuals.
Integrity: Guaranteeing that information has not been altered in transit or storage.
Authentication: Verifying the identity of a sender or recipient.
Non-repudiation: Preventing a sender from denying that they sent a message.

Symmetric vs. Asymmetric Encryption

Symmetric Encryption

Also known as secret-key cryptography, symmetric encryption uses a single key for both encryption and decryption. This key must be securely shared between the sender and receiver.

Pros: Fast, efficient for large amounts of data.
Cons: Key distribution problem – securely sharing the key can be challenging.

Common algorithms include:

AES (Advanced Encryption Standard)
DES (Data Encryption Standard) - largely considered insecure now
3DES (Triple DES)

Example Scenario: Two individuals who already trust each other and have a secure way to exchange a secret key can use symmetric encryption for fast, private communication.

Asymmetric Encryption

Also known as public-key cryptography, asymmetric encryption uses a pair of keys: a public key and a private key. The public key can be shared with anyone, while the private key must be kept secret.

Pros: Solves the key distribution problem, enables digital signatures.
Cons: Slower and more computationally intensive than symmetric encryption.

Common algorithms include:

RSA (Rivest–Shamir–Adleman)
ECC (Elliptic Curve Cryptography)

How it works:

Sender encrypts a message using the recipient's public key.
Only the recipient's corresponding private key can decrypt the message.
For digital signatures, the sender encrypts a hash of the message with their private key. Anyone can verify this signature using the sender's public key.

Hashing Functions

A cryptographic hash function is a mathematical algorithm that maps data of arbitrary size to data of a fixed size, called a hash value, hash code, digest, or simply hash. It is designed to be a one-way function, meaning it's computationally infeasible to reverse the process (i.e., to find the original data from its hash).

Key Properties:

Pre-image resistance: Difficult to find the original message given the hash.
Second pre-image resistance: Difficult to find a different message that produces the same hash as a given message.
Collision resistance: Difficult to find two different messages that produce the same hash.

Common algorithms include:

MD5 (Message-Digest Algorithm 5) - considered cryptographically broken
SHA-1 (Secure Hash Algorithm 1) - also considered weak
SHA-256, SHA-384, SHA-512 (from the SHA-2 family)
SHA-3

Use Cases: Verifying data integrity, password storage, digital signatures.

Example of Hashing (Conceptual)

                    
                    // Imagine a function like this:
                    function hash(message) {
                      // Complex mathematical operations...
                      return hash_value;
                    }

                    let message1 = "Hello, world!";
                    let hash1 = hash(message1); // e.g., "a1b2c3d4e5f6..."

                    let message2 = "Hello, world."; // Notice the period
                    let hash2 = hash(message2); // e.g., "x9y8z7w6v5u4..."

                    console.log("Hash of '" + message1 + "': " + hash1);
                    console.log("Hash of '" + message2 + "': " + hash2);
                    // hash1 and hash2 will be drastically different,
                    // even for a tiny change in the input message.
                    
                

Digital Signatures

Digital signatures use asymmetric cryptography to provide authentication and integrity. They work by encrypting a hash of the message with the sender's private key. The recipient can then decrypt the hash using the sender's public key and compare it to a hash of the received message. If they match, the signature is valid.

Key Exchange Protocols

These protocols allow two parties to establish a shared secret key over an insecure channel, typically using asymmetric cryptography. The most famous example is the Diffie-Hellman key exchange.

Common Cryptographic Applications

SSL/TLS: Securing web traffic (HTTPS).
VPNs (Virtual Private Networks): Encrypting internet traffic for privacy and security.
Password Storage: Hashing passwords before storing them.
Digital Certificates: Verifying the identity of websites and individuals.
Cryptocurrencies: Used extensively for transaction security and identity.

Understanding these fundamental concepts is crucial for anyone involved in cybersecurity, software development, or protecting sensitive information in today's interconnected world.