Cryptography

What if we need that one-way transformation to be two-way, but only for some selected people or systems? That's where encryption comes into play.

Encryption transforms data or document into a form that can only be reversed by the use of a key. Whoever holds the key can access the data. If someone tries to open it without the key, they will only see gibberish.

Introduction to Cryptography

Cryptography is the practice of securing data and communication in the presence of adversaries. In system design, cryptography ensures that data remains confidential, authentic, and untampered, even when systems operate over untrusted networks.

Modern systems rely on cryptography to protect user data, secure communication between services, and establish trust between distributed components.

Security Goals of Cryptography

Cryptographic systems are designed to achieve the following core goals:

• Confidentiality – Only authorized parties can read the data
• Integrity – Data cannot be altered without detection
• Authentication – Verifying the identity of entities
• Non-repudiation – Preventing denial of performed actions

A secure system typically combines multiple cryptographic techniques to achieve these goals.

Encryption Fundamental

Encryption transforms readable data (plaintext) into unreadable data (ciphertext) using an algorithm and a key.

Key concepts:

• Plaintext
• Ciphertext
• Encryption algorithm
• Encryption key

Without the correct key, encrypted data is computationally infeasible to decrypt.

Symmetric Encryption

Symmetric encryption uses the same key for encryption and decryption.

Common algorithms:

• AES (Advanced Encryption Standard)
• DES (deprecated)
• 3DES (legacy)

Advantages:

• Fast and efficient
• Suitable for larger data volumes

Challenges:

• Secure key distribution
• Key rotation and management

Use cases:

• Data at rest
• Internal service communication

Asymmetric Encryption

Asymmetric encryption uses a pair of keys:

• Public key (shared)
• Private key (kept secret)

Common algorithms:

• RSA
• Elliptic Curve Cryptographic (ECC)

Advantages:

• Secure key exchange
• Enables digital signatures

Disadvantages:

• Slower than symmetric encryption

Use cases:

• Key exchange
• Secure authentication
• TLS handshakes

Hybrid Encryption

Most real-world systems use hybrid encryption:

• Asymmetric encryption for key exchange
• Symmetric encryption for data transfer

This approach combines security with performance.