What is encryption? From the Caesar cipher to modern information guardians of quantum security.

When you pay for a cup of coffee with your phone, send private messages in a chat app, or store work files in the cloud, an invisible guardian—encryption—operates behind the scenes. Derived from the Greek words "kryptós" (hidden) and "graphía" (writing), encryption is essentially the science of converting information into an unreadable form through mathematical algorithms, protecting data in untrusted environments. The National Institute of Standards and Technology (NIST) defines it as a discipline that embodies the principles, means, and methods of data transformation, with the core goal of preventing unauthorized use or alteration of sensitive information.

##Millennium Evolution: From Physical Steganography to Mathematical Labyrinth The history of encryption intertwines with human civilization:

• Classical Period (BC - late 19th century): The Chinese Western Zhou "Yin Fu" used bamboo strips of different lengths to convey military information (three inches = defeat, five inches = request for aid); the Roman Caesar cipher encrypted commands by shifting letters (e.g., a shift of 3: A→D); the ancient Greek Spartan stick (Scytale) achieved information concealment by winding parchment around a wooden stick.
• Mechanical Revolution (1900 - 1950): The Nazi ENIGMA cipher machine generated 10¹⁴ types of keys using rotor combinations, which was once considered "unbreakable" until Turing's team deciphered its encrypted messages with the "Colossus" computer, turning the tide of World War II.
• Modern Foundation (1949 to Present): In 1949, Shannon proposed the theories of diffusion (the plaintext affects multiple ciphertexts) and confusion (the relationship between ciphertext and key is complicated), pushing encryption towards mathematical formalization. In 1976, Diffie-Hellman pioneered the public key cryptosystem, solving the key distribution problem; the following year, the RSA Algorithm utilized the complexity of large number factorization, laying the cornerstone for asymmetric encryption.

##Five Core Objectives: Building the Pillars of Digital Trust Modern encryption achieves five layers of protection through technology:

1. Confidentiality: AES-256 encryption of bank card numbers to ensure that only authorized parties can read.
2. Integrity: SHA-3 hash value verifies whether the electronic contract has been tampered with during transmission.
3. Authentication: RSA digital certificates verify the authenticity of website servers, defending against phishing attacks.
4. Non-repudiation: ECDSA signatures ensure that the initiator of a Bitcoin transaction cannot deny it.
5. Availability: The design of anti-attack algorithms ensures the continuous availability of encryption services.

##Three Main Types of Technology: Symmetric, Asymmetric, and Hybrid Collaboration

• Symmetric encryption: Algorithms like AES and SM4 are fast single-key algorithms, suitable for large data encryption (such as full disk encryption), but key distribution requires a secure channel.
• Asymmetric encryption: RSA, ECC public key encryption and private key decryption, solving the pain point of key distribution, supporting the digital certificate system, but with a relatively large computational overhead.
• Hybrid System: The TLS 1.3 protocol uses RSA for key exchange during the handshake phase and AES for data transmission, balancing security and efficiency.

##Breakthroughs: Quantum Threats and the Lightweight Revolution In 2025, encryption is undergoing a dual evolution:

• The rise of post-quantum cryptography (PQC): In 2022, NIST standardized CRYSTALS-Kyber (based on lattice theory) to resist quantum computing attacks. In August 2025, the EdDSA signature scheme of Solana and Sui blockchains was seamlessly upgraded to PQC due to its support for zero-knowledge proofs, which is considered to be a more quantum-secure architecture than Bitcoin's ECDSA.
• Lightweight encryption landing IoT: On August 14, 2025, NIST released the Ascon lightweight encryption standard, with its certified encryption scheme Ascon-AEAD128 requiring only 2.8 KB of memory, providing a secure foundation for constrained endpoints such as sensors and medical implant devices.
• Fully Homomorphic Encryption (FHE) Practicalization: Supports direct computation on encrypted data in the cloud (e.g., medical record analysis), with FHE accelerating its implementation in blockchain privacy transactions (e.g., FHE Rollups) and AI federated learning by 2025.

##Future Outlook From Caesar's letter shift to today's mathematical maze resistant to quantum attacks, encryption has always been the "invisible armor" of the digital world. With the release of the NIST lightweight standard Ascon in 2025, the penetration of FHE in cloud computing, and the quantum security upgrade of blockchain, encryption is no longer just an "art of concealment", but a cornerstone for building trust in digital civilization. As the shadow of quantum computers looms closer (experts predict the threat window will be between 2030 and 2040), this battle over information sovereignty has only just entered a new round.