What Is Data Encryption

Data encryption is the technology of converting plaintext (readable data) into ciphertext (unreadable data) using a cryptographic algorithm and a key. Since only those with the correct key can decrypt the data back to its original plaintext, it is the most fundamental means of protecting data confidentiality.

Encryption is used in two main scenarios. One is "Encryption at Rest," which encrypts data stored on storage. It defends against disk theft and unauthorized access to storage. The other is "Encryption in Transit," which encrypts data flowing over a network. TLS/SSL is the prime example.

In modern security design, combining both is a standard requirement.

How Symmetric and Asymmetric Encryption Work

Encryption methods are broadly classified into symmetric-key encryption and public-key (asymmetric) encryption.

Symmetric-key encryption uses the same key for both encryption and decryption. The representative algorithm is AES (Advanced Encryption Standard), which offers key lengths of 128, 192, and 256 bits. It is fast and suitable for encrypting large volumes of data. The challenge is key sharing - a secure means of delivering the key to the communication partner is required.

Public-key encryption uses two different keys: a public key for encryption and a private key for decryption. RSA and Elliptic Curve Cryptography (ECC) are representative examples. Since the public key can be distributed to anyone and only the holder of the private key can decrypt, it solves the key distribution problem. However, it is slower than symmetric-key encryption and is not suited for encrypting large data volumes.

In actual communications, a hybrid approach is standard: public-key encryption is used to securely exchange a symmetric key, which then encrypts the data payload. TLS/SSL operates exactly this way.

Encryption Implementation Patterns and Selection Criteria

Here are the main patterns for deploying encryption in practice.

Disk Encryption: Encrypts the entire storage at the OS level. Representative examples include BitLocker on Windows, FileVault on macOS, and LUKS on Linux. Effective as device encryption against device loss or theft.

File-Level Encryption: Encrypts only specific files or folders. This pattern includes cloud storage with end-to-end encryption support and file encryption using PGP/GPG.

Database Encryption: There are two approaches - TDE (Transparent Data Encryption), which encrypts the entire database file, and column-level encryption, which encrypts only specific fields. Column encryption requires application-side implementation but provides strong protection that prevents even DBAs from seeing plaintext.

As selection criteria, comprehensively evaluate the scope of protection, performance impact, operational overhead of key management, and compliance requirements (such as cloud storage security standards).

The Importance and Practice of Key Management

The security of encryption depends not only on algorithm strength but also on proper key management. No matter how strong the encryption algorithm, if the key is leaked, the data can be decrypted.

The fundamental principles of key management are: (1) do not store keys and encrypted data in the same location, (2) implement key rotation (periodic renewal), (3) control access to keys based on the principle of least privilege, and (4) establish key backup and recovery procedures.

In cloud environments, it is practical to use managed key management services such as AWS KMS, Azure Key Vault, or Google Cloud KMS. These services protect keys with HSMs (Hardware Security Modules) and provide integrated key rotation, access control, and audit logging.

Since losing a key means permanently losing the ability to decrypt data, key backup is one of the most critical elements of an encryption strategy.

To learn more about this topic, see Device Encryption Basics: Protecting Data on Your PC and Smartphone.

Common Misconceptions

Since communication uses HTTPS, data on the server is also encrypted: HTTPS (TLS) encrypts the communication path, but data is decrypted and processed/stored in plaintext once it reaches the server. To protect data on the server, encryption at rest must be implemented separately.
Encrypting data eliminates the risk of data breaches entirely: Encryption protects data confidentiality, but risks remain from key leakage, implementation vulnerabilities, and side-channel attacks. Additionally, encryption does not directly contribute to tamper detection or availability protection. Position it as one element of defense in depth.

Comparison of Symmetric and Asymmetric Encryption

Symmetric-Key Encryption (AES, etc.)

Uses the same key for encryption and decryption. Fast processing speed, suitable for large data volumes. Secure key sharing is the challenge. 128/256-bit key lengths are mainstream.

Public-Key Encryption (RSA/ECC, etc.)

Uses a public key and private key pair. Solves the key distribution problem but processing is slow. Also used for digital signatures. RSA 2048-bit or higher, or ECC 256-bit or higher is recommended.

Data Encryption