Symmetric encryption is the workhorse of cryptography—the technology that actually protects the vast majority of encrypted data in the world today. When you encrypt a hard drive, secure a database, or protect files in cloud storage, symmetric encryption is almost certainly doing the work.

Its dominance stems from a simple architectural advantage: one key does everything, and it does it extraordinarily fast.

How Symmetric Encryption Works

Symmetric encryption uses a single shared secret key for both transforming plaintext into ciphertext (encryption) and recovering the original plaintext (decryption). The term "symmetric" refers to this mirror-image relationship—both operations use the identical key.

Modern symmetric algorithms achieve security through two cryptographic properties: confusion and diffusion. Confusion makes the relationship between the key and ciphertext as complex as possible—even a single bit change in the key produces completely different ciphertext. Diffusion spreads the influence of each plaintext bit across many ciphertext bits, ensuring that changing one letter in a message changes approximately half of all ciphertext bits.

These properties are achieved through multiple rounds of substitution operations, permutation operations, and mixing with key material. Each individual operation is computationally simple, but the combination creates security through cumulative complexity.

AES: The Global Standard

The Advanced Encryption Standard (AES) is the de facto global standard for symmetric encryption. Adopted by NIST in 2001 after a rigorous five-year competition, AES replaced the ageing Data Encryption Standard and has withstood over two decades of intensive cryptanalysis.

AES operates on fixed 128-bit blocks and supports key lengths of 128, 192, or 256 bits. The "128", "192", and "256" designations refer to key length, not block size—AES-256 does not encrypt larger blocks, it uses a longer key providing greater security against brute-force attacks.

Modern processors include dedicated AES instructions (Intel's AES-NI, ARM's Cryptography Extensions) that dramatically accelerate operations. These hardware implementations encrypt data at multiple gigabytes per second with minimal CPU overhead, making AES not only secure but extraordinarily fast.

ChaCha20: The Software Alternative

ChaCha20 is a modern stream cipher designed for high performance in software implementations. Unlike AES, which was designed when hardware acceleration was not universally available, ChaCha20 was explicitly created to maximise speed in pure software, particularly on mobile devices and embedded systems lacking dedicated cryptographic hardware.

ChaCha20's design relies on simple arithmetic operations that modern CPUs execute efficiently. It avoids the complex lookup tables used by AES, making it naturally resistant to certain timing-based attacks that can compromise AES software implementations.

Google selected ChaCha20 for TLS connections to mobile devices, and it underlies the WireGuard VPN protocol. In environments without hardware AES acceleration, ChaCha20 often outperforms AES significantly.

Authenticated Encryption

Traditional encryption modes guarantee only confidentiality—they hide data content but provide no protection against tampering. An attacker who intercepts encrypted data can flip specific bits in the ciphertext, causing predictable changes in the decrypted plaintext. This enables dangerous bit-flipping attacks even without knowing the key.

Authenticated Encryption with Associated Data (AEAD) schemes solve this problem by combining encryption and authentication into a single algorithm. AEAD produces both ciphertext and an authentication tag in one operation. Any tampering with the ciphertext causes authentication to fail, preventing the attack.

AES-GCM (Galois/Counter Mode) is the preferred AEAD mode, providing both encryption and authentication with excellent performance. ChaCha20-Poly1305 offers equivalent protection for environments better suited to ChaCha20. Modern security protocols mandate AEAD modes—non-authenticated modes should be avoided.

The Key Distribution Challenge

Symmetric encryption's central challenge is key distribution. Both communicating parties must possess the identical secret key before they can communicate securely. If an attacker intercepts the key during exchange, all subsequent encrypted communication is compromised.

This challenge is why symmetric encryption works alongside asymmetric encryption in hybrid cryptosystems. Asymmetric encryption solves the key distribution problem, establishing a shared symmetric key securely. Symmetric encryption then provides the speed needed for bulk data protection. For more on how these cryptographic systems work together, see our guide to What is PKI.

When to Use Symmetric Encryption

Symmetric encryption is the right choice for bulk data protection—encrypting databases, file systems, backups, and network traffic. Its speed makes it the only practical option for high-volume encryption.

Use AES-GCM when hardware acceleration is available or when regulatory compliance requires NIST-approved algorithms. Use ChaCha20-Poly1305 for software-only implementations, mobile devices, or embedded systems. In both cases, ensure you are using authenticated encryption modes—never use unauthenticated modes for new implementations.

How Unsung Helps

While symmetric encryption is often straightforward to implement, integrating it properly into enterprise infrastructure—with appropriate key management, secure key distribution, and operational practices—requires expertise. Unsung helps organisations design cryptographic architectures that protect data effectively.

Our PKI expertise ensures the asymmetric infrastructure that distributes symmetric keys is properly designed and managed. We help implement key management solutions using Hardware Security Modules that scale and maintain security throughout the key lifecycle.

Contact Unsung to discuss how we can help with your data protection strategy.