What is Encryption? Symmetric, Asymmetric and Quantum-Safe

Every second, billions of sensitive transactions are protected as they flow across the internet — bank transfers, medical records, confidential business communications and personal messages. None of it would be possible without encryption.

For organisations creating, processing or transmitting sensitive data, understanding encryption is no longer optional. Regulatory frameworks mandate it, customers expect it, and security incidents increasingly exploit its absence or misconfiguration.

What is encryption?

Encryption is the process of transforming readable information, called plaintext, into an unintelligible scrambled form called ciphertext, using a mathematical algorithm and a secret key. Only parties holding the correct key can reverse the transformation and recover the original information.

Most of the encryption you rely on is applied without you knowing it is there, handled by applications or inside your browser. A more visible example is cybercrime, where it is weaponised: ransomware scrambles an organisation's data into an unreadable form, allowing criminals to demand payment for the key to unscramble it.

The security of any encryption system rests on a single principle. Without the correct key, breaking the mathematical algorithm must be infeasible with current computing capabilities. That principle has held for more than forty years with the algorithms in use across that period. Cracking AES-256 with all the computing power available today would take longer than the universe has existed.

Quantum computing changes that dynamic, though not in the way most coverage suggests. We cover it below and in detail in our guide to post-quantum cryptography.

Symmetric and asymmetric encryption

There are two fundamental approaches, and almost every real system uses both together.

Symmetric encryption

One shared key performs both operations. The same key that encrypts the data decrypts it.

This is fast — modern processors include dedicated instructions for it, encrypting at multiple gigabytes per second — which makes it the right choice for bulk data: databases, file systems, backups, network traffic.

The dominant algorithm is AES, adopted by NIST in 2001 and now the global standard. ChaCha20 is the main alternative, designed for software performance on devices without cryptographic hardware. Our guide to symmetric encryption and AES covers both.

Its weakness is key distribution. Both parties need the identical secret key before they can communicate, and getting it to them securely is the problem symmetric encryption cannot solve on its own.

Asymmetric encryption

Two mathematically linked keys. A public key, shared openly, and a private key, kept secret and never shared.

Data encrypted with the public key can only be decrypted with the private key, and a signature created with the private key can be verified by anyone holding the public key. That second property is what allows identity to be proven remotely.

The two most widely used algorithms are RSA, which derives its security from the difficulty of factoring large numbers, and elliptic curve cryptography, which relies on the difficulty of the discrete logarithm problem on elliptic curves. ECC achieves equivalent security with much shorter keys, which is why it has displaced RSA in most new deployments.

Asymmetric encryption solves key distribution. Its weakness is speed — it is typically two to three orders of magnitude slower than symmetric encryption, which makes it impractical for bulk data.

Why real systems use both

Comparing raw key lengths between the two is meaningless. RSA-2048 provides roughly 112 bits of security, less than AES-128 despite a far longer key, because asymmetric security depends on mathematical problem complexity rather than key space size.

In practice the two are combined into a hybrid arrangement. When you connect to a website over HTTPS, asymmetric cryptography authenticates the server and negotiates a shared session key. Symmetric encryption then protects the actual data using that key. You get the trust properties of one and the performance of the other.

Public Key Infrastructure is the framework that makes the asymmetric half workable at scale, by issuing and managing the certificates that bind public keys to verified identities.

The three states of data

Multiple encryption methods exist because data exists in three distinct states, each presenting different challenges.

Data at rest is information stored on physical or virtual storage — databases, hard drives, cloud storage, backup systems. It faces unauthorised access, physical theft of storage devices and insider threats. A stolen laptop or compromised server could expose vast quantities of sensitive information if that data is not properly encrypted.

Data in transit is information actively moving between locations, across networks or between devices and services. As it travels it becomes vulnerable to interception, and attackers can eavesdrop at vulnerable points in the network path.

Data in use is information actively being processed by applications, cloud services or business processes. Data typically has to be decrypted and readable before any useful work can be performed, which creates an obvious gap during processing. Confidential computing and homomorphic encryption are the emerging approaches to closing it, though both remain considerably less mature than encryption of data at rest or in transit.

Why encryption alone is not enough

You would be forgiven for thinking that simply encrypting information mitigates all risk. Encryption provides confidentiality — keeping data secret — but it does not inherently provide integrity, meaning assurance that data has not been tampered with, or authenticity, meaning confirmation of the sender's identity.

Consider a scenario. Alice encrypts a message to Bob saying "Please transfer £100 to account A". An attacker intercepts the ciphertext. Even without reading the message, they might modify specific bits in predictable ways. When Bob decrypts the modified ciphertext, it might read "Transfer £1000 to account B". Confidentiality was maintained. Integrity was not.

The answer is authenticated encryption, which combines encryption with message authentication to ensure both properties in a single operation. AES-GCM and ChaCha20-Poly1305 are the standard modes, and modern protocols mandate them. Unauthenticated modes should not be used in new systems.

The human element: where encryption fails

Encryption is only as strong as its weakest link, and that link is usually human behaviour or implementation error rather than any weakness in the algorithms.

The most common failures:

• Weak passwords that can be guessed or cracked, particularly where keys are derived from them without a proper key derivation function.
• Key reuse across multiple systems, so that one compromise cascades.
• Poor key storage — hardcoded in source code, sitting in configuration files, or held on the same system as the data they protect.
• Implementation vulnerabilities, including those that exploit error handling to reveal information about the key.
• Social engineering that tricks users into revealing keys or bypassing encryption altogether.

Even the most sophisticated algorithm provides zero security if the key is written on a Post-it attached to the monitor. Understanding what makes encryption keys secure, how to generate them properly, and why key management is the critical vulnerability in most systems is what turns encryption policy into genuine data protection.

Where keys underpin a trust hierarchy or protect high-value data, hardware security modules provide protection that software keystores cannot — the key material never exists in plaintext outside the device, and cannot be extracted even by administrators.

What quantum computing changes

This is the most misunderstood part of the subject, and the answer is more reassuring than most coverage suggests. The threat is not uniform across encryption. It falls almost entirely on one half of it.

Symmetric encryption is largely unaffected

Grover's algorithm offers a quadratic speedup against symmetric key search, which effectively halves key strength. AES-256 drops to 128 bits of post-quantum security, which remains computationally infeasible to attack.

NIST has not proposed a replacement for AES because none is required. The guidance is straightforward: keep using it, and prefer AES-256 where data has a long confidentiality requirement.

Asymmetric encryption is the problem

Shor's algorithm breaks RSA and elliptic curve cryptography outright, by solving efficiently the mathematical problems those algorithms depend on. Increasing key length does not help — a cryptographically relevant quantum computer breaks RSA-4096 as readily as RSA-2048.

That means the exposure sits in key exchange, digital signatures and identity, not in the bulk encryption protecting your data. Which in turn means quantum readiness is a PKI and key management problem before it is an encryption problem.

Quantum-safe, quantum-resistant, post-quantum

These terms are used interchangeably and mean the same thing: cryptography designed to remain secure against both classical and quantum computers. You will also see quantum-proof, which is the same claim in less careful language.

They should not be confused with quantum key distribution, which uses quantum physics to distribute keys and requires specialised hardware. Post-quantum cryptography runs on ordinary computers and is what standards bodies are actually recommending.

NIST published the first post-quantum standards in 2024 — ML-KEM for key encapsulation and ML-DSA and SLH-DSA for digital signatures, all based on lattice or hash constructions rather than factoring. Our guide to the NIST post-quantum roadmap covers the standards and the timeline.

Why this matters now

Cryptographically relevant quantum computers do not yet exist. The risk is still current, because encrypted data can be captured and stored today and decrypted later once the capability arrives. Any data with a confidentiality requirement extending beyond a decade is already exposed to this harvest now, decrypt later risk.

The practical response is not to replace algorithms immediately. It is to know what you have — which algorithms, which key lengths, protecting what — and to build the ability to change them. That capability is crypto-agility, and a cryptographic bill of materials is where it starts.

Encryption in practice

In daily use, encryption works invisibly but constantly. HTTPS protects your connection to a website from eavesdropping. End-to-end encryption in messaging apps ensures only the recipient can read a message. Cloud storage encryption protects files from unauthorised access.

Understanding what encryption protects, and what it does not, is critical. It provides one specific security control: protecting data from unauthorised access. That mitigates several risks but not all of them.

Encryption does not:

• Protect against malware already running on your device.
• Hide metadata — who you are communicating with, when, and how often.
• Prevent authorised users from misusing data they legitimately accessed.
• Help if the key is compromised, which is why key management matters more than algorithm choice.

Practical implementation should therefore sit within your wider security controls, complementing other capabilities to provide defence in depth.

How Unsung helps with encryption and key management

Effective encryption is not simply a technology challenge. It depends on business considerations: where your data resides, its sensitivity, how it is used in your applications, and the threats specific to your sector.

From a technology perspective it relies on a performant, accessible PKI capability, cryptographic controls embedded into applications, and proper key management.

Our specialists help organisations implement encryption strategies that go beyond selecting algorithms to address the operational realities of key lifecycle management. We assess current cryptographic practices, identify process and technology gaps, and design solutions that balance security with operational requirements.

Whether you need to implement hardware security modules for key protection, establish certificate-based encryption infrastructure through PKI design and build, or prepare for post-quantum cryptography with PKI consultancy, our vendor-neutral expertise guides you to fit-for-purpose solutions.

A PKI health check establishes the current position. Contact us to discuss strengthening your encryption and key management practices.