Symmetric Key Encryption for Medical Devices: A Practical Guide to AES and Key Management

Symmetric key encryption shows up everywhere in modern connected products—including medical devices. If your device talks to a cloud service, exchanges data with a mobile app, stores logs locally, or supports remote service, symmetric encryption is almost certainly part of the picture.

This guide explains symmetric key encryption in plain English, then connects it to the realities of medical device cybersecurity: performance constraints, clinical impact, key management at scale, and the kind of evidence you’ll want available for premarket and postmarket needs.

Understanding Symmetric Key Encryption

Definition and basic principles

Symmetric key encryption uses the same key to encrypt and decrypt data. Think of it like a single key that locks and unlocks a door. If you have the key, you can read the data. If you don’t, the encrypted data should be useless to you.

In practice, a symmetric algorithm takes your original message (plaintext) and transforms it into an unreadable format (ciphertext). The same key is then used to reverse the process.

Where symmetric encryption shows up in medical devices

Medical device teams commonly run into symmetric encryption in a few places:

Device-to-cloud communication (for example, secure telemetry sessions)
Device-to-mobile app communication (pairing, sessions, and protected payloads)
Data at rest on the device (logs, PHI caches, configuration, crash dumps)
Backend storage (databases and object storage encrypted at rest)
Manufacturing and service workflows (provisioning keys, protected service channels)

Why it matters in MedTech

Encryption is often described as “confidentiality,” but in medical devices it’s usually bigger than that. You may also need integrity protection (prevent tampering) and operational safety considerations (availability and clinical workflow). Symmetric encryption can support all of this—but only when paired with sound key management and well-chosen implementations.

Types of Symmetric Key Encryption

Data Encryption Standard (DES)

DES is an older algorithm from the 1970s. It’s an important part of cryptography history, but it’s not what modern medical device teams should be building around today. If you see DES in a product, it’s usually a legacy compatibility requirement—and it’s worth revisiting.

Advanced Encryption Standard (AES)

AES is the modern workhorse. It supports 128-, 192-, and 256-bit keys and is widely adopted across industry. If you need a default “safe choice” for symmetric encryption, AES is usually it. (NIST defines AES in FIPS 197.)

Reference:
NIST FIPS 197 (AES)

Blowfish and Twofish

Blowfish and Twofish are well-known symmetric algorithms. You’ll still see them in some libraries or older designs, but most medical device teams standardize on AES today for interoperability and ease of justification.

How Symmetric Key Encryption Works

Key generation and distribution

Symmetric encryption is only as strong as its key management. In real products, “key distribution” is the hard part: both sides need the same secret, and that secret has to be created, stored, rotated, and protected over time.

In many medical device architectures, symmetric keys are used as session keys. A secure protocol (often using asymmetric cryptography during handshake) establishes a session, then symmetric encryption protects the data flow because it’s fast and efficient.

If you ever have to derive a key from a password or passphrase (for example, a human-entered credential), use a proper password-based key derivation function rather than “rolling your own.” NIST SP 800-132 covers password-based key derivation techniques.

References:
NIST SP 800-132,
NIST SP 800-57 (Key Management)

Encryption and decryption (what’s actually happening)

At a high level, the encryption algorithm transforms plaintext into ciphertext using mathematical operations and the key. Decryption uses the same key to reverse the process.

One point that matters for device teams: “AES” is not one single thing. The mode of operation matters. For many applications, an authenticated encryption approach is preferred because it helps protect both confidentiality and integrity. NIST SP 800-38D specifies AES-GCM, a widely used authenticated encryption mode.

Reference:
NIST SP 800-38D (GCM)

Strengths and Weaknesses of Symmetric Key Encryption

Advantages

Efficiency: Symmetric encryption is fast, which matters for real-time telemetry, battery-powered devices, and low-latency workflows.
Scalability: It can handle large volumes of data without becoming a bottleneck.
Practicality: It’s widely supported and relatively straightforward to implement correctly when paired with good libraries and key management.

Potential drawbacks and risks (what bites medical device teams)

Key distribution: Sharing secrets safely is hard—especially across manufacturing, service, and field deployments.
Fleet-wide blast radius: Reusing the same key across devices is risky. A single leak can become a “one key unlocks everything” event.
Key storage: If keys are exposed in firmware, logs, backups, or poorly protected storage, encryption won’t save you.
Lifecycle challenges: You need a plan for rotation, revocation, recovery, and incident response—not just a plan to encrypt once.

In practice, the most common failure isn’t “we picked AES-128 instead of AES-256.” It’s weak key management: hardcoded secrets, shared keys, poor provisioning, or no clear rotation strategy.

Applications of Symmetric Key Encryption in Medical Device Ecosystems

Secure communication

Symmetric encryption is commonly used to protect data in transit once a secure session is established. This is one reason it’s so important for remote monitoring, device-to-cloud telemetry, and clinician-facing dashboards.

Data protection and privacy (data at rest)

Devices and backend systems often store sensitive information: PHI, troubleshooting logs, configuration snapshots, audit trails, and crash dumps. Encrypting data at rest helps reduce the risk if a device is lost, stolen, accessed by an unauthorized person, or serviced outside controlled environments.

Key management and operational reality

If you want symmetric encryption to actually reduce risk, it needs to connect to operational processes: how devices are provisioned, how service tools authenticate, how keys are protected during manufacturing, and how vulnerabilities are handled after release.

Related reading: Exploring Key Management Protocols

What FDA reviewers care about when you mention encryption

When encryption shows up in your cybersecurity story, the questions that matter are usually practical:

What are you encrypting? (PHI, telemetry, configuration, logs, update payloads, credentials)
Where is encryption applied? (on-device storage, transport sessions, backend storage)
How are keys generated, stored, rotated, and revoked?
How do you prevent single points of failure? (per-device keys, separation of duties, limiting access)
What verification evidence exists? (test results, configuration reviews, threat model outputs)

If your device is connected (or becomes connected through accessories, apps, or cloud services), encryption is rarely “just a feature.” It’s part of an overall secure design story that includes threat modeling, testing, SBOM management, and postmarket response.

If you want help turning “we use AES” into a defensible, submission-ready and lifecycle-ready story, these resources are a good place to start:

Future of Symmetric Key Encryption

Quantum computing and symmetric encryption

Quantum computing is often discussed as a major cryptography disruptor. Practically, many teams handle this by planning for crypto agility (the ability to update cryptography over time) and choosing modern, well-supported algorithms and key sizes now so they aren’t stuck later.

Trends that matter for connected devices

As medical devices continue to adopt cloud connectivity and software-based features, the “encryption conversation” shifts from algorithms to operations: key provisioning, secure updates, monitoring, and how quickly you can respond when a dependency vulnerability lands.

FAQs

Do medical devices need AES-256?

Not always. AES-128 is strong for many use cases. The bigger question is usually key management: how keys are generated, stored, protected, rotated, and revoked. If you want a conservative approach for long-lived data or higher-risk environments, AES-256 can be a reasonable default—assuming performance supports it.

What matters more: AES key size or key management?

In most real incidents, key management is the weakness. Hardcoded keys, shared secrets across a fleet, poor provisioning, or lack of rotation/revocation planning can undermine otherwise strong encryption.

Where should encryption keys be stored on a medical device?

Prefer hardware-backed protection where feasible (for example, secure elements or trusted platform features). At a minimum, keys should be protected from extraction and not embedded directly in firmware in a way that can be trivially recovered.

How do we rotate keys in deployed devices?

Key rotation is easiest when it’s designed in early: per-device identity, secure update mechanisms, and a documented lifecycle plan. If your device is already deployed, rotation may still be possible, but it should be approached as a risk-managed change with clear testing and rollback strategies.

Is encryption enough to meet FDA cybersecurity expectations?

Encryption is important, but it’s only one control. You also need secure design practices, verification testing, dependency visibility (e.g., SBOM), and a postmarket plan for monitoring and responding to vulnerabilities.

Conclusion: maximizing security with symmetric encryption

Symmetric key encryption is a core building block for protecting medical device data and communications—especially because it’s efficient enough to use in real products. But the “win” doesn’t come from naming an algorithm. It comes from implementing encryption in a way that holds up under real-world conditions: good key management, solid verification, and a lifecycle plan.

If you want a second set of eyes on your encryption approach—or you need to turn it into submission-ready evidence—Blue Goat Cyber can help you assess, document, and validate security controls in a way that supports both premarket and postmarket success.

Contact Blue Goat Cyber or schedule a discovery session.