Enabling FIPS-Compliant Cryptography in .NET Applications

.NET has become one of the most widely deployed application platforms in the enterprise, prized for its performance, its cross-platform reach, and a mature ecosystem that runs everything from public web APIs to background services and container workloads.

On Linux in particular, .NET now carries a large share of production traffic. But for organizations operating in regulated environments, performance and portability aren't enough; the underlying cryptography must be validated.

That is where .NET FIPS compliance stops being automatic. The challenge? On Linux, .NET does not ship its own validated cryptographic module. It relies on whatever the operating system provides, and most systems do not provide a FIPS 140-3 validated one.

The Role of .NET in Modern Infrastructure

.NET is a general-purpose runtime and framework, which means it rarely operates on its own. It is usually the layer that ties together services, data, and users.

In regulated deployments, you tend to find it doing work like:

• Serving HTTPS APIs and web applications with ASP.NET Core, terminating or initiating TLS
• Issuing, validating, and signing authentication tokens such as JWTs
• Protecting data at rest through the Data Protection APIs and application-level encryption
• Hashing and verifying credentials and other secrets
• Communicating with databases, message brokers, and downstream services over encrypted channels
• Running inside containers on Debian, Ubuntu, and RHEL-family hosts across multiple CPU architectures

Each of these touches cryptography. And each one inherits whatever cryptographic implementation the platform hands it.

Where Cryptography Actually Happens

Here is the part that surprises many teams. On Windows, .NET routes cryptographic operations through the operating system's CNG libraries. On Linux, it routes them through OpenSSL.

This is documented behavior: the .NET libraries in System.Security.Cryptography delegate the real work to the platform's native crypto stack rather than implementing the primitives themselves.

On Linux, that means OpenSSL performs the operations your application depends on:

• TLS handshakes and record encryption for inbound and outbound connections
• Symmetric encryption and decryption, for example AES
• Hashing and message authentication, for example SHA-2 and HMAC
• Digital signatures and key exchange for RSA and elliptic-curve operations
• Random number generation, which draws from OpenSSL's CSPRNG

So when you ask whether your .NET application is using validated cryptography on Linux, you are really asking a question about OpenSSL. The runtime is a consumer of that module, not the module itself.

The FIPS Compliance Gap

If .NET on Linux uses OpenSSL, and OpenSSL has a FIPS story, why isn't the problem already solved? Because several things have to line up, and by default they don't:

• There is no built-in FIPS switch in .NET on Linux. The runtime does not enforce an approved-algorithm policy for you. It simply calls the OpenSSL it finds.
• The default OpenSSL on a host is usually not a validated module. A stock distribution build of OpenSSL is not the same as a FIPS 140-3-validated cryptographic module operating in its approved mode. Same algorithms, different compliance status.
• Dependency sprawl routes around the platform. .NET projects pull in NuGet packages freely, and some of them, such as managed crypto libraries, implement their own primitives entirely in .NET. Those never touch OpenSSL, so they sit outside any validated boundary no matter what the host is configured to do.
• "FIPS-compliant" host claims can be misleading. A system labeled compliant may not actually be running a validated module in its approved mode, which means the application riding on top inherits a gap it cannot see.

Put simply, is .NET FIPS validated on its own? No. Validation is a property of the cryptographic module, and .NET does not supply one on Linux. You have to bring it.

Why This Matters

Think about what a typical .NET service is trusted with:

• Authenticating users and machines, and minting the tokens that represent those identities
• Encrypting personally identifiable information, health records, financial data, and other regulated content
• Securing communications between services that handle that data
• Signing artifacts and messages whose integrity other systems rely on

If the cryptography behind those functions is not validated, the entire deployment can fail an audit even when the code is correct, and the algorithms look right on paper.

For teams selling into government, defense, healthcare, and finance, FIPS 140-3 is frequently a gate rather than a preference, and a single non-validated crypto path is enough to hold up certification.

A Practical Path Forward: CryptoComply Core

The way to close the gap is to ensure that the OpenSSL .NET links against on Linux is a validated module operating in its approved mode.

That is what CryptoComply Core provides. It is SafeLogic's FIPS 140-3 validated cryptographic module, built as a drop-in for OpenSSL 3.x, which means it presents the same interface .NET already expects:

• FIPS 140-3 validated cryptography under an active CMVP certificate
• Drop-in compatibility with the OpenSSL 3.x API and ABI that .NET consumes on Linux
• Coverage across common server and container platforms, including Debian and RHEL-family distributions, and multiple CPU architectures
• Support for the FIPS-approved algorithms your application relies on, including AES, SHA-2, RSA, and elliptic-curve operations, with a validated random number generator
• A path toward post-quantum readiness as those standards mature

The outcome is that your .NET application keeps using the same System.Security.Cryptography calls it as always has, while the operations underneath run through a validated module rather than an unvalidated one.

Simplifying Compliance Without Rewriting Your Application

The appeal of standardizing on CryptoComply Core is that it moves the compliance boundary to a single, well-defined layer rather than scattering it across your codebase:

• Your application code and its cryptographic API calls stay the same, so there is no rewrite and no new crypto library to learn.
• The validated module becomes one auditable component you can point to, instead of a diffuse set of assumptions about the host.
• The same approach works consistently across the Linux platforms and architectures you deploy on, so behavior doesn't drift between environments.
• You get a documented, certificate-backed answer to the auditor's first question: "Which validated module is doing your cryptography?"

What About Third-Party Crypto Libraries?

Standardizing the platform's OpenSSL only covers the cryptography that flows through OpenSSL.

In .NET, a developer can still add a NuGet package that implements cryptography in managed code and bypasses the validated module entirely, often without realizing the compliance implication.

Closing that door is a governance exercise as much as a technical one:

• Inventory your dependencies and identify any packages that perform their own cryptography rather than delegating to the platform.
• Set a policy that regulated cryptographic operations must route through the validated module, and treat managed-crypto packages as exceptions requiring review.
• Add dependency scanning to CI so that a new package introducing its own primitives is flagged before it reaches production.
• Verify at deployment that the application is actually loading the validated module and running in its approved mode, rather than assuming it.

A Practical Bridge to Compliance

The tension is straightforward. .NET gives you speed, portability, and a huge ecosystem, and that ecosystem is exactly what makes the cryptographic surface hard to pin down.

You don't want to give up the platform's strengths to satisfy a validation requirement, and you don't have to.

The recommended path is:

• Link your .NET Linux workloads to a FIPS 140-3-validated OpenSSL module rather than the stock build.
• Standardize on CryptoComply Core as that module across your environments.
• Govern your dependencies so nothing quietly bypasses the validated path.
• Verify approved-mode operation as part of your release process.

Final Thoughts

.NET earns its place in regulated infrastructure by letting teams build capable, portable services quickly.

Keeping that value while meeting FIPS 140-3 comes down to a few things: understanding that .NET delegates cryptography to OpenSSL on Linux, replacing the default OpenSSL with a validated module, governing the dependencies that could route around it, and verifying approved-mode operation before you ship.

CryptoComply Core supplies the validated foundation that makes those requirements achievable, giving your .NET applications consistent, certificate-backed cryptography without sacrificing the performance and portability that made you choose .NET in the first place.

Further Reading

• Microsoft's cross-platform cryptography guide for .NET
• The NIST Cryptographic Module Validation Program
• The OpenSSL project
• The CryptoComply Core product page
• SafeLogic's overview of CryptoComply's FIPS 140-3 validation