Comparing .NET PGP Libraries: BouncyCastle vs AlternativesPretty Good Privacy (PGP) remains a widely used standard for encrypting data and signing messages. In the .NET ecosystem there are multiple libraries that implement OpenPGP or provide PGP-like functionality. This article compares the most common options — with a focus on BouncyCastle (the de facto open-source choice) and notable alternatives — to help you pick the right library for your project.
Executive summary
- BouncyCastle is the most mature, full-featured open-source implementation for .NET with broad algorithm support and active usage in production.
- PGPainless / OpenPGP.NET wrappers and other managed libraries aim to simplify usage or provide higher-level APIs, but vary in completeness and maintenance.
- Commercial libraries (e.g., Ilisha/SEAL-style offerings or vendor SDKs) can provide support, polished APIs, and legal assurances but cost money.
- Choose based on requirements: standards compliance and control → BouncyCastle; simplicity and developer ergonomics → higher-level wrappers; enterprise needs and support → commercial offerings.
What features matter when choosing a .NET PGP library
Before comparing libraries, identify the decision criteria that matter for your project:
- Standards compliance: full OpenPGP (RFC 4880) support for keys, packets, signatures, subkeys, etc.
- Cryptographic algorithm coverage: RSA, DSA, ECDSA, EdDSA (Ed25519), ElGamal, AES, SHA variants, AEAD, etc.
- Key management features: creation, import/export (ASCII-armored), keyrings, trust models, revocation, subkeys.
- API ergonomics: ease of use in typical workflows (encrypt/decrypt, sign/verify), async support, integration with streams.
- Performance: throughput for large files, memory usage, streaming support.
- Platform support: .NET Framework, .NET Core / .NET 5+, Xamarin, Mono.
- Security posture: maintenance frequency, vulnerability history, code quality, side-channel mitigations.
- Licensing and legal: OSS license compatibility, patent encumbrances, or commercial licensing.
- Support & ecosystem: documentation, community, examples, and commercial support options.
BouncyCastle (Portable.BouncyCastle / BouncyCastle.Crypto)
BouncyCastle is the most widely used cryptography library in the Java and .NET worlds. For .NET there are two common distributions — the original C# port (BouncyCastle.Crypto) and a Portable/modernized build (Portable.BouncyCastle / Org.BouncyCastle packages on NuGet).
Key strengths
- Comprehensive algorithm support: RSA, ElGamal, DSA, ECDSA, Ed25519 (in newer builds), AES, ChaCha20-Poly1305, HKDF, HKDF-like constructions, and more.
- Mature OpenPGP implementation: supports most OpenPGP features, keyrings, armoring, signatures, and packet-level control.
- Streaming APIs for encrypting/decrypting large files.
- Cross-platform: supports .NET Framework, .NET Core, .NET 5+.
- Free, permissive-ish (MIT-like/BSD-style historically; check specific package license on NuGet).
Limitations
- API is low-level and can be verbose; common tasks require a fair amount of boilerplate.
- Documentation and examples are scattered; learning curve can be steep.
- Historically slower to adopt newer OpenPGP features (AEAD, Ed25519) in some builds — verify current package version for feature parity.
- Some older versions had performance or security issues; choose maintained packages and keep up-to-date.
When to choose BouncyCastle
- You need full control over OpenPGP packets and algorithm selection.
- You require broad algorithm support and cross-platform compatibility.
- You prefer an open-source, no-cost solution and can tolerate some boilerplate.
Example usage (conceptual)
using Org.BouncyCastle.Bcpg.OpenPgp; using Org.BouncyCastle.Security; // create keypair, armor export, encrypt/decrypt via PgpEncryptedDataGenerator, etc. OpenPGP.NET / PGPCore / PgpCore
Several projects wrap BouncyCastle or re-implement parts of OpenPGP to offer simpler APIs. Notable ones include OpenPGP.NET (older), PgpCore, and PGPCore (community projects on NuGet/GitHub). These are not single standardized projects; evaluate each individually.
Key strengths
- Higher-level, developer-friendly APIs that reduce boilerplate for common tasks (encrypt file, decrypt, sign, verify).
- Often provide examples and helpers for integration with ASP.NET, file streams, and modern .NET idioms.
- Many are thin wrappers over BouncyCastle, so they inherit algorithm coverage and some limitations.
Limitations
- Feature completeness varies; some wrappers support only common use cases and omit advanced OpenPGP features (e.g., complex keyrings, certain packet types).
- Maintenance quality varies — some projects are hobby-maintained and may lag on security or compatibility updates.
- Because they delegate crypto to BouncyCastle, they inherit any underlying BouncyCastle issues.
When to choose wrappers
- You want fast implementation of common PGP tasks with minimal boilerplate.
- Your use case is straightforward (file encryption, signing) and doesn’t need deep OpenPGP control.
Example libraries to check
- PgpCore (popular wrapper with examples)
- OpenPGP.NET (older, check maintenance status)
- Various GitHub projects offering convenience helpers
Mozilla’s OpenPGP.js (via interop) and other cross-platform approaches
For applications that span browser and .NET backend (or where you want to share code), you may consider using OpenPGP.js in front-end and a matching library on server. This is not a direct .NET library but affects interoperability decisions (key formats, algorithm support like Ed25519, AEAD).
Considerations
- Ensure both sides support the same cipher suites and key formats.
- Web-based libraries may use different defaults (e.g., curve choices) — explicit configuration helps.
Commercial & enterprise libraries
There are commercial offerings and SDKs that provide OpenPGP or PGP-like capabilities for .NET with enterprise support, hardened implementations, and legal assurances. These include vendor SDKs and security suites from companies that package cryptographic functionality with support contracts.
Key strengths
- Professional support, SLAs, and sometimes formal validation.
- Polished APIs, better documentation, and integration with enterprise systems (HSMs, key provisioning).
- May provide easier compliance with regulatory/legal requirements.
Limitations
- Licensing costs can be significant.
- Vendor lock-in considerations; proprietary APIs may limit migration.
When to choose commercial
- When you need guaranteed support, audits, or enterprise features (HSM/PKCS#11 integration) and are willing to pay.
Comparison table
| Criterion | BouncyCastle (OSS) | High-level wrappers (PgpCore, OpenPGP.NET) | Commercial SDKs |
|---|---|---|---|
| RFC 4880 compliance | High | Medium–High (depends) | High |
| Algorithm coverage | Very broad | Broad (inherits BC) | Broad, may include proprietary optimizations |
| Ease of use | Low (verbose) | High (convenience APIs) | High (polished APIs) |
| Performance | Good (depends on implementation) | Similar to BC | Often optimized |
| Maintenance & support | Community | Varies | Professional support |
| Cost | Free | Free | Paid |
| Platform support | .NET Framework/.NET Core/.NET 5+ | Same as BC | Depends on vendor |
Security considerations and best practices
- Always use maintained and up-to-date package versions; monitor CVEs.
- Prefer libraries that support modern primitives: Ed25519 for signatures, X25519 for encryption, AEAD ciphers like AES-GCM or ChaCha20-Poly1305 where applicable.
- Use stream-based encryption for large files to reduce memory usage.
- Validate implementation defaults — some libraries choose legacy algorithms for compatibility; explicitly configure modern algorithms.
- For key storage, prefer OS/HSM-backed secure storage or encrypted local storage with strict access controls.
- Consider forward secrecy and subkey models for long-running deployments.
- If regulatory compliance matters, choose vendors or libraries that provide necessary attestations or audit trails.
Practical recommendations
- For maximum control, compatibility, and no fees: use BouncyCastle (ensure you pick a maintained NuGet package like Org.BouncyCastle and keep it updated).
- For rapid development and simple use cases: pick a well-maintained wrapper (PgpCore) that delegates to BouncyCastle.
- For enterprise deployments needing support, HSM integration, or compliance guarantees: evaluate commercial SDKs and check their PKCS#11 / HSM support.
- Test interoperability: encrypt with one library and decrypt with another (e.g., BouncyCastle ↔ OpenPGP.js) to confirm compatibility with your intended partners or clients.
Example: minimal workflow checklist for implementing PGP in a .NET app
- Choose a library (BouncyCastle or wrapper).
- Generate keys (use subkeys for encryption and master key for certification).
- Store keys securely (HSM or OS-protected store).
- Implement encrypt/decrypt and sign/verify workflows with streaming.
- Implement key revocation and rotation policies.
- Test interoperability with other OpenPGP implementations.
- Automate dependency updates and monitor security advisories.
Conclusion
BouncyCastle remains the go-to open-source PGP implementation for .NET when you need standards compliance and wide algorithm support; its main drawback is a low-level, verbose API. Higher-level wrappers (PgpCore and others) speed up development for common tasks but vary in completeness and maintenance. Commercial SDKs offer polished APIs and support at a cost. Match your choice to your priorities: control and compatibility → BouncyCastle; developer ergonomics → wrappers; enterprise requirements → commercial vendors.
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