Choosing the Best .NET PGP Library in 2025: Features, Performance, and Security

Top .NET PGP Libraries Compared: OpenPGP Implementations for C# DevelopersSecure encryption and signing are foundational for many applications — from secure email and file storage to code signing and secure messaging. For C# and .NET developers wanting OpenPGP-compatible tools, several libraries provide implementations of the OpenPGP standard (RFC 4880) with varying focuses: ease of use, performance, cross-platform compatibility, licensing, and feature completeness. This article compares the leading .NET PGP libraries, shows practical usage patterns, and gives guidance on picking the right library for your project.

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Why OpenPGP in .NET?

OpenPGP is widely used for encrypting messages and files and for signing data so recipients can verify authenticity. In .NET ecosystems you may need OpenPGP when:

• Building secure email clients or services (PGP/MIME).
• Encrypting files or blobs for long-term confidentiality.
• Signing data or packages for integrity and non-repudiation.
• Interoperating with existing PGP tooling and workflows.

Key selection criteria:

• RFC 4880 compliance and interoperability with GnuPG/other clients.
• Active maintenance and security responsiveness.
• Cross-platform support (Windows, Linux, macOS) especially for .NET Core / .NET 6+.
• API ergonomics and documentation.
• Performance and memory characteristics.
• Licensing that fits your project (MIT, Apache, commercial).

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Libraries compared

Below are the most notable .NET PGP/OpenPGP libraries available to C# developers as of 2025.

• BouncyCastle (Portable.BouncyCastle / Org.BouncyCastle)
• PgpCore
• GPGME/Wrappers (using external gpg binary)
• MimeKit.Cryptography (PGP via BouncyCastle integration)
• Pgpainless.NET (bindings/wrappers around strong Java implementations — niche)
• OpenPGP.Core (smaller/open-source implementations)

We’ll compare their compatibility, API style, strengths and typical use-cases.

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BouncyCastle (Org.BouncyCastle / Portable.BouncyCastle)

Overview

• A long-standing cryptography library that includes OpenPGP support.
• Low-level, feature-rich, implemented in C# (Org.BouncyCastle).
• Widely used as a cryptographic foundation in many projects.

Pros

• Full feature set for OpenPGP: key generation, encryption/decryption, signatures, compression, armored output, packet-level operations.
• Pure managed implementation — no external native dependencies.
• Cross-platform with .NET Standard/.NET 6+ builds.
• Mature, well-tested codebase.

Cons

• Low-level API; steeper learning curve for common tasks.
• Historically, some API surface can be cumbersome and verbose.
• Performance may be lower than optimized native implementations for certain workloads.

Typical uses

• Projects that need a pure .NET implementation without external dependencies.
• When fine-grained control over OpenPGP packets is required.

Example (encrypting a stream)

using Org.BouncyCastle.Bcpg.OpenPgp; // (High-level pseudocode) using var publicKeyStream = File.OpenRead("pub.asc"); using var output = File.Create("message.pgp"); PgpPublicKey pubKey = ReadPublicKey(publicKeyStream); EncryptFile(output, "plaintext.txt", pubKey); 

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PgpCore

Overview

• A higher-level wrapper built on top of BouncyCastle that simplifies common PGP tasks.
• Focuses on convenience: simple methods to encrypt, decrypt, sign, verify, and generate keys.

Pros

• Much easier to use than raw BouncyCastle for typical scenarios.
• Reduces boilerplate for file/stream-based operations.
• Good for quick integration in applications.

Cons

• Less flexible for low-level packet manipulation.
• Depends on BouncyCastle for crypto; any BouncyCastle issues propagate.

Typical uses

• Web apps, desktop apps, or services needing straightforward PGP functionality with minimal code.

Example

using PgpCore; using (PGP pgp = new PGP()) {     pgp.EncryptFile("input.txt", "encrypted.pgp", "publicKey.asc", true, true); } 

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GnuPG / gpg binary wrappers (GPGME, invoking gpg)

Overview

• Leverages the widely-used GnuPG native implementation by invoking the gpg executable or using GPGME bindings.
• Not a pure .NET library but provides interoperability with the established GnuPG toolchain.

Pros

• Very high interoperability with existing PGP ecosystems (GnuPG features, keyrings, trust models).
• Often faster and battle-tested in the wild.
• Supports smartcards (YubiKey), advanced key management, and native trust models.

Cons

• Requires installation of GnuPG on the host and appropriate configuration.
• Platform/environment dependency — more complexity in deployment (containers, CI).
• Invoking external processes or native bindings can complicate error handling and security (credential isolation).

Typical uses

• When you need the GnuPG trust model, use of hardware tokens, or must match a system’s GnuPG keyring.
• System-level tooling, CLI integrations, or desktop apps where installing gpg is acceptable.

Example (invoking gpg)

gpg --encrypt --recipient [email protected] --output message.gpg message.txt 

In .NET you’d call this via Process.Start or use a GPGME wrapper for managed bindings.

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MimeKit.Cryptography (MimeKit + MailKit)

Overview

• MimeKit is a robust MIME parser with cryptography support through its Cryptography classes; it uses BouncyCastle internally for OpenPGP operations.
• Designed for email scenarios (PGP/MIME), integrating seamlessly with MailKit.

Pros

• Excellent for email signing/encryption workflows.
• High-level primitives designed for message composition and parsing.
• Good documentation and maintained by an active author.

Cons

• Focused primarily on email; not a general-purpose PGP toolkit for arbitrary files (though it can be used for that).
• Relies on BouncyCastle for cryptographic primitives.

Typical uses

• Building email clients/servers that need PGP/MIME support, signing, and verification.

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OpenPGP.Core and smaller implementations

Overview

• Lightweight or experimental implementations that focus on smaller footprints, simpler APIs, or specific subsets of OpenPGP.
• May be suitable for embedded scenarios or where only a subset of functionality is needed.

Pros

• Small and easy to include.
• Sometimes permissive licenses.

Cons

• Limited feature set; may not fully interoperate with all PGP implementations.
• Less mature and less likely to be actively maintained.

Typical uses

• Minimal encryption needs or constrained environments.

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Direct comparison

Library	Pure .NET	Level	Best for	Licensing
BouncyCastle (Org.BouncyCastle)	Yes	Low-level, full feature	Full control, no external deps	MIT/BouncyCastle license variants
PgpCore	Yes (wraps BouncyCastle)	High-level convenience	Quick integration, file ops	MIT
GnuPG (gpg/GPGME)	No (native)	System-level, full-feature	Interop with keyrings, hardware tokens	GPL (GnuPG) / LGPL for GPGME
MimeKit.Cryptography	Yes (uses BouncyCastle)	High-level (email-focused)	PGP/MIME for email apps	MIT
OpenPGP.Core (various)	Varies	Minimal/experimental	Lightweight needs	Varies (check repo)

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Security considerations

• Prefer well-maintained and actively patched libraries (BouncyCastle has a long history of CVE handling).
• Validate key management: private keys must be stored securely (encrypted at rest, access controlled); consider hardware-backed key storage for high-risk apps.
• Use modern algorithms and sufficient key sizes (RSA 2048+ or better: ⁄₄₀₉₆, or ECC where supported).
• Beware of API misuse: encrypt-then-MAC or authenticated encryption patterns reduce certain attacks. OpenPGP has its own constructions—know them.
• Consider threat model: if you must interoperate with GnuPG users, test with GnuPG extensively.

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Practical examples and patterns

1. Typical file encryption flow (general):

• Recipient exports public key (ASCII-armored).
• Sender loads public key and encrypts file to PGP message (binary or ASCII-armored).
• Recipient decrypts with private key, optionally verifying signature.

1. Signing + encryption:

• Sign payload with sender’s private key.
• Encrypt signed payload with recipient’s public key.
• Recipient decrypts and verifies signature chain.

1. Key generation:

• Use library support or GnuPG to generate RSA or ECC keys, set expiry, user IDs, and subkeys for encryption/signing.

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Recommendations

• If you need a pure .NET solution and full control: use BouncyCastle (Org.BouncyCastle). For most developers who want simpler APIs, use PgpCore on top of BouncyCastle.
• For email-focused projects: use MimeKit/MailKit with its cryptography layer.
• If you depend on system keyrings, smartcards, or strict GnuPG interoperability: use the native GnuPG binary or GPGME bindings.
• For constrained or minimal use-cases: evaluate smaller implementations but vet interoperability and security.

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Checklist before production

• Confirm licensing compatibility with your project.
• Run interoperability tests with GnuPG and other PGP clients.
• Ensure secure private key storage (encrypted storage, access controls, HSM/YubiKey if needed).
• Implement logging and monitoring for cryptographic operations and key lifecycle events.
• Keep libraries and dependencies updated; subscribe to CVE notifications for chosen libraries.

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If you want, I can:

• produce example code for one library (BouncyCastle or PgpCore) showing key generation, encrypt/decrypt, and sign/verify;
• or create a short decision flowchart to pick the right library for your project.