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A Secure Shell (SSH2) client and server protocol library, implemented in both C# and TypeScript.

• SSH over any .NET Stream or JavaScript stream (including but not limited to TCP socket streams)
• Configurable, extensible, negotiated algorithms for key-exchange, encryption, integrity (HMAC), and public-key authentication
• Channel multiplexing, with ability to stream data to/from channels
• Port-forwarding, with ability to stream data to/from remote ports
• Piping between two sessions can relay all channels and port-forwarding
• Extensible channel request handling (for "exec", "shell", or custom requests)
• Supports reconnecting a disconnected session without disrupting channel streams.
• Compatible with common SSH software. (Tested against OpenSSH.)
• Supports importing and exporting several key formats, including password-protected keys.

The following features are not implemented in this library, though they could be built on top of it:

• Allowing a client to login to a user account on the server
• Connecting to a shell on the server
• Invoking shell commands on the server
• Transferring files (SCP or SFTP)
• Rendering a terminal on the client side

Future development may add support for some of these capabilities, likely in the form of additional optional packages.

The C# library targets .NET Framework 4.8, .NET Standard 2.1 (.NET Core 3.1, .NET 5), and .NET 6. It's tested on Windows, Mac, & Ubuntu. For details about the .NET library, see src/cs/Ssh/README.md.

The TypeScript implementation supports either Node.js (>= 14.x) or a browser environment. The Node.js version is tested on Windows, Mac & Ubuntu; the browser version is tested on Chrome & Edge Chromium, though it should work in any modern browser that supports the web crypto API. Note that since script on a web page cannot access native TCP sockets, the standard use of SSH over TCP is not possible; some other stream transport like a websocket may be used. For details about the TypeScript library, see src/ts/ssh/README.md.

The optional "keys" and "TCP" packages depend on the core package. All SSH packages in an app must be the same major and minor version; the patch version (3rd component) may differ if necessary. In other words, any changes that impact cross-package dependencies will increment at least the minor version.

See README-dev.md.

Crypto algorithms below rely on platform APIs in .NET (System.Security.Cryptography), Node.js (crypto module) or browsers (web crypto). There is one use of a 3rd-party library: the diffie-hellman package is required in browsers because there is no corresponding web crypto API.

Legend:
✔✔✔ - Enabled and preferred in default session configuration.
✔✔ - Enabled (but not preferred) in default session configuration.
✔ - Supported and can be enabled in custom session configuration.
☑ - Coming soon (working in a branch or PR).
?? - Under consideration for the future.

[1] May require use of 3rd-party libs, though Curve25519 APIs are under consideration for .NET and web crypto.
[2] OpenSSH certificate support should be possible with some work.
[3] AES-CBC is not supported in browsers due to a limitation of the web crypto API. AES-CTR or AES-GCM works fine.

There is no plan to have built-in support for older algorithms known to be insecure (for example SHA-1), though in some cases these can be easily added by the application.

Support for importing and exporting keys in various formats is provided in NuGet/npm packages separate from the core SSH functionality. Some key formats are only implemented in either the C# or TS libraries, not both. See also src/cs/SSH.Keys/README.md or src/ts/ssh-keys/README.md.

The following RFCs define the SSH protocol:

• RFC 4250 - SSH Protocol Assigned Numbers
• RFC 4251 - SSH Protocol Architecture
• RFC 4252 - SSH Authentication Protocol
• RFC 4253 - SSH Transport Layer Protocol
• RFC 4254 - SSH Connection Protocol
• RFC 4256 - Generic Message Exchange Authentication for SSH
• RFC 4716 - SSH Public Key File Format
• RFC 5647 - AES GCM for the SSH Protocol
• RFC 5656 - EC Algorithm Integration in SSH
• RFC 8308 - SSH Extension Negotiation