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Dev Tunnels SSH Library

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

Feature Highlights

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.

Limitations

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.

C# (.NET Framework, .NET Core, .NET 6)

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.

TypeScript (Node.js or Browser)

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.

Packages

	C# NuGet package	TS npm package
SSH core protocol and crypto	`Microsoft.DevTunnels.Ssh`	`@microsoft/dev-tunnels-ssh`
SSH public/private key import/export	`Microsoft.DevTunnels.Ssh.Keys`	`@microsoft/dev-tunnels-ssh-keys`
SSH TCP connections and port-forwarding	`Microsoft.DevTunnels.Ssh.Tcp`	`@microsoft/dev-tunnels-ssh-tcp`

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.

Development

See README-dev.md.

SSH Algorithms Support

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.

Type	Algorithm Name	Status

key-exchange	`diffie-hellman-group16-sha512`	✔✔
key-exchange	`diffie-hellman-group14-sha256`	✔✔
key-exchange	`ecdh-sha2-nistp521`	✔
key-exchange	`ecdh-sha2-nistp384`	✔✔✔
key-exchange	`ecdh-sha2-nistp256`	✔✔
key-exchange	`curve25519-sha256`	?? [1]

public-key	`rsa-sha2-512`	✔✔✔
public-key	`rsa-sha2-256`	✔✔
public-key	`ecdsa-sha2-nistp256`	✔✔
public-key	`ecdsa-sha2-nistp384`	✔✔
public-key	`ecdsa-sha2-nistp521`	✔
public-key	`ssh-ed25519`	?? [1]
public-key	`*-cert-v01@openssh.com`	?? [2]

cipher	`aes256-cbc`	✔✔ [3]
cipher	`aes256-ctr`	✔✔
cipher	`aes192-cbc`	✔
cipher	`aes192-ctr`	✔
cipher	`aes128-cbc`	✔
cipher	`aes128-ctr`	✔
cipher	`aes256-gcm@openssh.com`	✔✔✔
cipher	`aes128-gcm@openssh.com`	✔
cipher	`chacha20-poly1305@openssh.com`	?? [1]

mac	`hmac-sha2-512`	✔✔
mac	`hmac-sha2-256`	✔✔
mac	`hmac-sha2-512-etm@openssh.com`	✔✔✔
mac	`hmac-sha2-256-etm@openssh.com`	✔✔

[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.

Key Format Support

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.

Key Format	Key Algorithm	Password Protection	Format Description
SSH public key	RSA ECDSA	N/A	Single line key algorithm name, base64-encoded key bytes, and optional comment. Files conventionally end with `.pub`.
PKCS#1	RSA	import only	Starts with one of: `-----BEGIN RSA PUBLIC KEY-----` `-----BEGIN RSA PRIVATE KEY-----`
SEC1	ECDSA	import only	Starts with: `-----BEGIN EC PRIVATE KEY-----`
PKCS#8	RSA ECDSA	✔	Starts with one of: `-----BEGIN PUBLIC KEY-----` `-----BEGIN PRIVATE KEY-----` `-----BEGIN ENCRYPTED PRIVATE KEY-----`
SSH2 C# only	RSA	✔	Starts with one of: `---- BEGIN SSH2 PUBLIC KEY ----` `---- BEGIN SSH2 ENCRYPTED PRIVATE KEY ----`
OpenSSH C# only	RSA ECDSA	✔	Starts with one of: `-----BEGIN OPENSSH PUBLIC KEY-----` `-----BEGIN OPENSSH PRIVATE KEY-----`
JWK TS only	RSA ECDSA	N/A	JSON with key algorithm name and parameters

References

The following RFCs define the SSH protocol:

goldenbull/dev-tunnels-ssh