SSH from .NET Core support

[juzuluag]

During the work with a customer, discovered that .NET core doesn't contain SSH which was crucial for the development of the engagement. Using a 3rd party NuGet package (known as SSH.NET) was the workaround, which unfortunately is not well maintained and supported, which brings the following issues:

• Security:
  Lack of more/new secure encryption algorithms given the fact the github repository lacks continuous support.
• Asynchronous support:
  Current package is implemented using AMP (Asynchronous Programming Model), which is the legacy asynchronous implementation, compared to what most recent versions of dotnet .NET that supports – TAP (Task-based Asynchronous Pattern), which is what was used by customer.
• Lack of Documentation:
  It required to spend good amount of time reading SSH.NET repository, on how the package was implemented, look at some tests how those were written to have a good idea on how to consume the SSH client provided by the package.

it is very common to find SSH as a standard mechanism to communicate between services across different platform, which brings the issue here whether this should be considered as workable item.

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

Tagging subscribers to this area: @dotnet/ncl, @vcsjones
See info in area-owners.md if you want to be subscribed.

Issue Details

---

During the work with a customer, discovered that .NET core doesn't contain SSH which was crucial for the development of the engagement. Using a 3rd party NuGet package (known as SSH.NET) was the workaround, which unfortunately is not well maintained and supported, which brings the following issues:

• Security:
  Lack of more/new secure encryption algorithms given the fact the github repository lacks continuous support.
• Asynchronous support:
  Current package is implemented using AMP (Asynchronous Programming Model), which is the legacy asynchronous implementation, compared to what most recent versions of dotnet .NET that supports – TAP (Task-based Asynchronous Pattern), which is what was used by customer.
• Lack of Documentation:
  It required to spend good amount of time reading SSH.NET repository, on how the package was implemented, look at some tests how those were written to have a good idea on how to consume the SSH client provided by the package.

it is very common to find SSH as a standard mechanism to communicate between services across different platform, which brings the issue here whether this should be considered as workable item.

Author:	juzuluag
Assignees:	-
Labels:	area-System.Net.Security, untriaged
Milestone:	-

[wfurt]

related to #40424 and #31437. We may choose to contribute to https://github.com/sshnet/SSH.NET and perhaps bring it under https://dotnetfoundation.org/ umbrella.

[antonfirsov]

Triage: we want to see how much demand is from community, and consider it in the future. Please upvote top post if interested.

[karelz]

Previously we had interest in:

• Incorporating SSH client lib in corefx?  #17188
• Related: Support of SFTP and SCP #31437

[vcsjones]

I think @tmds made or started an SSH client library and noted that there are some possible missing cryptographic pieces, particularly around DiffieHellman, if I recall correctly. SSH needs the "raw" DiffieHellman secret where we don't provide it. SSH.NET gets around this by implementing a lot of the cryptography by hand or borrowing from BouncyCastle.

Is that right @tmds?

[tmds]

That's right. There is no API that returns the shared secret. And if I remember correctly, Windows itself doesn't provide one.

After trying the managed implementation on top of .NET crypto APIs, I did another prototype that wraps libssh. The code is at https://github.com/tmds/Tmds.Ssh. (The managed implementation is under the release/v0.1 branch.)

[iSazonov]

/cc @SteveL-MSFT Could you please share thoughts on the possibility of implementing this request?

[vcsjones]

Windows itself doesn't provide one.

I think this is possible with BCryptDeriveKey and specifying BCRYPT_KDF_RAW_SECRET. It's only on Windows 10+, and would be somewhat tricky to make work as it's a BCrypt API, whereas the ECDiffieHellmanCng implementation is built on top of NCrypt (to support CngKey and the like). For whatever reason the NCryptDeriveKey does not support raw values.

But I digress.

[vcsjones]

To follow up on raw DH, .NET 8 has DeriveRawSecretAgreement so the D-H blocker has been removed.