Accessing a hash algorithm by manipulating the HashName property is not supported on this platform.

[alvaromolinaGL]

Hi, I am using the library to send some files through an sftp, I am connecting to the site via the SftpClient class:

var client = new SftpClient(host, port, username, password);

client.Connect();
client.UploadFile(zipFile, outPath);
client.Disconnect();

This code is running in an azure function, it was working fine but it stopped working back in May and its now throwing this message:

Accessing a hash algorithm by manipulating the HashName property is not supported on this platform. Instead, you must instantiate one of the supplied subtypes (such as HMACSHA1.)

Any ideas??

Thanks.

[IgorMilavec]

Can you provide the call stack of the exception?

[dd-morphi]

Hi,
Recently I've hit an issue with the same error message but in a different scenario.
My code is connecting to devices through SSH. One of those devices is an older Linux.
When connecting to it on Windows with .net5 it throws the exception:

System.PlatformNotSupportedException: Accessing a hash algorithm by manipulating the HashName property is not supported on this platform. Instead, you must instantiate one of the supplied subtypes (such as HMACSHA1.)
   at System.Security.Cryptography.HMAC.HashFinal()
   at Renci.SshNet.Security.Cryptography.HMACSHA1.HashFinal()
   at System.Security.Cryptography.HashAlgorithm.CaptureHashCodeAndReinitialize()
   at System.Security.Cryptography.HashAlgorithm.ComputeHash(Byte[] buffer)
   at Renci.SshNet.Session.SendMessage(Message message)
   at Renci.SshNet.Session.Connect()
   at Renci.SshNet.BaseClient.CreateAndConnectSession()
   at Renci.SshNet.BaseClient.Connect()

I was trying to debug your library and discovered that the issue is on this device because it returns the only hash algorithm hmac-sha1-96. It looks that your library on netstandard2.0 has an issue with this. When tried with framework it works.

I reproduced the issue with Ubuntu by adding the line MACs hmac-sha1-96 to /etc/ssh/sshd_config and restarting the sshd service.

The easiest workaround for it is removing FEATURE_HMAC_SHA1 from the list of DefineConstants and then rebuilding it. It uses then SshNet.Security.Cryptography which works correctly in this scenario.

---

I was looking also at your implementation of Renci.SshNet.Security.Cryptography.HMACSHA1 and the strange thing is that on netstandard2.0 it sees HMAC as the base implementation of HashFinal not HMACSHA1

When analyzing the .net implementation it looks that this error message is only thrown on the usage of HMAC methods.
I copied Renci.SshNet.Security.Cryptography.HMACSHA1 code to .net5.0 program and it works correctly.

I hope it helps somehow to fix it

[alvaromolinaGL]

That is exactly the error message I am seeing, it's throwing it when trying to connect to the sftp.

at System.Security.Cryptography.HMAC.HashFinal()
at Renci.SshNet.Security.Cryptography.HMACMD5.HashFinal()
at System.Security.Cryptography.HashAlgorithm.CaptureHashCodeAndReinitialize()
at System.Security.Cryptography.HashAlgorithm.ComputeHash(Byte[] buffer)
at Renci.SshNet.Session.SendMessage(Message message)
at Renci.SshNet.Session.Connect()
at Renci.SshNet.BaseClient.CreateAndConnectSession()
at Renci.SshNet.BaseClient.Connect()

How can I. change the DefineConstants?

[dd-morphi]

I have changed it like here dd-morphi@9d3387e?branch=9d3387e1d6b406c215a160d2bc0f0bb338c39f6f for netstandard2.0
Then I rebuild the library and in csproj instead of

  <ItemGroup>
    <PackageReference Include="SSH.NET" Version="2020.0.1" />
  </ItemGroup>

I put

  <ItemGroup>
    <PackageReference Include="SshNet.Security.Cryptography" Version="1.3.0" />
    <Reference Include="Renci.SshNet">
      <HintPath>..\Renci.SshNet.dll</HintPath>
    </Reference>
  </ItemGroup>

with reference to compiled library

[IgorMilavec]

This seems to be the problem mentioned in dotnet/runtime#22929.
@dd-morphi do I understand correctly that the issue is fixed in SshNet.Security.Cryptography and you could fix the error by backporting this class to SshNet?
@drieseng can you please help determine the appropriate course of action: should the changes be backported to SshNet or should crypto functionality be completely removed from SshNet in favor of using the SshNet.Security.Cryptography?

[dd-morphi]

@IgorMilavec backporting to SshNet.Security.Cryptography helps, but SSH.NET uses System.Security.Cryptography.HMACSHA1 in two places:

1. for "hmac-sha1" where it creates new System.Security.Cryptography.HMACSHA1(key)
2. for "hmac-sha1-96" where it derives from public class HMACSHA1 : System.Security.Cryptography.HMACSHA1

The first works correctly always, the second fails with this strange error message on .net5.0. (it looks like base keyword instead of parents HMACSHA1.HashFinal() method finds grand parents method HMAC.HashFinal())

[Ronn1e-D]

Same here! Using on Azure Function v3 (netcoreapp3.1), but with a specific SFTP server. I'm connecting with 3 different SFTP servers, 2 work flawlessly and 1 is failing with this exact error.

System.PlatformNotSupportedException: Accessing a hash algorithm by manipulating the HashName property is not supported on this platform. Instead, you must instantiate one of the supplied subtypes (such as HMACSHA1.) at System.Security.Cryptography.HMAC.HashFinal() at Renci.SshNet.Security.Cryptography.HMACSHA1.HashFinal() at System.Security.Cryptography.HashAlgorithm.CaptureHashCodeAndReinitialize() at System.Security.Cryptography.HashAlgorithm.ComputeHash(Byte[] buffer) at Renci.SshNet.Session.SendMessage(Message message) at Renci.SshNet.Session.Connect() at Renci.SshNet.BaseClient.CreateAndConnectSession() at Renci.SshNet.BaseClient.Connect() at D365.AzureFunctions.Handlers.SFTPHandler.UploadFile(Stream fileStream,String filename,String remoteFilePath)

Hoping for a permanent solution :) I really don't want to switch to another package.

[Ronn1e-D]

I can confirm that the solution provided by @dd-morphi works. Thanks for that :)

[malhotrar]

Hitting the same issue running .net5 on windows. What is the recommended course of action here? I'm not super thrilled about having to package a custom version here similar to @dd-morphi, as I use this in an enterprise ETL tool.

@drieseng - is there a timeline for a resolution?

[lawhorkl]

I tried @dd-morphi 's solution and its worked for us. I'd be willing to put a PR up if it would be merged in relatively soon.

Haven't had a release for a little while as well.

[Aethon]

It was good to find this discussion here, since we could not get past connecting with our client's SFTP server. We started down the path of this workaround, but were deeply unsatisfied with maintaining our own copy of the assembly. I poked a little and found an easier workaround that uses the published package:

        var info = new ConnectionInfo(
            "host.com",
            22,
            "user1",
            new PasswordAuthenticationMethod("user1", "secret_password")
        );
        info.HmacAlgorithms["hmac-sha1"] =
            new HashInfo(160, k => new SshNet.Security.Cryptography.HMACSHA1(k));
        info.HmacAlgorithms["hmac-sha1-96"] =
            new HashInfo(160, k => new SshNet.Security.Cryptography.HMACSHA1(k, 96));
        info.HmacAlgorithms["hmac-md5"] =
            new HashInfo(128, k => new SshNet.Security.Cryptography.HMACMD5(k));
        info.HmacAlgorithms["hmac-md5-96"] =
            new HashInfo(128, key => new SshNet.Security.Cryptography.HMACMD5(key, 96));

In our case, we only had to override the MD5 macs, but as many (or all) of the crypto algorithms can be fixed up via the connection info. Super nicely designed.

HTH someone else until the bug is fixed in a release, and thanks to the maintainers of this sweet library.

[menees]

Thanks, @Aethon! Your workaround was very helpful! I looked at the default HmacAlgorithms set by ConnectionInfo.cs, and I extended your example code to override them all with concrete implementations instead of using the CryptoAbstraction defaults.

var info = new ConnectionInfo(
	"host.com",
	22,
	"user1",
	new PasswordAuthenticationMethod("user1", "secret_password")
);
IDictionary<string, HashInfo> hmacAlgorithms = info.HmacAlgorithms;
hmacAlgorithms["hmac-md5"] = new HashInfo(128, key => new SshNet.Security.Cryptography.HMACMD5(key));
hmacAlgorithms["hmac-md5-96"] = new HashInfo(128, key => new SshNet.Security.Cryptography.HMACMD5(key, 96));
hmacAlgorithms["hmac-sha1"] = new HashInfo(160, key => new SshNet.Security.Cryptography.HMACSHA1(key));
hmacAlgorithms["hmac-sha1-96"] = new HashInfo(160, key => new SshNet.Security.Cryptography.HMACSHA1(key, 96));
hmacAlgorithms["hmac-sha2-256"] = new HashInfo(256, key => new SshNet.Security.Cryptography.HMACSHA256(key));
hmacAlgorithms["hmac-sha2-256-96"] = new HashInfo(256, key => new SshNet.Security.Cryptography.HMACSHA256(key, 96));
hmacAlgorithms["hmac-sha2-512"] = new HashInfo(512, key => new SshNet.Security.Cryptography.HMACSHA512(key));
hmacAlgorithms["hmac-sha2-512-96"] = new HashInfo(512, key => new SshNet.Security.Cryptography.HMACSHA512(key, 96));
hmacAlgorithms["hmac-ripemd160"] = new HashInfo(160, key => new SshNet.Security.Cryptography.HMACRIPEMD160(key));
hmacAlgorithms["hmac-ripemd160@openssh.com"] = new HashInfo(160, key => new SshNet.Security.Cryptography.HMACRIPEMD160(key));