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Key exchange failed FIPS-certified AES implementation not available

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by (120 points)
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I'm getting the following error on a widow 2003 server with FIPS enabled. It works fine on a window 7 machine.

Rebex.Net.SftpException: Key exchange failed. ---> Rebex.Net.SshException: Key exchange failed. ---> System.Security.Cryptography.CryptographicException: FIPS-certified AES implementation is not available.
   at Rebex.Security.Cryptography.SymmetricKeyAlgorithm.N()
   at Rebex.Security.Cryptography.SymmetricKeyAlgorithm.CreateEncryptor()
   at Rebex.Security.Cryptography.WU.T()
   at Rebex.Net.SshSession.ZR(Byte[] A)
   --- End of inner exception stack trace ---
   at Rebex.Net.SshSession.ZR(Byte[] A)
   at Rebex.Net.SshSession.YR()
   at Rebex.Net.SshSession.Negotiate()
   at Rebex.Net.Sftp.EEB.ZR(SDB A)
   at Rebex.Net.Sftp.KL(String A, Int32 B, SshParameters C, SDB D)
   --- End of inner exception stack trace ---
   at Rebex.Net.Sftp.KL(String A, Int32 B, SshParameters C, SDB D)
   at Rebex.Net.Sftp.JL(String A, Int32 B, SshParameters C)
   at sftp_connect.Program.uploadFile(String _database, String _localPath, String _fileName) in ...
by (147k points)
edited

Please determine whether bool forceManagedAes = Rebex.Security.Cryptography.CryptoHelper.ForceManagedAes; returns true or false and let me know!

by (120 points)
edited

Where is cryptohelper defined?

by (147k points)
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It's in Rebex.Common.dll assembly, Rebex.Security.Cryptography namespace.

by (120 points)
edited

It's false

1 Answer

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by (147k points)
edited

It looks like the version of .NET Framework 3.5 on your Windows 2003 Server has a memory leak bug in AesCryptoServiceProvider class. Rebex SFTP normally works around this by using RijndaelManaged class instead, but this can't be done in FIPS-enabled mode because RijndaelManaged doesn't use a certified AES implementation.

Under these cirsumstances, Rebex SFTP should actually disable AES while negotiation the SSH connection, but due to a bug in a detection routine, this doesn't happen.

There are three ways to solve the issue:

  • Install the hotfix for the .NET AesCryptoServiceProvider bug (this is the recommended solution)
  • Disable AES before connecting to the server using the following code: sftp.Settings.SshParameters.EncryptionAlgorithms &= ~SshEncryptionAlgorithm.AES; (where sftp is an instance of Sftp class)
  • Download a hotfix for Rebex SFTP that disables AES automatically under these circumstances.
by (120 points)
edited

Problem solved after applying the hotfix, thanks

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