Today I learnt about FIPS and SHA1

Sha-familySystem.InvalidOperationException: This implementation is not part of the Windows Platform FIPS validated cryptographic algorithms. at System.Security.Cryptography.SHA1Managed..ctor() at ....

When I say “learnt”, it was more about reading documents to determine what happened to cause the above error.

I suspect either of these:

  1. Microsoft have released a new schannel.dll which removes and/or breaks SHA1 functionally.
  2. The Group Policy setting “System cryptography: Use FIPS compliant algorithms for encryption, hashing, and signing” has been enabled.

My quick “fix” was to change the application to use a different hashing algorithm.