The “Couldn’t agree a key algorithm” error in Git for Windows

When trying to perform any authentication-related operation in Git for Windows you may hit the wall with:

Couldn’t agree a key algorithm (available: list of available methods)

Some people says (here and here for example, but also in many other places) that this is due to your PuTTY not being up-to-date and ordering getting latest version of PuTTY as a cure. You’re lucky, if that works for you! :>

I wasn’t that lucky and it turned out that in case of my Git for Windows TortisePlink was actually the problem.

In a course of a short investigation (which resulted in writing this article) it turned out that TortoisePlink.exe:

  • used by me so far was from 1 ‎April ‎2014, ‏‎17:56:54, with 358 KB (367 464 bytes) size and
  • I have updated it to the version from ‎9 ‎August ‎2018, ‏‎00:40:16, having 558 KB (571 552 bytes).

The significant change of file size was not only an effect of update, but also probably a side-effect of removing .exe file compression from all PuTTy’s files that took place some years ago.

Updating TortoisePlink to newest version available was the only step that I had to undertake. Right after that I could update my local repositories again, with no authentication- or key algorithm-related problems.

Thus, it turned out that the solution is as easy as in case of PuTTY update, described above. The only difference was the fact that getting newest version of TortoisePlink isn’t that easy after all.

If neither update of PuTTy nor update of TortoisePlink solves your problem and you’re still getting “Couldn’t agree a key algorithm” error then take a look at this Stack Overflow question. In answers to it you may find some other clues and ideas.

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