git - Jenkins: what is the correct format for private key in Credentials

Question

I'm creating a job in Jenkins 2.152 running on Windows Server 2016 which needs to pull from a git repo hosted on bitbucket.org. I tested the ssh key through git-bash so I know it works and there is no passphrase. When I try to use the very same private key with Jenkins I get an error message.

Failed to connect to repository : Command "git.exe ls-remote -h 
[email protected]:mygroup/myrepo HEAD" returned status code 128:
stdout: 
stderr: Load key 
"C:\Users\JE~1\AppData\Local\Temp\ssh2142299850576289882.key": invalid format 
[email protected]: Permission denied (publickey). 
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

The Credentials are set up as

 scope: Global
 user: git
 Private Key -> Enter Directly -> copy and past - generated by ssh-keygen -t rsa in gitbash
 Passphrase: empty
 ID: empty
 description: bitbucket.org

I noticed that on another Windows Jenkins server the private key has a different number of characters per line

Does anybody know what is the expected format of Private Key in Jenkins Credentials? Or maybe there is something else that I could check.

Any help is greatly appreciated.

Answer 1

Check the version of Git for Windows that you are using: Starting 2.19.2, it comes with OpenSSH v7.9p1 (from 7.7 before)

And... openssh 7.8 just changed the default ssh-keygen format, from a classic PEM 64-chars, to an OPENSSH one 70 chars!

Only ssh-keygen -m PEM -t rsa -P "" -f afile would generate the old format (-m PEM)

ssh-keygen(1):

write OpenSSH format private keys by default instead of using OpenSSL's PEM format.

The OpenSSH format, supported in OpenSSH releases since 2014 and described in the PROTOCOL.key file in the source distribution, offers substantially better protection against offline password guessing and supports key comments in private keys.
If necessary, it is possible to write old PEM-style keys by adding "-m PEM" to ssh-keygen's arguments when generating or updating a key.