I'm experiencing this issue for the first time, after my coworker updated all Jenkins plugins. git-client was upgraded to v1.18.0. I'm not sure what version was previously installed.
Keys without passwords work fine; keys with passwords no longer work.
If I log into the shell account for the Jenkins tomcat user, I see the following message echoed to the screen whenever Jenkins attempts to verify the Git credentials:
"Enter passphrase for key '/home/tomcat/tomcat/temp/ssh8175827570904316216key':
This problem persists in git-client versions 1.18 and 1.19. I'm not sure what version was installed when passwords seemed to work properly.
I'm using Jenkins 1.622 on Ubuntu 14.04.3 LTS, and Jenkins 1.617 on Yosemite. My repositories are hosted on GitHub.