I strongly discourage anyone from using PuTTY, not for this reason, but for its weird and nonstandard handling of SSH keys.

The last time I tried to help someone get it set up on a windows PC, totally normal ssh2 rsa 2048 and 4096 bit public/private key pairs created with openssh had to be converted into some other weird format before they could get public/private key auth working.

Why the developers of putty felt they needed to deviate from standard ssh2-rsa pub/privkey formats is a mystery to me.