The following steps can help to generate such key with PuTTY KeyGen (for example)
- Open tool:
- In Parameters section, select SSH-2 RSA and number of bits 1024/2048.
- Click Generate button in Actions section and move mouse over blank area as tool requires.
- In Key section, save your private and public keys.
- Click Conversions in tool menu.
Select Export OpenSSH key and then save this key to file.
- Open file and copy this key. Paste it into related textarea on source(target) config page.