Putty with ssh key authentication

When using ssh keys generated by puttygen.exe, I receive a “Server refused our key” error. Then I found out that the error-proof way is this: generate ssh key pairs under Linux, and then convert the private key into putty format using puttygen.exe.

Procedures

  • change ~/.ssh directory and authorized_keys permissions
chmod 700 .ssh
chmod 600 authorized_keys
  • generate the key pair. Most tutorials seems to prefer to use dsa format
ssh-keygen -t dsa
  • use the default file name and enter the passphrase
  • add the public key to authorized_keys
cat id_dsa.pub >> .ssh/authorized_keys
  • copy the private key (id_dsa) to the local windows machine. Then use puttygen.exe to convert the key and save it to a separate private key

Then configure the putty to use the new private key.

Additional notes

Under Debian Lenny, I don’t need to make any changes to /etc/ssh/ssh_config to make putty auto authentication work.

The putty does not authenticate with the public key, but with .ssh/authorized_keys instead, that’s why the public key should be copied to authorized_keys file.

References

ssh – authorized_keys HOWTO for some fundamentals

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