convert putty key to openssh key

有的合作方给的是putty生成的私钥，为了方便使用需要
把putty格式的转化成openssh格式的pm@debian:~$ puttygen –helpPuTTYgen unidentified build, Jun 22 2012 15:52:56Usage: puttygen ( keyfile | -t type [ -b bits ] )[ -C comment ] [ -P ] [ -q ][ -o output-keyfile ] [ -O type | -l | -L | -p ]-t    specify key type when generating (rsa, dsa, rsa1)-b    specify number of bits when generating key-C    change or specify key comment-P    change key passphrase-q    quiet: do not display progress bar-O    specify output type:private             output PuTTY private key formatprivate-openssh
export OpenSSH private keyprivate-sshcom
export ssh.com private keypublic              standard / ssh.com public keypublic-openssh      OpenSSH public keyfingerprint         output the key fingerprint-o    specify output file-l    equivalent to `-O fingerprint’-L    equivalent to `-O public-openssh’-p    equivalent to `-O public’