No need to compile stuff. You can do the same with ssh-keygen
:
ssh-keygen -f pub1key.pub -i
will read the public key in openssl format from pub1key.pub
and output it in OpenSSH format.
Note: In some cases you will need to specify the input format:
ssh-keygen -f pub1key.pub -i -mPKCS8
From the ssh-keygen docs (From man ssh-keygen):
-m key_format Specify a key format for the -i (import) or -e (export) conversion options. The supported key formats are: “RFC4716” (RFC 4716/SSH2 public or private key), “PKCS8” (PEM PKCS8 public key) or “PEM” (PEM public key). The default conversion format is “RFC4716”.