At the moment, Rebex supports the following private key formats:
1) PKCS #8 format.
2) PuTTY PPKv2 format.
3) OpenSSH/OpenSSL SSLeay format.
PGP's .asc files are not supported, but if you find a way to convert it to one of the above formats, it should work. We will look into this format as well and let you know what we find.