Using existing keys

Hi all,

We'd like to use certificates to ssh between machines in our network.
The machines concerned already have X.509 certificates and private keys
for use with openswan, and we would like to re-use these for ssh rather
than generate new ones with ssh-keygen.

I think all the files are in the right places (id_rsa, id_rsa.pub on the
client, and a copy of the client public key in authorized_keys2).
According to the server debug, there is a problem with the client public
key in authorized_keys2.  This was generated from the public key withthe
command openssl rsa -in privatekey.pem -pubout > publickey.pem

I generated a keypair with ssh_keygen for comparison purposes and there
is a noticable difference in the format as follows.

openssl-generated public key:

-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC4qgs3e4dyFv5jPawn8iWjPmJT
sJ7NCyadt2nKB35mJp5evWlfrbILDSk0NqOjAiA/aDOcrH/QeCto8gzYOapv7KYd
Lb0cfsnz+qhdgBucLC7ZguyTyrfomreaRTPyxEof5/VOOQiAVYby+y9wdNXws+Xd
tIqUfvQ2df4kJIEaxQIDAQAB
-----END PUBLIC KEY-----

ssh-keygen public key:

ssh-rsa
AAAAB3NzaC1yc2EAAAABIwAAAIEA9Ue+YGFwbpVML+4pbGcYS8rsO0xNbT3uXTJNAs2M2KN7KZLZF6ATjzgzrPe3f0f9QIqarqylxmdH4Lkg1Fv4YtxzNdr4J0iiHBULJ9WlBXz1ax2F/tRocG8Yx7GX3JpGqd9FzcA24kC9gahb99/2rJLadGRRsO4rT20hf+zt4+8= 

root@geddy

How can I get sshd to work with the former style of public key, or is
there any other workaround?  We're using 3.8.1 on Linux at both ends.

Antony