Convert RSA public key to the right format

Question

I need to send a public key to my bank. I'm using CoreFTP which allows the generation of keys using RSA. It says that it generates "OpenSSH compatible certificates [sic]" when you press the generate keys button.

The keys it generates have

-----BEGIN RSA PUBLIC KEY-----

at the start (and then the key and then an end marker).

My bank rejects my public key and says it should begin ssh-rsa.

I suspect "RSA" and "OpenSSH" have variations that neither end are being clear about what they generate/expect.

How can I convert my key from the format the CoreFTP is providing to the format my bank wants?

Answer 1

I believe the reason is that the CoreFTP is actually generating OpenSSL keys and not OpenSSH formatted ones.

Perhaps your question is already answered on Stackoverflow?

https://stackoverflow.com/q/1011572/643314

From Victor Matare on SO:

You can do the same with ssh-keygen:

ssh-keygen -f pub1key.pub -i -m PKCS8

will read the public key in openssl format from pub1key.pub and output it in openssh format.