I've obtained a developer certificate and am now trying to sign my .sis with it, however it's giving error.

Could not verify signature with known algorithm, exiting.
encryption error, not a DSA certificate.
I've tried using the -cr paramater in case it was using RSA not DSA but that got the error

or:0607907F:digital envelope routines:EVP_PKEY_get1_RSA:expecting an rsa keye
r:0D0680A8:asn1 encoding routines:ASN1_CHECK_TLEN:wrong tagencryption error,
not load ApeKey.key.
Am I right in thinking all you need to do when switching from self certified to developer certificate certified is to switch the .cer file from the self certified one to the developer one? If not guess my problem is there, the documentation seems totally unclear on this.