I haven't studied the key exchange for export ciphers, but I wonder if it would be possible to save a copy of the signature on the 512-bit key and replay it lat

I haven't studied the key exchange for export ciphers, but I wonder if it would be possible to save a copy of the signature on the 512-bit key and replay it later. If that's possible, then disabling export ciphers after the attacker has already a copy of the signed 512-bit key is not enough; the certificate has to be revoked (and we all know how reliable certificate revocation is).