Re-using RSA1 keys as RSA

[Dan Kaminsky]

Markus Friedl wrote:

>On Thu, Aug 21, 2003 at 09:10:13PM -0700, Frank Cusack wrote:
>  
>
>>Is there a security issue with turning an RSA1 key into an RSA key?  One
>>might want to do this, e.g., to move to protocol 2 without having to
>>update authorized_keys files.
>>    
>>
>
>in protocol 1 rsa keys are used for encryption,
>in protocol 2 they are used for signatures.
>  
>
Markus--

    In protocol 2, the RSA public key verifies a signature, as in 
protocol 1, a RSA public key encrypts a token.     I'm not sure, but the 
only difference between the two may very well be the source of the token 
being operated upon -- SSHv1 has the client generate random data; SSHv2 
has the server generate and hash it.  Either way, client + pubkey 
authenticates server + privkey.

    I'm not saying it's safe to dual-purpose RSA; I'm just not entirely 
sure I've seen evidence it's dangerous to multipurpose the same RSA 
key.  Have you seen any evidence to the contrary?

--Dan