Can you hash an ssh key to generate a symmetric password? Let's say you need a 256 bit password but all you have is an SSH key.  Can you securely transform the SSH key into a symmetric password via a hashing function?  What would be a good choice for a hash function?
Yes... Assuming:


That they were generated using enough entropy (probably yes if they were generated securely)
That they are only used for this purpose (I'd guess you can hash private key, but then as soon as it is compromised, your key is too)
It isn't done using public key, if that key is then published


As for hash function, any hash that isn't broken will do.