I've always used wpa-passphrase in the /etc/network/interfaces file with a string value representing a LOOOOOONG password...in fact, so long it's called a passphrase instead of a password.
The syntax would be something like:
OTOH, I've never used wpa-psk in the file because I've always considered that to be the hex key that was generated from the passphrase. That key is 64 hex characters long NOT surrounded by quotes:
Looking around these forums, this site, other sites, numerous Google Search results, etc etc I see many many people using wpa-psk as if it were the holder of the passphrase instead (or maybe even in addition to!) a hex key.
This is strange.
In any case, I've made a couple posts here referencing a working /etc/network/interfaces file that uses wpa-passphrase with a multiword quoted string as its argument so I certainly know THAT works.
Bottomline question: Does using instead wpa-psk with a multiword quoted string ALSO work?