[Taler] Meaning of XORed hashes in the Exchange API

[Jonathan Krebs]

Hi again :)

I do not understand the use of the fields denominations_sig and 
denominations[i].hash in the /keys response:

the wallet-core repo does not seem to use these at all, all denom 
pubkeys are signed individually, and as the hashes are combined with 
xor, this does not protect against tampering with the list. (once enough 
denominations exist, they can be combined linearly to achieve arbitrary 
hash values)

Please give me a hint about intended use or history of those, or about 
my misunderstanding :)

Thanks in advance,
thejonny