In step 203, the signature key generator 123 uses {HEAD ~ a hashing function} to generate a signature key for {TAIL ~ the fingerprint} 
In step 203 , the signature key generator 123 uses { HEAD ~ a hashing function } to generate a signature key for { TAIL ~ the fingerprint }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL