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