I was absolutely floored when I found out that $100 million MBS trades are done by voice telephone call.
Now, the call is recorded, but still
no crypto, nothing. Yow.
Just for the historical explanation purposes:
For the telephone trading the primary line of defense is ANI:
http://en.wikipedia.org/wiki/Automatic_number_identificationStraight ANI is often strenghtened by either quick comparison with real time billing information or various SS7 tracing/call maintenance features.
http://en.wikipedia.org/wiki/Signalling_System_No._7While pikers trade with touch-tones the whales get service of the dedicated VIP staff. It is a form of biometric authentication, people employed in high-value account service have extraordinary auditory memory (or visual memory, for the in-person service).