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and Bob share some secret information without revealing it to each other. The researchers
discovered that this problem is a re-statement of the Socialist Millionaire Problem where
two millionaires want to know whether they are equally wealthy without revealing to each
other the quantity of their wealth.
The mathematics behind this problem rely on a technique called a zero-knowledge proof .
A zero knowledge proof allows someone to attest to the correctness of a statement without
providing any additional information about the said statement. The details and proof of
OTR's zero-knowledge proofs are beyond the scope of this topic and described in detail in
(Alexander 2007).
The implication of using the Socialist Millionaire Problem in OTR is that Alice can ask
Bob a specific question that only Bob would know. If Mallory is masquerading as Bob
and if Alice chose a good question to which Mallory doesn't know the answer, Mallory
won't gain any additional information about the answer if she guesses wrong. For ex-
ample, Alice asks Mallory, pretending to be Bob, who her favorite guitarist is. Bob knows
that Alice is a Who fan and the answer is none other then Pete Townshend. Mallory does
not know this detail so she provides an admirable, but incorrect, answer of Jimmy Page.
Alice will see the protocol fail and know that Bob is not who he appears to be. But Mal-
lory will not know any other information about the answer other than that Jimmy Page is
not correct. However, it is too late for Mallory because Alice no longer trusts her and ter-
minates the connection.
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