Limitations
The DC-net protocol is simple and elegant. It has several limitations, however, some solutions to which have been explored in followup research (see the References section below).
1. Collision - If two cryptographers paid for the dinner, their messages will cancel each other out, and the final XOR result will be . This is called a collision, and allows only one participant to transmit at a time using this protocol. In a more general case, a collision happens as long as any even number of participants send messages. The measure suggested by David Chaum is to re-transmit the message once a collision is detected, but the paper does not explain exactly how to arrange the re-transmission.
2. Disruption - The cryptographer who last announces the bit has the advantage of manipulating the final result. For example, if he is dishonest, he can jam the protocol so that the final XOR result is always . This problem occurs because the original protocol was designed without using any public key technology; but as a downside, the protocol lacks reliable mechanisms to check whether participants honestly follow the protocol.
3. Complexity - The protocol requires pair-wise shared secret keys between the participants, which may be problematic if there are many participants. Also, though the DC-net protocol is "unconditionally secure", it actually depends on the assumption that "unconditionally secure" channels already exist between pairs of the participants, which is not easy to achieve in practice.
A related anonymous veto network algorithm computes the logical OR of several users' inputs, rather than a logical XOR as in DC-nets, which may be useful in applications to which a logical OR combining operation is naturally suited.
Read more about this topic: Dining Cryptographers Problem
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—James Thurber (1894–1961)
“That all may be so, but when I begin to exercise that power I am not conscious of the power, but only of the limitations imposed on me.”
—William Howard Taft (1857–1930)
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—Judith Viorst (20th century)