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
Famous quotes containing the word limitations:
“To note an artists limitations is but to define his talent. A reporter can write equally well about everything that is presented to his view, but a creative writer can do his best only with what lies within the range and character of his deepest sympathies.”
—Willa Cather (18761947)
“Much of what contrives to create critical moments in parenting stems from a fundamental misunderstanding as to what the child is capable of at any given age. If a parent misjudges a childs limitations as well as his own abilities, the potential exists for unreasonable expectations, frustration, disappointment and an unrealistic belief that what the child really needs is to be punished.”
—Lawrence Balter (20th century)
“The limitations of pleasure cannot be overcome by more pleasure.”
—Mason Cooley (b. 1927)