Cryptography Reference
In-Depth Information
to develop research agendas explicitly motivated by social concerns such
as privacy and anonymity. These, however, coexisted with more conserva-
tive approaches that sought to define the foundations of the field in purely
mathematical terms, motivated only by scientific needs for internal coher-
ence and objectivity. Finally, the relationship of cryptography to steganog-
raphy remained unsettled. The mathematical manipulation of binary digits
as an abstract quantity seemed to imply the chains that bound information
to its material substrate had been finally vanquished. Yet the public-key
cryptography framework generated surprising new possibilities and chal-
lenges for information hiding.
I begin by outlining the case for the public-key paradigm as argued by
Diffie and Hellman in “New Directions” and its first successful realization
by Rivest, Shamir, and Adleman. I then review the main episodes of the
“crypto wars,” as well as some of the defining research programs that
emerged in the 1990s, including Gustavus Simmons's “Science of Informa-
tion Integrity,” Oded Goldreich's quest for proper foundations, and David
Chaum's inquiry into authentication and anonymity.
Decentralized Cryptography
The problem of key distribution was, in Diffie and Hellman's analysis,
the
central problem to overcome if electronic networks were to fulfill their
potential for business:
In order to use cryptography to insure privacy, however, it is currently necessary for
the communicating parties to share a key which is known to no one else. This is
done by sending the key in advance over some secure channel, such as private
courier or registered mail. A private conversation between two people with no prior
acquaintance is a common occurrence in business, however, and it is unrealistic to
expect initial business contacts to be postponed long enough for keys to be trans-
mitted by some physical means. The cost and delay imposed by this key distribution
problem is a major barrier to the transfer of business communications to large tele-
processing networks.
4
Using traditional (secret key) cryptography, in a computer network
comprising a large number of users (say,
n
), each pair of users must estab-
lish a common key (see figure 3.1). Doing so requires a quadratic (
n
2
)
number of key pairs, because each of the
n
users needs to establish a key
with
n
- 1 other users, along with a corresponding number of communica-
tion rounds between users to establish the keys. Diffie and Hellman argued
