Cryptography Reference
In-Depth Information
It is against this background of a seemingly familiar yet potentially
mysterious object that the “discovery” of a digital analogue would take
place. The process would involve defining a
model
, some specification of
the multidimensional physical artifact that would aim to capture the char-
acteristics deemed most pertinent to the digital context. In this chapter, I
tease out the gradual construction of the cryptographic signature model,
a process that largely took place without explicit recognition of the rep-
resentational nature of models.
Beginning with Diffie and Hellman's initial suggestion that public-key
cryptography could provide the basis for a suitable “equivalent” to hand-
written signatures, I review how cryptographers came to define the services
that cryptographic signatures would be expected to provide, namely
aut-
hentication
,
integrity
, and
non-repudiation
. I also review the gradual elabora-
tion of a solution to the problem of secure and efficient distribution of
public keys, that of
public-key infrastructures
(PKI).
Another window on the modeling practices of the cryptographic com-
munity is provided by an activity that extends cryptographic work beyond
the mere design of digital analogues to paper-based protocols. The defini-
tion of signatures as a cryptographic object with specific mathematical
properties opens the possibility for the creation of entirely new types of
signatures with unheard-of security properties. I describe some of these
new kinds of signatures and the real-world scenarios provided by crypto-
graphers to justify their design. Finally, the various
proof models
under
which the security of cryptosystems is mathematically proved are discussed
in chapter 7.
My goal here is to map as precisely as possible the contours of digital
signatures as an object, usable by cryptographers, users, and the legal
process. Which problems did the model solve for each of these groups?
Which features of the “real world” artifact did the model encompass, and
which were deemed irrelevant? What disciplinary assumptions were
brought to bear on the model? How did the practical logic of cryptographic
work constrain the scope of the model? How did cryptographers experience
and debate the relationship of mathematical work to the “real world”? A
precise picture of digital signatures as eventually defined by the crypto-
graphic community will provide the necessary foundation from which to
investigate the reception of this object by the legal community in subse-
quent chapters.
