Cryptography Reference
In-Depth Information
the algorithm consists of a set of arbitrary computational steps that are executed
sequentially.
Algorithm 1.1
The notation used to describe algorithms.
(input parameters)
...
computational step
...
(output parameters)
If more than one entity is involved in an algorithm (or the computational
procedure it defines, respectively), then one is in the realm of protocols.
2
As
suggested in Definition 1.2, a protocol can be viewed as a distributed algorithm.
Definition 1.2 (Protocol)
A
protocol
is a distributed algorithm in which two or
more entities take part.
Alternatively, one could also define a protocol as a distributed algorithm in
which a set of entities takes part. In this case, it becomes immediately clear that
an algorithm also represents a protocol, namely one that is degenerated in a certain
sense (i.e., the set consists of only one entity). Hence, an algorithm can always be
viewed as a special case of a protocol. The major distinction between an algorithm
and a protocol is that only one entity is involved in the former, whereas typically
two or more entities are involved in the latter. This distinguishing fact is important
and must be kept in mind when one talks about algorithms and protocols (not only
cryptographic ones).
Similar to an algorithm, a protocol may be
deterministic
or
probabilistic
(de-
pending on whether the protocol internally uses and takes advantage of random val-
ues). In fact, many protocols overviewed and discussed in this topic are probabilistic
in nature.
In this topic, we are mainly interested in cryptographic algorithms and proto-
cols as suggested in Definitions 1.3 and 1.4.
Definition 1.3 (Cryptographic algorithm)
A
cryptographic algorithm
is an algo-
rithm that employs and makes use of cryptographic techniques and mechanisms.
Definition 1.4 (Cryptographic protocol)
A
cryptographic protocol
is a protocol
that employs and makes use of cryptographic techniques and mechanisms.
2
The term protocol originates from diplomacy.
