In cryptography

Cryptography

Cryptography is the practice and study of techniques for secure communication in the presence of third parties...

, the security parameter is a variable that measures the input size of the problem. Both the resource requirements of the cryptographic algorithm

Algorithm

In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...

 or protocol as well as the adversary

Adversary (cryptography)

In cryptography, an adversary is a malicious entity whose aim is to prevent the users of the cryptosystem from achieving their goal...

's probability of breaking security are expressed in terms of the security parameter.

The security parameter size n is usually expressed in unary representation

Unary numeral system

The unary numeral system is the bijective base-1 numeral system. It is the simplest numeral system to represent natural numbers: in order to represent a number N, an arbitrarily chosen symbol representing 1 is repeated N times. For example, using the symbol | , the number 6 is represented as ||||||...

(i.e. a n-long string of bits 1) so that the cryptographic algorithm execution efficiency can be polynomial-time in the length of the input size.

Typical security parameters:

• The length, in bits, of the key used in a cryptographic scheme.