## Easter egg

is a hidden feature in a program that has been voluntarily placed by the developer(s) for personal reasons. A complex set of sequences triggers the Easter egg. Easter eggs are always for entertainment and never malwares. Famous Easter eggs are the flight simulation in the credits of Microsoft Excel or the pinball application in Microsoft Word 97. For more information see http://www.eeggs.com/faq.html

## Eavesdropping

is the fact to listen to a message that is not intended to you. This is typical when spying a databus, a telephone line, or a wireless connection.

## ECash

was a DigiCash software based payments systems using any computer network.

## ECB (Electronic Code Block)

See Block cipher

## ECC

See Elliptic Curve Cryptosystem

## ELGAMAL

this type of cryptosystems is based on the discrete logarithm problem. It is in use for encryption, and signature. It can be used with modular or elliptic curve exponentiation discrete logarithm problem.

For equivalent key length, it is as secure as RSA. It needs randomness. It is slower than RSA. Message expands by two regarding RSA.

## Elliptic Curve Cryptosystem

is an asymmetric cryptosystem based on the Elliptic Curve Logarithm problem. This category of cryptosystem offers the advantage to use smaller size of keys (160 bits versus 1024 for RSA) and simpler implemented operations (XOR and Rotation versus exponentiation). Therefore, consumer electronics is very interested by ECC.

## Elliptic Curve Logarithm Problem

Given a point G on an elliptic curve with order r, and another point Y on the curve, find a unique x less than r such that G=Y.x

The difficulty to solve this problem is the basic assumption of ECC.

## Encryption

Process that aims to transform, by using secret conventions, intelligible information into non-intelligible information for third party. The process is also used to perform the reverse operation. Some of the most famous encryption algorithms are DES, IDEA, and RSA.

Encryption often uses two basic complementary concepts: confusion and diffusion. Confusion consists of scrambling up a message. Diffusion involves taking one part of the message and modifying another part of the message so that each part of the final message depends on many other parts of the message.

## Entropy

is, according to SHANNON, the number of useful bits of information in a stream.

## ESIGN

(Electronic Signature In Global and National Commerce Act). This law S761 has been adopted by USA on June 30, 2000. Electronic signatures became as legally binding as printed signatures. The legislation does not specify how they should be implemented, how their validity should be ensured.

## Exhaustive key search

## Exponential key agreement

See DIFFIE