Abstract
This chapter explains the basics of cryptography, while a description of image encryption. It provides a survey of the state of the art in Joint Photographic Experts Group (JPEG) crypto-compression, designed as a solution to this problem. The chapter illustrates the challenge of image processing in the crypto-compressed domain, notably with respect to one of the first proposed methods, involving the recompression of crypto-compressed images. A secret key is used as the initialization seed for a cryptographically secure pseudo-random number generator to generate a pseudo-random binary sequence, called the encryption stream, of the same size as the message to be encrypted. Image encryption methods must verify two properties: format conformity and size preservation. The chapter presents a state of the art of the broad categories of crypto-compression methods that are compatible with JPEG format, with examples selected on the basis of performance and diversity.