one-tenth as large. Thus, the choice of encryption method depends on the intended application. The most widespread symmetric system is the data encryption standard (DES), which was developed by IBM in the mid-1970s. The DES used a key size of 56 bits. With recent hardware developments, however, a 56-bit key size space can be entirely searched by advanced machines within hours or even minutes. For this reason, the National Institute of Standards and Technology (NIST) initiated the development of the advanced encryption standard (AES), which supports 128- to 256-bit keys. Moreover, unlike the development of DES, the AES design process is open to the public. A key length of 128 bits is considered secure. IPsec applies AES encryption. Security 6.10.3 ELECTRONIC SIGNATURES Electronic signatures enable the recipient of information to verify the authenticity of the information's origin, and also verify the integrity of the information. Thus, public key electronic signatures provide authentication and data integrity. An electronic signature also provides non-repudiation, which means that it prevents the sender from claiming that he or she did not actually send the information. 6.10.4 WHY PUBLIC KEY INFRASTRUCTURE? How can you prove who you are over the Internet? In 'real life' you use some type of identification card (for example a driving license or a passport) to prove who you are. In the world of only ones and zeros, the digital certificate is your ID card. The ID cards in real life are distributed according to strict rules to avoid someone else getting hold of your ID card. The way of handling digital certificates is what PKI is all about. PKI is a way to solve the problem of the management of keys. In a large system, with thousands of users, there must be some automatic way of managing keys for encryption and authentication. With key management, we usually mean: generation of keys and digital certificates distribution of keys and digital certificates storage of keys and digital certificates validation of keys and di