SECURING FIBRE CHANNEL FABRICS - Brocade

Chapter 5: Elementary CryptographyCryptographic AlgorithmsA cryptographic algorithm or cipher is the actual procedure used tomanipulate a readable message and render it unreadable. The readablemessage that is input to a cipher is called plaintext and its outputis called ciphertext.Early thinking around ciphers encouraged security through obscurity.Proprietary algorithms were kept secret for fear of their being discoveredand subsequently broken. With certain exceptions, notablymilitary-grade applications, this thinking has been replaced by the useof open algorithms that withstand public scrutiny. August Kerckhoffproposed six rules for military cryptography in 1883 such that if anencryption algorithm were to fall into enemy hands, it would not resultin a compromise of the message as long as the key was not discovered.Proprietary encryption algorithms are generally not considered assecure, since they do not benefit from being scrutinized by either thecryptographic community at large or the general public. These algorithmsare usually analyzed by a group of elite professionalcryptographers, who sometimes have tunnel vision and see thingsfrom only one perspective, a situation which could result in a gapingflaw that is overlooked.An open algorithm, on the other hand, has this advantage: at somepoint thousands of individuals attempted to break it. If thousands ofpeople from different professions and viewpoints are unable to breakthe code, then the algorithm certainly can be considered more securethan without having been through such a rigorous process. Whensomeone eventually breaks the code, it will become public knowledgeand the algorithm will have ended its useful life.Designing a cryptographic algorithm is very complex and should takethe factors listed below into consideration, so it can be used efficientlyin practical commercial applications:• Speed of encryption. A highly complex and completely unbreakablealgorithm would have no practical commercial use if it alsorequired an inordinate amount of processing power to compute,which would drastically impact performance.• Memory usage. Algorithms that use too much memory to performtheir computations and manipulations may require memory componentstoo large to physically fit into certain portable devices,restricting their practical application.78 Securing Fibre Channel Fabrics