SECURING FIBRE CHANNEL FABRICS - Brocade

Cryptographic AlgorithmsHashing algorithms are often used for error-checking, but in IT security,they are generally used to verify the integrity of a message. For example,hackers may sometimes modify code, particularly freeware, and add aback door, virus, or some other type of malware into the code. When theoriginal software package is passed through a hashing algorithm, ahash value is generated, which can then be posted in a public location.If someone downloads this software package and puts it through thesame hashing algorithm, the resulting hash value should match the oneposted. If they do not match, then it can be assumed that the softwarehas been modified and cannot be trusted to be secure.An MD by itself only provides integrity verification, but an MD can beencrypted with a symmetric key to provide authentication of the provenanceof the data. This technique is known as a messageauthentication code (MAC).Digital SignaturesA digital signature, shown in Figure 31, is exactly what it says: it is theequivalent of a person's paper signature but for digital transactions.Digital signatures cannot be repudiated later, that is, it would not bepossible to deny that someone or something actually sent a messageor made a transaction.A digital signature is created as follows:1. A message is created.2. The message is passed through an algorithm to generate a hashvalue.3. The hash value is encrypted using a private key from some public/private key authority.4. The resulting encrypted hash is the digital signature.The validation process at the other end goes as follows:1. The message is passed through the same hashing algorithm.2. The digital signature is decrypted using the public key of thesender.3. The resulting decrypted hash is compared with the newly calculatedhash.4. If the hash values match then the message is deemed valid.Securing Fibre Channel Fabrics 81