SECURING FIBRE CHANNEL FABRICS - Brocade

Chapter 5: Elementary CryptographyStream CiphersStream ciphers process plaintext one bit at a time, as shown inFigure 29. Generally, stream ciphers are considered less secure, sincethere is a higher risk of having repeating patterns. For this reason,block ciphers are more commonly used. Block ciphers can, however,be used on streaming data when they are operating in a streamingmode of operation, such as the counter (CTR) mode discussed later inthis chapter.9 8 7 6 5 4 3Plaintext data bit streamKeyIndividual bits areencrypted one at a timeStreamcipher3’2’1’Ciphertext databit streamStreamCipherEncryptionProcess9’ 8’ 7’ 6’ 5’ 4’ 3’Ciphertext data bit streamKeyIndividual bits aredecrypted one at a timeStreamcipher321Plaintext databit streamStreamCipherDecryptionProcessFigure 3. Stream cipher encryption/decryptionBoth the block and stream ciphers address the data confidentialityissue by rendering the data unreadable without the key. Hashing algorithms,on the other hand, address the integrity issue by providing ameans to verify that data has not been modified.Hashing AlgorithmsHashing algorithms, shown in Table 30, are used to convert a messageof variable length to a shorter, sometimes fixed, length or numericalvalue. The resulting value is sometimes called a message digest (MD).These algorithms are also called one-way hashing functions since theyonly work in one direction, and it is not possible to reconstruct the originalmessage from the message digest. As a real-world example, abook could not be reconstructed in its entirety from a simple summaryof the book.PLAINTEXT MESSAGEHashalgorithmOne-way functionHash valueNot possible tocalculate originalmessage from thehash valuePLAINTEXT MESSAGEFigure 4. Hashing algorithm80 Securing Fibre Channel Fabrics