SECURING FIBRE CHANNEL FABRICS - Brocade

Chapter 5: Elementary CryptographySymmetric vs. Asymmetric CryptographyOne of the enduring problems in cryptography is the distribution ofkeys. How do you distribute a secret key and minimize or eliminate therisk of the key being compromised if it is intercepted? This problem iscompounded when the key used to encrypt the message is the sameas the one used to decrypt it. Before the electronic era, the only way toexchange keys was to meet in person or deliver them the old-fashionedway, and exchange the keys verbally or via printed copy.Symmetric KeysSymmetric cryptography uses the same key or a secret key to encryptand decrypt messages, such as the Cesar cipher. Since the same keyis used for both encryption and decryption, anyone in possession ofthe key can decrypt the message encoded using that key. Distributingthe keys to the authorized persons poses a particular challenge andextreme measures sometimes need to be taken for what is termed asecure key exchange. If the key is stolen or intercepted during thetransfer process, the code is broken and the encrypted message nolonger deemed secure. Examples of well-known symmetric key algorithmsare Data Encryption Standard (DES) 3DES (pronounced “tripleDEZ”), and Advanced Encryption Standard (AES).Asymmetric KeysAsymmetric cryptography has been developed to address the keyexchange problem. Exchanging keys in times of war on the battlefieldcertainly posed a challenge, but the Internet and e-commerce presenteven greater challenges. How can you conduct millions of transactionsper day at wire speeds across the world and make sure you authenticateeach transaction?Asymmetric cryptography is also referred to as public key cryptography,since it makes use of keys that are known publicly. A public keyexchange system works on the principle of encrypting a messageusing a combination of a known public key and a secret private key.Each party has their own public and private key pairs, which are differentbut mathematically related. Examples of familiar asymmetric keyalgorithms are used with Public Key Infrastructure (PKI) and RSA (representsthe family names of the inventors: Rivest, Shamir, andAdelman).There are several ways of implementing public key exchanges. Below isa high-level example of how this works, without going into too manydetails of how it is actually accomplished.76 Securing Fibre Channel Fabrics