Chapter 11

This chapter dealt with the basics of cryptography. The first part of the chapter defined what cryptography was; essentially it is obscuring data in such a way as to make it unreadable and incomprehensible to those who are not authorized or meant to read it. Stenography is the practice of hiding a message or data amongst something in order to obscure it. The book described how cryptography was deciphered through a key that unlocks an algorithm that decrypts the data into plaintext. Cryptography protects the identity of the sender, the integrity of the data and the authenticity of the message. Hashing algorithms are fingerprints of the encrypted data. A message digest is another algorithm used and has 3 versions. MD2 takes plaintext and and creates a 128 bit hash from it. MD4 does the same thing as MD2, but adds enough padding to the message to go to 512 bits in length. MD5 is a revision of MD4 but uses 4 variables to create the hash. Secure Hash Algorithm (SHA) is another hashing algorithm and has a few versions, including SHA-0 and SHA-1. These versions create a hash 160 bits long. RIPEMD is a hash algorithm developed from MD4 and it uses 2 different and independent chains of computation which are combined at the end of the process to create the hash. Passwords are used to store passwords. Symmetric algorithms use the same key to both encrypt and decrypt a file. DES, 3DES, AES, Rivest, RC4 and Blowfish all use the symetric method in their function. Asymmetric cryptography, also known as PKI (public key encryption) uses a different key to encrypt than it does to decrypt a file. In PKI, there are 2 keys, a public key and a private key. The use of this system verifies the user in addition to decrypting the information contained in the message. PGP uses asymmetric cryptography, as does EFS (the system used on Microsoft software). BitLocker uses it as well, and is used to encrypt an entire hard disk. USB devices can be used to provide encryption as well. Lastly, a trusted platform module (TPM) can be used, and is a hardware chip on a motherboard that is a dedicated cryptographic device. Some computers use a hardware security module, which is a dedicated cryptographic processor to handle encryption on a computer.