CRYPTOGRAPHY

1. Two types of encryption algorithms exist: two-way and one-way functions. Two-way functions are used to operate on plain text to encrypt it with the intention of later operating on that cipher text in some way to decipher or decrypt it.
2. Two-way functions include symmetric and asymmetric algorithms.
3. Symmetric cryptography works by providing both parties the same key for encryption and decryption. It provides confidentiality and is hard to break. Its weakness is that the keys are subject to exposure and must be transmitted through a channel other than the message.
4. Data Encryption Standard (DES) is a block encryption algorithm that is based on IBM's 128-bit algorithm; 56 bits make up the key and 8 bits are used for parity. DES can be implemented in one of four modes:

   Electronic Code Book (ECB) Native encryption mode that is used for small amounts of data. ECB is the weakest form of DES.

   Cipher Block Chaining (CBC) Works by taking each data from the previous and applying it to the next.

   Cipher Feedback Mode (CFB) Emulates a stream cipher and can be used when the encryption of individual characters is required.

   Output Feedback Mode (OFB) Also emulates a stream cipher and generates random binary bits that are combined with the plain text to create cipher text.

5. Asymmetric algorithms use two different keys. The advantage is that key distribution is easier. Asymmetric algorithms are not as fast as symmetric systems.
6. Asymmetric algorithms include Diffie-Hellman, El Gamal, and Elliptic Curve Cryptosystem algorithms.
7. Common hashing algorithms include MD2, MD4, MD5, HAVAL, and SHA-1.
8. A public key infrastructure (PKI) allows individuals using the Internet to obtain and share cryptographic keys from a trusted authority. The PKI consists of four basic components and is governed by the X.509 standards:

   Certificate Authority (CA) Used to verify and issue digital certificates. The certificate includes the public key and information about it.

   Registration Authority (RA) Verifies authenticity for the CA.

   Repository Accepts certificates and distributes them to authorized parties.

   Archive Responsible for the long-term storage of archived information distributed from the CA.