Cryptography applies to different technologies, some examples of cryptography include:
Digital certificates
Authentication
PKI
RSA
PGP

Basic Terminology
Plain/Clear Text – Original text that was not yet altered.
Cipher Test – Opposite of plain text. This is scrambled message that you see after algorithm applied to it. It can also be reversed using algorithm and a key.
Algorithms – formula that describes how encryption description process performed at any given instance
Keys – discrete piece of information that determines the result or output of a given cryptographic operation.

Lets look at major types of cryptography: symmetric and asymmetric(public-key)

 

Symmetric Cryptography

Symmetric Cryptography
pros
Preserving confidentiality
Increased speed
Simplicity
Authenticity
cons
Key management
Lack of nonrepudiation features

All algorithms use same singe key for both encryption and decryption.

Examples of Symmetric Agorithms
DES-Data Encryption Standard
3DES Triple DES
RC2,4,5,6
AES
IDEA
Blowfish

 

Asymmetric – Public Key Cryptography

Uses key pair which includes public and private key. User given two keys public and private. Public key is published and private key remains private.
Both keys can be used to encrypt. When one key is used only the other one can reverse it.

Public key must be associated with user in a trusted manner. This is where PKI comes in.

Example of communication:
Public key
1. A wants to send message to B.
2. A locates B public key and use it to encrypt message.
3. When B receives message he will use his private key to decrypt this message.

Private key
1. A send message to B using private key.
2. B retrieves A public key to verify that correct private key was used.

Hash function is used to create and verify digital signature. It is one way process used to verify integrity of information. Hash function generates fixed length value that stays the same.
To perform verification of the message, hashing is used as part of digital signature creation.

Certificate authorities

Certificate authority confirms that key belongs to certain individual. CA issues digital certificate that is unique to individual , computer or service. The certificate issued under certain conditions and when they are vacillated CA will remove the certificate. For attacker to compromise the system they would need to hack private key of the server or private key of the issuer. CA creates and revokes certificates as well as public keys. CA can be Local or Public