Introduction To Cryptography
Cryptography
Cryptography is the science of providing security for information. It has been used historically as a means of providing secure communication between individuals, government agencies, and military forces. Today, cryptography is a cornerstone of the modern security technologies used to protect information and resources on both open and closed networks.
According to Webopedia.com, Cryptography is defined as
The art of protecting information by transforming it (encrypting it) into an unreadable format, called cipher text. Only those who possess a secret key can decipher (or decrypt) the message into plain text. Encrypted messages can sometimes be broken by cryptanalysis, also called codebreaking, although modern cryptography techniques are virtually unbreakable.
Encryption
Encryption is the conversion of plain text into cipher text, which cannot be easily understood by anyone except authorized parties.
Decryption
It is the reverse of encryption. Decryption is the conversion of cipher text to plain text.
Types of Encryption
- Symmetric Cryptography
- Asymmetric Cryptography (Public Key)
Symmetric Cryptography
Symmetric-key algorithms are algorithms for cryptography that use the same cryptographic keys for both encryption of plaintext and decryption of ciphertext. The keys may be identical or there may be a simple transformation to go between the two keys. The keys, in practice, represent a shared secret between two or more parties that can be used to maintain a private information link. This requirement that both parties have access to the secret key is one of the main drawbacks of symmetric key encryption
Key(A) is a shared secret sequence of characters shared between to parties. The same key can be used for encryption and decryption
Asymmetric Cryptography (Public-key cryptography)
Asymmetric cryptography, is any cryptographic system that uses pairs of keys (public and private keys). The Public Key is used only for encryption and Private Key is used only for decryption.
In a public-key encryption system, any person can encrypt a message using the public key of the receiver, but such a message can be decrypted only with the receiver’s private key. For this to work it must be computationally easy for a user to generate a public and private key-pair to be used for encryption and decryption. The strength of a public-key cryptography system relies on the degree of difficulty (computational impracticality) for a properly generated private key to be determined from its corresponding public key. Security then depends only on keeping the private key private, and the public key may be published without compromising security. source
Cryptographic Hash
A cryptographic hash function is a hash function which takes an input (or ‘message’) and returns a fixed-size alphanumeric string, which is called the hash value (sometimes called a message digest, a digital fingerprint, a digest or a checksum).
The ideal hash function has three main properties:
- It is extremely easy to calculate a hash for any given data.
- It is extremely computationally difficult to calculate an alphanumeric text that has a given hash.
- It is extremely unlikely that two slightly different messages will have the same hash.
Functions with these properties are used as hash functions for a variety of purposes, not only in cryptography. Practical applications include message integrity checks, digital signatures, authentication, and various information security applications.
A hash function takes a string of any length as input and produces a fixed length string which acts as a kind of “signature” for the data provided. In this way, a person knowing the “hash value” is unable to know the original message, but only the person who knows the original message can prove the “hash value” is created from that message.
