Cryptography

Cryptography is the art and science of encrypting and decrypting data for the purpose of secrecy or authenticity. It facilitates the secure storage and transmission of critical data in an insecure network, Technically, cryptography is the process of using (or studying) electronic security systems, methods, or schemes that protect data by altering it in a way so that only the intended recipient is able to extract the original information. Encryption and Decryption mechanisms use an algorithm and a secret value that is known as a Key.

A cryptographic algorithm, alternatively referred to as a cipher, is used for data encryption and decryption. A cipher is a mathematical function. This algorithm works with a key, which may either be a word, a number or a phrase for encrypting plain text. Algorithms are openly available, whereas Keys are kept secret and are used for providing the required security. Keys, also known as crypto variables, are the information or a sequence that control the enciphering and deciphering of messages. The data security is dependent on the strength of the algorithm and the secrecy of the key.

All possible keys and protocols, together with the cryptography algorithm, form the cryptosystem. Conventional cryptography is also referred to as symmetric key encryption or secret key. It uses only one key for encrypting and decrypting the data. In asymmetric cryptography, the public key is used for encrypting while the private key is used for decrypting. The major benefit of this system is that it allows the secure transfer of data even among entities who don't have any permanent security arrangement.

A good example of a cryptosystem. is the Pretty Good Privacy (PGP). PGP combines both conventional and public key cryptography. It can be termed as a hybrid cryptosystem. While using PGP, the data first gets compressed, thus saving time and disk space. The most important benefit of such compression is the enhancing of cryptographic security. Compression makes it more difficult for attackers to decipher the text. The PGP then creates a secret key that is randomly generated and is used only once. The secret key in combination with the encryption algorithm encrypts; the plain text. After data encryption, the secret key is encrypted to recipients' public key. This, along with the cipher text, is sent to the recipient.

There are three types of cryptographic algorithms. These are described below:

Symmetric Key Cryptography: Also known as Private Key Cryptography or Single Key Cryptography, it uses the same key for encrypting and decrypting messages. In this case, since the key is the only data required to decrypt the cipher text, it is kept secret.

Public Key Cryptography: This algorithm uses a set of two complimentary keys for encryption and decryption. A public key is used to encrypt the message and a private key for decrypting the cipher text. Hence, a person having the public encryption key may encrypt and send a message to another person. However, only the person having the private decryption key can decipher the message. Both keys, referred to as a key pair, are created and used together.

Hybrid Public/Private Cryptography: In this case, a combination of public and private key cryptography is used. An exchange of an encrypted session key is done by using public key cryptography. The encrypted session that follows the exchanges is then pursued with private/symmetric key cryptography.

Objectives of Cryptography

The main objectives of cryptography are explained below:

Authentication: This is achieved through two main services provided by cipher systems. The first service involves the identification of the origin of a message and verification of its authenticity. The second service involves the verification of the identity of the person trying to access the information and determining if the person is authorized for the same.

Confidentiality: Confidentiality is about providing privacy for messages and data by hiding the information using various encryption techniques.

Integrity: Both the senders and the recipient need to be assured that message remains unaltered.

Non repudiation: It provides the proof that the document came from the sender even when the recipient tries to deny that.

The technology normally used for achieving the above mentioned objectives of cryptography is Public Key Infrastructure (PKI). PKI is an online infrastructure that uses digital signatures, digital certificates and secure channels to secure applications, communications and transactions. In the following section, we will examine PKI, its benefits and various PKI products. We will also analyze the instruments used for enabling security.

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