Types of CRYPTOGRAPHY ALGORITHMS

The cryptography algorithms can be classified into two types as:

• Symmetric key or secret key cryptography algorithms
• Public key or asymmetric cryptography algorithms.

Symmetric Key Cryptography

• It is also called as the secret key cryptography.

In the symmetrical key cryptography, the same key(shared secret key) is used by the sender and the receiver.

The same secret key is used at the sending end as well as at the receiving end .
The sender uses this key along with the encryption algorithm to encrypt the data, and receiver uses it along with the decryption algorithm to decrypt the data.

The encryption algorithm makes use of a combination of addition and multiplication to encrypt the data whereas the decryption algorithm uses a combination of subtraction and division in order to carry out the decryption.

The encryption and decryption algorithms are thus inverse of each other.
Thus, Encryption is equivalent to locking the message in a box while Decryption is equivalent to unlocking the box.

Advantages of Symmetric Key Ciphers:

1 The major advantages of symmetric key algorithm is that it is more efficient than the public key algorithms. It takes less time to encrypt a message using the symmetric key algorithm. This is because this key is of smaller size(length).
2 The symmetric key algorithms can be used for encryption and decryption of long messages.

Disadvantages of Symmetric Key Ciphers:

1 The first disadvantage is that the sender and receiver both should have a unique symmetric key. So large number of keys are required when the number of users increases.
2 The distribution of keys between two users can be difficult.

Public(Asymmetric) Key Cryptography

The public key cryptography is also called as asymmetric key cryptography .
In this type of cryptography, two keys are used by the system:
- Private Key
- Public Key

Out of them, the private key is kept by the receiver and it is not known to all whereas public key is announced to the public and everyone knows it.
Following diagram shows the schematic for public key cryptography

In this system, the sender uses the public key to encrypt the message to be sent. At the receiver, this message is decrypted with the help of receivers private key.

The public key used for encryption is different from the private key used for decryption. The public key is known to everyone but the private key is available only to an individual.

The private key for each end user will be different from all others. It is important to know that, even after the advent of asymmetric key cryptography, the need of symmetric key cryptography is still there.
This is because asymmetric key cryptosystem is much slower that the symmetric key cryptosystem. Therefore, the symmetric key cryptography is still needed for encryption of large messages.

Advantages of Asymmetric Key Cryptography:

1 There is no compulsion of using(sharing) the same key by the sender and receiver.
2 The number of keys required reduces drastically.

Disadvantages of Asymmetric Key Cryptography:

1 The algorithms used are highly complex.
2 It takes a long time to calculate ciphertext from plaintext. Therefore, it is very slow.
3 It is necessary to verify the association between a sender and this public key.