Symmetric Key Cryptography | Cryptography Techniques

Cryptography in Network Security-

 

In network security,

• Cryptography is a method of storing and transmitting data in a particular form.
• It ensures that only the person for whom the message is intended can read the message.

 

The message exchange using cryptography involves the following steps-

 

 

Step-01:

 

At sender side,

• Using an encryption algorithm, the message is converted into an unreadable form.
• The message in unreadable form is called as cipher text.

 

Step-02:

 

• The cipher text is sent to the receiver over the communication channel.
• Since the message is encrypted, the attackers can not read the message.

 

Step-03:

 

At receiver side,

• Using a decryption algorithm, the message is again converted into the readable form.
• Then, receiver can read the message.

 

Cryptography Techniques-

 

Cryptography techniques may be classified as-

 

 

1. Symmetric Key Cryptography
2. Asymmetric Key Cryptography

 

In this article, we will discuss about symmetric key cryptography.

 

Symmetric Key Cryptography-

 

In this technique,

• Both sender and receiver uses a common key to encrypt and decrypt the message.
• This secret key is known only to the sender and to the receiver.
• It is also called as secret key cryptography.

 

Working-

 

The message exchange using symmetric key cryptography involves the following steps-

 

 

 

• Before starting the communication, sender and receiver shares the secret key.
• This secret key is shared through some external means.
• At sender side, sender encrypts the message using his copy of the key.
• The cipher text is then sent to the receiver over the communication channel.
• At receiver side, receiver decrypts the cipher text using his copy of the key.
• After decryption, the message converts back into readable format.

 

Symmetric Encryption Algorithms-

 

Some of the encryption algorithms that use symmetric key are-

• Advanced Encryption Standard (AES)
• Data Encryption Standard (DES)

 

Advantages-

 

The advantages of symmetric key algorithms are-

• They are efficient.
• They take less time to encrypt and decrypt the message.

 

Disadvantages-

 

Point-01:

 

The number of keys required is very large.

 

In symmetric key cryptography,

• Each pair of users require a unique secret key.
• If N people in the world wants to use this technique, then there needs to be N(N-1) / 2 secret keys.
• For 1 million people to communicate, a half billion secret keys would be needed.

 

How N(N-1)/2 Keys Will Be Required?   Consider a complete graph with N nodes. Consider each node represents one person. Then, each person will require (N-1) keys to communicate with other (N-1) people. Thus, each edge must have a unique key for communication. Thus, Number of keys required = Number of edges = nC2 = n(n-1)/2.

 

Point-02:

 

• Sharing the secret key between the sender and receiver is an important issue.
• While sharing the key, attackers might intrude.

 

To overcome this disadvantage, Diffie Hellman Key Exchange Algorithm is used for exchanging the secret key.

 

Important Points-

 

Point-01:

 

In symmetric key cryptography,

• Both sender and receiver uses the same key.
• Sender encrypts the message using his copy of the key.
• Receiver decrypts the message using his copy of the key.
• The key must not be known to anyone else other than sender and receiver.
• If the secret key is known to any intruder, he could decrypt the message.

 

Point-02:

 

• This cryptography technique is called as symmetric key cryptography.
• It is because both sender and receiver use the same key on their sides.

 

Point-03:

 

• This cryptography technique is called as secret key cryptography.
• It is because the key has to be kept secret between the sender and receiver.

 

To gain better understanding about Symmetric Key Cryptography,

Watch this Video Lecture

 

Next Article- Asymmetric Key Cryptography | RSA Algorithm

 

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