Cryptography

Cryptography & Information Security

When we talk about information security, cryptography acts main role. There won’t be any information security without cryptography. They both bond to each other unbreakable. Let’s get in to the topic lets discuss how cryptography works.

What is Cryptography? 

Sometimes you may never heard of cryptography. But sure, you may have heard about encrypting and decryption. Well these are the key features of cryptography. Cryptography is a mechanism which converting ordinary plain text into an unreadable form of text and vice-versa. Basic task in cryptography is to enable users to communicate securely over an insecure channel in a way that guarantees their transmission's privacy.

How Cryptography Works? 

To get cryptography into work we need a cryptographic algorithm. Cryptographic algorithm is simply a mathematical function (but it is not a simple function) that converts a plain text into a cipher text and vice-versa. This conversion from plain text to cipher text is called encryption, and reverse process is called decryption.

Example of encrypting a word

Plain text : cat

Cipher text : 13111201

Now how to convert this cipher text into the plain text again? To do this you need to find the key that I used to encrypt this text.

            

            Key: I have used 1 to separate letters, and letter positions in the alphabet to represent the                      letter.

           

            Now you know the key to decrypt the cipher text, you can now read the message.

Let’s come to the real world. Generally, we use two different methods for do this cryptography process.

1.Secret Key Cryptography (Symmetric Key Cryptography) (Private Key Cryptography)

In here we use a same key to encrypt and decrypt the message.

After sending an encrypted message to another end. The sender must send its private key to the other end unless receiver cannot decrypt the message. There occurs a key distributing problem. That if we send the key in the same channel where the message is sent. Then a hacker or an exploiter can get our both message and the key. Therefore, our message is vulnerable. This is the biggest problem in secret key cryptography. To overcome this issue, we must use a trusted third party to distribute the key or we can pre-shared the key and keep it secret between two parties. Verisign is a popular key distributing service. When data is not going anywhere this method is very efficient. However, this is quite expensive when transmitting data due the key distribute problem. This problem is solved in the public key cryptography. AES (advance encryption standard), DES (data encryption standard) are popular algorithms for secret key cryptography.

2.Public Key Cryptography (Asymmetric Key Cryptography)

The main problem in symmetric key cryptography was solved by public key cryptography. This method was introduced by Whitfield Diffie and Martin Hellman in 1975. This is also known as asymmetric key cryptography for the reason of using two keys to do the cryptographic process. OK let’s discuss how this works. There are two keys, one is public key, and another one is private key. You publish your public key to the world while keeping your private key secret. Now anyone with your public key can encrypt and send a message that can only be decrypted by using your private key. And in the same way when you have someone’s public key you can encrypt a message that can only be decrypted by his/her private key. By this way we don’t need to send our keys anywhere. We don’t get the key distribution problem here. RSA (Ron Rivest, Adi Shamir, and Leonard Adleman name for its inventors), Elgamal (named for its inventor, Taher Elgamal), Diffie-Hellman (named for its inventors) are some famous public key cryptographic algorithms all are named behalf of their inventors.