Cryptography Explained: Secure Communication & Encryption Techniques

Cryptography is the study of secure communications techniques that allow only the sender and intended recipient of a message to view its contents. Specifically, these techniques are used to protect information that is obtained from mathematical concepts and a set of rule-based calculations or algorithms to convert messages, making them difficult to decode.

Originating back to Ancient Egypt, cryptography was believed to be used by Ancient Egyptians in complex hieroglyphics. Roman Emperor Julius Caesar has been credited with using one of the first modern ciphers.

Cryptography can be split into two eras--the classical era and the modern era. The turning point occurred in 1977 with the RSA algorithm and the Diffie-Hellman key exchange algorithm. More on that later.

Types of Cryptography

Traditionally, there are three types of cryptography: symmetric key, hash functions, and asymmetric key.

Symmetric Key

This is an encryption system where the sender and receiver of a message uses a single common key to encrypt and decrypt messages. While this method is faster and simpler than the other two methods, it is up to the sender and receiver to exchange the key in a secure manner.

The most popular example of this is Data Encryption System (DES). Let’s try the following example:

You have a message, “M”, you want to sent to your friend. You encrypt the message with a Key and get a cipher text, “C”.

Your friend gets the cipher text, C, to which she then decrypts the cipher text using the same Key to retrieve M.

There are two types of symmetric cryptography: stream ciphers and block ciphers.

Stream Ciphers

A stream cipher uses a fixed key that replaces the message with a pseudorandom string of characters. It encrypts each letter, one at a time.

For more information on steam ciphers, please click here.

Block Ciphers

These are a form of symmetric cryptography which uses a key of a fixed length to encrypt a block of fixed length.

For more information on block ciphers, please click here.

Hash Functions

In a Hash Function system, there is no key. Instead, a hash value with a fixed length is calculated based on the text, making it impossible for the contents of plain text to be recovered. Many operating systems use hash functions to encrypt passwords.

Asymmetric Key (Public Key)

Under this cryptography system, a pair of keys is used to encrypt and decrypt information. The public key is used for encryption and a private key for decryption. Even if the public key is known by everyone, the intended receiver can only decode it because they alone know the private key.