What Is Cryptography? Definition & How It Works

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Modern cryptography is a method of sending and receiving messages that only the intended receiver and sender can read — to prevent third-party access. It often involves encryption of electronic data, which commonly creates ciphertext by scrambling regular text. Then, it uses a decryption key of some form to return it to readable format on the receiving end. Cryptography can involve either a symmetric key system, which is the simplest, or an asymmetric key system, which is typically more secure. Cryptography provides methods for secure communication and electronic data that malicious adversaries cannot read, interpret, or access.

What is cryptography?

Cryptography is used to keep messages and data secure from being accessible to anyone other than the sender and the intended recipient. It is the study of communications and a form of security for messaging. Ultimately, cryptography can keep data from being altered or stolen. It can also be used to authenticate users. Cryptography often uses encryption and an algorithm to keep electronic data and messages secure and only readable by the intended parties. Cryptography has been around for centuries. The term itself comes from the Greek word kryptos, which translates to hidden. Today, cryptography is based on computer science practices and mathematical theory.

Types of cryptography

There are two main types of cryptography used for digital data and secure messages today: symmetric cryptography and asymmetric cryptography. Hash functions, a third type, doesn’t involve use of a key.

  • Symmetric cryptography: This is one of the most commonly used and simplest forms of encrypting and decrypting electronic data. It is also called secret-key or private-key cryptography. With symmetric cryptography, both the sender and the recipient will have the same key. This key is used to encrypt messages and data on one end and then decrypt it on the other end. Before communications begin, both parties must have the same secret key. Symmetric cryptography is fast, easy to use, and best suited for transmitting large amounts of data or for bulk encryption. The issue with this form of cryptography is that if a third party gets the secret key, they too can read and decrypt the data or messages. There are two main forms of symmetric encryption algorithms: stream and block algorithms.
    • Stream algorithm: This type encrypts the data while it is being streamed; therefore, it is not stored in the system’s memory. One of the most popular stream cyphers is the RC4 (Rivest Cipher 4), which encrypts messages one byte at a time.  
    • Block algorithms: This type encrypts specific lengths of bits in blocks of data using the secret key. The data is held within the system’s memory while blocks are completed. The Advanced Encryption Standard (AES) is the most commonly used symmetric algorithm. Blocks of 128-bit data are encrypted and decrypted using cryptographic keys of 128, 192, and 256 bits. The AES is FIPS (Federal Information Processing Standards) approved under guidance from NIST (National Institute of Standards and Technology).  
  • Asymmetric cryptography: This is also called public-key cryptography, and it involves the use of two different keys. A public key is distributed widely to everyone to encrypt data. This key is required to send messages and encrypt them. A sender can request the public key for the recipient to encrypt the data. Then, it will require the private key, which is kept secret, to decrypt the message. The key pair of the private and public key are mathematically related. Both keys are needed to perform operations, send and receive encrypted data and messages, and access sensitive data. Asymmetric cryptography needs higher processing and longer keys, with pieces of data that are smaller than the key; therefore, is often used on a smaller scale. Asymmetric and symmetric cryptography can be used together in a cryptosystem. Asy