Cryptography

Cryptography is the study and practice of techniques for secure communication, allowing only the sender and intended recipient of a message to view its contents. Cryptography is closely related to encryption, the process of scrambling readable text such that it can only be read by people with a secret code, or decryption key. Cryptography also covers hiding information in images through techniques such as microdots or merging.

The term, cryptography, is derived from the Greek word kryptos (meaning hidden), and its practice dates back through history. The ancient Egyptians were known to use cryptographic methods in complex hieroglyphics and Julius Caesar is credited as using one of the first modern ciphers. The "Caesar cipher" uses a simple substitution technique to encrypt information by shifting letters a fixed number of positions through the alphabet.

Modern cryptography has become vital for computer and communications security. It is based on a range of mathematical concepts including number theory, computational complexity theory, and probability theory.

There are five primary functions of cryptography:

1. Privacy/confidentiality—ensuring only the intended receiver can read messages sent
2. Authentication—proving one's identity
3. Integrity—the assurance that the message has not been altered from the original
4. Non-repudiation—proving the sender is the one sending the message
5. Key exchange—sharing of crypto keys are shared between sender and receiver.

There are several ways of dividing modern cryptographic algorithms including the number of keys required and the intended use. The following are three common types of cryptographic algorithms:

• Symmetric encryption—uses a single key for both encryption and decryption
• Asymmetric encryption—uses separate keys for encryption and decryption
• Hash Functions—uses a mathematical transformation to irreversibly encrypt information providing a digital fingerprint

Cryptanalysis is a closely related field to cryptography, concerned with the decryption and analysis of codes, ciphers, or encrypted text. Cryptanalysis uses mathematical formulas to find algorithm vulnerabilities to break cryptography or information security systems. Examples of cryptanalysis attacks include the following:

• Known-Plaintext Analysis
• Chosen-Plaintext Analysis
• Ciphertext-Only Analysis
• Man-in-the-Middle Attack

Modern cryptography has a range of applications, such as providing secure communication and data protection across a range of fields including eCommerce and the military.

Blockchains and cryptocurrencies are made possible through asymmetric cryptography. Each transaction is recorded to the blockchain ledger using encrypted data, with users accessing their information and making transactions using a public and private key. Blockchains also use hash functions to securely record and store transactions. Through cryptographic hashing, newly verified transactions can be irreversibly added to a blockchain.