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# Cryptography Techniques

[Rice University]

### - Overview

Barely a week goes by without reports of some new mega-hack that’s exposed huge amounts of sensitive information, from people’s credit card details and health records to companies’ valuable intellectual property.

The threat posed by cyberattacks is forcing governments, militaries, and businesses to explore more secure ways of transmitting information.

Cryptography can ensure the confidentiality and integrity of both data in transit as well as data at rest. It can also authenticate senders and recipients to one another and protect against repudiation.

### - Purposes of Cryptography

Cryptography techniques are used to prevent unauthorized access to data. They have three basic purposes:
• Authentication: Verifying the identity of a user or computer
• Confidentiality: Keeping the contents of the data secret
• Integrity: Ensuring that data doesn't change between the time it leaves the source and the time it reaches its destination

Cryptography uses codes to protect information and communications so that only the intended audience can read and process it. Here are some cryptography techniques:
• Symmetric key cryptography: A single key that can be used for both encryption and decryption. The most popular type of symmetric key cryptography is Data Encryption System (DES).
• Asymmetric cryptography: Also known as public-key cryptography, this technique uses two different keys. One key is used for encryption and the other corresponding key is used for decryption.
• Quantum cryptography: Uses quantum mechanics principles to create unbreakable codes.
• Elliptic curve cryptography (ECC): A form of public-key cryptography that is based on the algebraic structure of elliptic curves over finite fields.
• Multivariate cryptography: Uses multiple variables to secure data. This technique is used in applications such as digital signatures, authentication, and payment systems.
• Block ciphers: A type of symmetric cryptography algorithm that encrypts data in fixed-sized blocks. They are commonly used to secure communications and data storage, and can be used to create digital signatures.
• One-way hash algorithms: A cryptographic hash algorithm produces a fixed-length output string (often called a digest) from a variable-length input string. The input serves as the plaintext, and the output hash is the cipher.
• Advanced Encryption Standard (AES): This cryptography standard encrypts blocks of text instead of encrypting each character individually.
• Cryptographic key management: This process creates, distributes, stores, and destroys encryption keys.
• Cryptographic primitives: These are well-established, low-level cryptographic algorithms that perform a single specific task.
• RSA: This is one of the most widely used public-key cryptographic systems. It's a block cipher where both the plaintext and ciphertext are integers in the range 0 to n−1.
• Key exchange algorithms: These cryptographic methods generate shared keys that are shared among users.

Some other cryptography techniques include: Simple codes, Steganography, Hashing.

Although hybrid systems do exist (such as the SSL internet protocols), most encryption techniques fall into one of three main categories: symmetric cryptography algorithms, asymmetric cryptography algorithms, or hash functions.

### - Some Examples of Cryptography

Here are some examples of cryptography:

• Public key cryptography: Also known as asymmetric cryptography, this form of cryptography uses two keys. One key is public and can be shared with anyone, while the other key is private and used for decryption. Public key cryptography is used by the Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols to encrypt data between a web server and a client.
• Digital signatures: A mathematical scheme that verifies the authenticity of digital messages or documents. A valid digital signature on a message gives the recipient confidence that the message came from a sender known to the recipient.
• Key exchange: A method in cryptography that allows two parties to exchange cryptographic keys. This allows the two parties to agree on a shared secret, which can then be used to encrypt communications.

Examples of public-key cryptography include:
• RSA, used widely on the internet.
• Elliptic Curve Digital Signature Algorithm (ECDSA) used by Bitcoin.
• Digital Signature Algorithm (DSA) adopted as a Federal Information Processing Standard for digital signatures by NIST in FIPS 186-4.
• Diffie-Hellman key exchange.

### - Quantum Key Distribution (QKD)

Today, sensitive data is often encrypted and then sent over fiber-optic cables and other channels along with the digital "keys" needed to decode the information. Data and keys are sent as classical bits—streams of electrical or optical pulses representing 1s and 0s. This makes them vulnerable. Clever hackers can read and copy bits in transit without leaving a trace.

Quantum communication uses the laws of quantum physics to protect data. These laws allow particles—typically photons that carry data along fiber optic cables—to assume a state of superposition, meaning they can represent multiple combinations of 1s and 0s at the same time. These particles are called quantum bits, or qubits.

From a cybersecurity perspective, the beauty of qubits is that their ultra-fragile quantum states can "collapse" to a 1 or 0 if a hacker tries to observe them in transit. This means hackers cannot tamper with the qubits without leaving them behind. A clear sign of activity.

Some companies have exploited this property to create networks to transmit highly sensitive data based on a process known as quantum key distribution, or QKD. These networks are super secure, at least in theory.

[More to come ...]