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Encryption is the method by which information is converted into secret code that hides the information's true meaning. The science of encrypting and decrypting information is called cryptography.

In computing, unencrypted data is also known asplaintext, and encrypted data is called ciphertext. The formulas used to encode and decode messages are called encryption algorithms or ciphers.

To be effective, a cipher includes a variable as part of the algorithm. The variable, which is called a key, is what makes a cipher's output unique. When an encrypted message is intercepted by an unauthorized entity, the intruder has to guess which cipher the sender used to encrypt the message, as well as what keys were used as variables. The time it takes to guess this information is what makes encryption such a valuable security tool.

At the beginning of the encryption process, the sender must decide what cipher will best disguise the meaning of the message and what variable to use as a key to make the encoded message unique. The most widely used types of ciphers fall into two categories: symmetric and asymmetric.

Symmetric ciphers, also referred to as secret key encryption, use a single key. The key is sometimes referred to as a shared secret because the sender or computing system doing the encryption must share the secret key with all entities authorized to decrypt the message. Symmetric key encryption is usually much faster than asymmetric encryption. The most widely used symmetric key cipher is the Advanced Encryption Standard (AES), which was designed to protect government-classified information.

Asymmetric ciphers, also known as public key encryption, use two different -- but logically linked -- keys. This type of cryptography often uses prime numbers to create keys since it is computationally difficult to factor large prime numbers and reverse-engineer the encryption. The Rivest-Shamir-Adleman (RSA) encryption algorithm is currently the most widely used public key algorithm. With RSA, the public or the private key can be used to encrypt a message; whichever key is not used for encryption becomes the decryption key.

Today, many cryptographic processes use a symmetric algorithm to encrypt data and an asymmetric algorithm to securely exchange the secret key.

Encryption plays an important role in securing many different types of information technology (IT) assets. It provides the following:

Encryption is commonly used to protect data in transit and data at rest. Every time someone uses an ATM or buys something online with a smartphone, encryption is used to protect the information being relayed. Businesses are increasingly relying on encryption to protect applications and sensitive information from reputational damage when there is a data breach.

There are three major components to any encryption system: the data, the encryption engine and the key management. In laptop encryption, all three components are running or stored in the same place: on the laptop.

In application architectures, however, the three components usually run or are stored in separate places to reduce the chance that compromise of any single component could result in compromise of the entire system.

The primary purpose of encryption is to protect the confidentiality of digital data stored on computer systems or transmitted over the internet or any other computer network.

This video from the Khan Academy explains how256-bit encryption works.

In addition to security, the adoption of encryption is often driven by the need to meet compliance regulations. A number of organizations and standards bodies either recommend or require sensitive data to be encrypted in order to prevent unauthorized third parties or threat actors from accessing the data. For example, the Payment Card Industry Data Security Standard (PCI DSS) requires merchants to encrypt customers' payment card data when it is both stored at rest and transmitted across public networks.

Hash functions provide another type of encryption. Hashing is the transformation of a string of characters into a fixed-length value or key that represents the original string. When data is protected by a cryptographic hash function, even the slightest change to the message can be detected because it will make a big change to the resulting hash.

Hash functions are considered to be a type of one-way encryption because keys are not shared and the information required to reverse the encryption does not exist in the output. To be effective, a hash function should be computationally efficient (easy to calculate), deterministic (reliably produces the same result), preimage-resistant (output does not reveal anything about input) and collision-resistant (extremely unlikely that two instances will produce the same result).

Popular hashing algorithms include the Secure Hashing Algorithm (SHA-2 and SHA-3) and Message Digest Algorithm 5 (MD5).

Encryption, which encodes and disguises the message's content, is performed by the message sender. Decryption, which is the process of decoding an obscured message, is carried out by the message receiver.

The security provided by encryption is directly tied to the type of cipher used to encrypt the data -- the strength of the decryption keys required to return ciphertext to plaintext. In the United States, cryptographic algorithms approved by the Federal Information Processing Standards (FIPS) or National Institute of Standards and Technology (NIST) should be used whenever cryptographic services are required.

Encryption is an effective way to secure data, but the cryptographic keys must be carefully managed to ensure data remains protected, yet accessible when needed. Access to encryption keys should be monitored and limited to those individuals who absolutely need to use them.

Strategies for managing encryption keys throughout their lifecycle and protecting them from theft, loss or misuse should begin with an audit to establish a benchmark for how the organization configures, controls, monitors and manages access to its keys.

Key management software can help centralize key management, as well as protect keys from unauthorized access, substitution or modification.

Key wrapping is a type of security feature found in some key management software suites that essentially encrypts an organization's encryption keys, either individually or in bulk. The process of decrypting keys that have been wrapped is called unwrapping. Key wrapping and unwrapping activities are usually carried out with symmetric encryption.

While encryption is designed to keep unauthorized entities from being able to understand the data they have acquired, in some situations, encryption can keep the data's owner from being able to access the data as well.

Key management is one of the biggest challenges of building an enterprise encryption strategy because the keys to decrypt the cipher text have to be living somewhere in the environment, and attackers often have a pretty good idea of where to look.

There are plenty of best practices for encryption key management. It's just that key management adds extra layers of complexity to the backup and restoration process. If a major disaster should strike, the process of retrieving the keys and adding them to a new backup server could increase the time that it takes to get started with the recovery operation.

Having a key management system in place isn't enough. Administrators must come up with a comprehensive plan for protecting the key management system. Typically, this means backing it up separately from everything else and storing those backups in a way that makes it easy to retrieve the keys in the event of a large-scale disaster.

For any cipher, the most basic method of attack is brute force -- trying each key until the right one is found. The length of the key determines the number of possible keys, hence the feasibility of this type of attack. Encryption strength is directly tied to key size, but as the key size increases, so too do the resources required to perform the computation.

Alternative methods of breaking encryptions include side-channel attacks, which don't attack the actual cipher but the physical side effects of its implementation. An error in system design or execution can enable such attacks to succeed.

Attackers may also attempt to break a targeted cipher through cryptanalysis, the process of attempting to find a weakness in the cipher that can be exploited with a complexity less than a brute-force attack. The challenge of successfully attacking a cipher is easier if the cipher itself is already flawed. For example, there have been suspicions that interference from the National Security Agency (NSA) weakened the DES algorithm, and following revelations from former NSA analyst and contractor Edward Snowden, many believe the NSA has attempted to subvert other cryptography standards and weaken encryption products.

Governments and law enforcement officials around the world, particularly in the Five Eyes (FVEY) intelligence alliance, continue to push for encryption backdoors, which they claim are necessary in the interests of national safety and security as criminals and terrorists increasingly communicate via encrypted online services.

According to the FVEY governments, the widening gap between the ability of law enforcement to lawfully access data and their ability to acquire and use the content of that data is "a pressing international concern" that requires "urgent, sustained attention and informed discussion."

Opponents of encryption backdoors have said repeatedly that government-mandated weaknesses in encryption systems put the privacy and security of everyone at risk because the same backdoors can be exploited by hackers.

Recently, law enforcement agencies, such as the Federal Bureau of Investigation (FBI), have criticized technology companies that offer E2EE, arguing that such encryption prevents law enforcement from accessing data and communications even with a warrant. The FBI has referred to this issue as "going dark," while the U.S. Department of Justice (DOJ) has proclaimed the need for "responsible encryption" that can be unlocked by technology companies under a court order.

Australia passed legislation that made it mandatory for visitors to provide passwords for all digital devices when crossing the border into Australia. The penalty for noncompliance is five years in jail.

By 2019, cybersecurity threats increasingly included encryption data on IoT and on mobile computing devices. While devices on IoT often are not targets themselves, they serve as attractive conduits for the distribution of malware. According to experts, attacks on IoT devices using malware modifications tripled in the first half of 2018 compared to the entirety of 2017.

Meanwhile, NIST has encouraged the creation of cryptographic algorithms suitable for use in constrained environments, including mobile devices. In a first round of judging in April 2019, NIST chose 56 lightweight cryptographic algorithms candidates to be considered for standardization. Further discussion on cryptographic standards for mobile devices is slated to be held in November 2019.

In February 2018, researchers at MIT unveiled a new chip, hardwired to perform public key encryption, which consumes only 1/400 as much power as software execution of the same protocols would. It also uses about 1/10 as much memory and executes 500 times faster.

Because public key encryption protocols in computer networks are executed by software, they require precious energy and memory space. This is a problem in IoT, where many different sensors embedded in products such as appliances and vehicles connect to online servers. The solid-state circuitry greatly alleviates that energy and memory consumption.

The word encryption comes from the Greek word kryptos, meaning hidden or secret. The use of encryption is nearly as old as the art of communication itself. As early as 1900 B.C., an Egyptian scribe used nonstandard hieroglyphs to hide the meaning of an inscription. In a time when most people couldn't read, simply writing a message was often enough, but encryption schemes soon developed to convert messages into unreadable groups of figures to protect the message's secrecy while it was carried from one place to another. The contents of a message were reordered (transposition) or replaced (substitution) with other characters, symbols, numbers or pictures in order to conceal its meaning.

In 700 B.C., the Spartans wrote sensitive messages on strips of leather wrapped around sticks. When the tape was unwound, the characters became meaningless, but with a stick of exactly the same diameter, the recipient could recreate (decipher) the message. Later, the Romans used what's known as the Caesar Shift Cipher, a monoalphabetic cipher in which each letter is shifted by an agreed number. So, for example, if the agreed number is three, then the message, "Be at the gates at six" would become "eh dw wkh jdwhv dw vla." At first glance, this may look difficult to decipher, but juxtaposing the start of the alphabet until the letters make sense doesn't take long. Also, the vowels and other commonly used letters, like t and s, can be quickly deduced using frequency analysis, and that information, in turn, can be used to decipher the rest of the message.

The Middle Ages saw the emergence of polyalphabetic substitution, which uses multiple substitution alphabets to limit the use of frequency analysis to crack a cipher. This method of encrypting messages remained popular despite many implementations that failed to adequately conceal when the substitution changed -- also known as key progression. Possibly the most famous implementation of a polyalphabetic substitution cipher is the Enigma electromechanical rotor cipher machine used by the Germans during World War II.

It was not until the mid-1970s that encryption took a major leap forward. Until this point, all encryption schemes used the same secret for encrypting and decrypting a message: a symmetric key.

Encryption was almost exclusively used only by governments and large enterprises until the late 1970s when the Diffie-Hellman key exchange and RSA algorithms were first published and the first PCs were introduced.

In 1976, Whitfield Diffie and Martin Hellman's paper, "New Directions in Cryptography," solved one of the fundamental problems of cryptography: how to securely distribute the encryption key to those who need it. This breakthrough was followed shortly afterward by RSA, an implementation of public key cryptography using asymmetric algorithms, which ushered in a new era of encryption. By the mid-1990s, both public key and private key encryption were being routinely deployed in web browsers and servers to protect sensitive data.

Read more:
What is Encryption? - Definition from WhatIs.com