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What is encryption?

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 as plaintext, 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 and difficulty of guessing this information is what makes encryption such a valuable security tool.

Encryption has been a longstanding way for sensitive information to be protected.  Historically, it was used by militaries and governments.  In modern times, encryption is used to protect data stored on computers and storage devices, as well as data in transit over networks.  

Why is encryption important?

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

  • Confidentiality encodes the message's content.
  • Authentication verifies the origin of a message.
  • Integrity proves the contents of a message have not been changed since it was sent.
  • Nonrepudiation prevents senders from denying they sent the encrypted message.

How is encryption used?

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.

How does encryption work?

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 example
How algorithms and keys are used to make a plaintext message unintelligible

What are the benefits of encryption?

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.

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.

What are the disadvantages of 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.

Encryption key management and wrapping

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.

Types of encryption

  • Bring your own encryption (BYOE) is a cloud computing security model that enables cloud service customers to use their own encryption software and manage their own encryption keys. BYOE may also be referred to as bring your own key (BYOK). BYOE works by enabling customers to deploy a virtualized instance of their own encryption software alongside the business application they are hosting in the cloud.
  • Cloud storage encryption is a service offered by cloud storage providers whereby data or text is transformed using encryption algorithms and is then placed in cloud storage. Cloud encryption is almost identical to in-house encryption with one important difference: The cloud customer must take time to learn about the provider's policies and procedures for encryption and encryption key management in order to match encryption with the level of sensitivity of the data being stored.
  • Column-level encryption is an approach to database encryption in which the information in every cell in a particular column has the same password for access, reading and writing purposes.
  • Deniable encryption is a type of cryptography that enables an encrypted text to be decrypted in two or more ways, depending on which decryption key is used. Deniable encryption is sometimes used for misinformation purposes when the sender anticipates, or even encourages, interception of a communication.
  • Encryption as a Service (EaaS) is a subscription model that enables cloud service customers to take advantage of the security that encryption offers. This approach provides customers who lack the resources to manage encryption themselves with a way to address regulatory compliance concerns and protect data in a multi-tenant environment. Cloud encryption offerings typically include full-disk encryption (FDE), database encryption or file encryption.
  • End-to-end encryption (E2EE) guarantees data being sent between two parties cannot be viewed by an attacker that intercepts the communication channel. Use of an encrypted communication circuit, as provided by Transport Layer Security (TLS) between web client and web server software, is not always enough to ensure E2EE; typically, the actual content being transmitted is encrypted by client software before being passed to a web client and decrypted only by the recipient. Messaging apps that provide E2EE include Facebook's WhatsApp and Open Whisper Systems' Signal. Facebook Messenger users may also get E2EE messaging with the Secret Conversations option.
  • Field-level encryption is the ability to encrypt data in specific fields on a webpage. Examples of fields that can be encrypted are credit card numbers, Social Security numbers, bank account numbers, health-related information, wages and financial data. Once a field is chosen, all the data in that field will automatically be encrypted.
  • FDE is encryption at the hardware level. FDE works by automatically converting data on a hard drive into a form that cannot be understood by anyone who doesn't have the key to undo the conversion. Without the proper authentication key, even if the hard drive is removed and placed in another machine, the data remains inaccessible. FDE can be installed on a computing device at the time of manufacturing, or it can be added later on by installing a special software driver.
  • Homomorphic encryption is the conversion of data into ciphertext that can be analyzed and worked with as if it were still in its original form. This approach to encryption enables complex mathematical operations to be performed on encrypted data without compromising the encryption.
  • HTTPS enables website encryption by running HTTP over the TLS protocol. To enable a web server to encrypt all content that it sends, a public key certificate must be installed.
  • Link-level encryption encrypts data when it leaves the host, decrypts it at the next link, which may be a host or a relay point, and then reencrypts it before sending it to the next link. Each link may use a different key or even a different algorithm for data encryption, and the process is repeated until the data reaches the recipient.
  • Network-level encryption applies cryptoservices at the network transfer layer -- above the data link level but below the application level. Network encryption is implemented through Internet Protocol Security (IPsec), a set of open Internet Engineering Task Force (IETF) standards that, when used in conjunction, create a framework for private communication over IP networks.
  • Quantum cryptography depends on the quantum mechanical properties of particles to protect data. In particular, the Heisenberg uncertainty principle posits that the two identifying properties of a particle -- its location and its momentum -- cannot be measured without changing the values of those properties. As a result, quantum-encoded data cannot be copied because any attempt to access the encoded data will change the data. Likewise, any attempt to copy or access the data will cause a change in the data, thus notifying the authorized parties to the encryption that an attack has occurred.

Cryptographic hash functions

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 vs. decryption

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 algorithms

  • AES is a symmetric block cipher chosen by the U.S. government to protect classified information; it is implemented in software and hardware throughout the world to encrypt sensitive data. NIST started development of AES in 1997 when it announced the need for a successor algorithm for the Data Encryption Standard (DES), which was starting to become vulnerable to brute-force attacks.
  • DES is an outdated symmetric key method of data encryption. DES works by using the same key to encrypt and decrypt a message, so both the sender and the receiver must know and use the same private key. DES has been superseded by the more secure AES algorithm.
  • Diffie-Hellman key exchange, also called exponential key exchange, is a method of digital encryption that uses numbers raised to specific powers to produce decryption keys on the basis of components that are never directly transmitted, making the task of a would-be code breaker mathematically overwhelming.
  • Elliptical curve cryptography (ECC) uses algebraic functions to generate security between key pairs. The resulting cryptographic algorithms can be faster and more efficient and can produce comparable levels of security with shorter cryptographic keys. This makes ECC algorithms a good choice for internet of things (IoT) devices and other products with limited computing resources.
  • Quantum key distribution (QKD) is a proposed method for encrypted messaging by which encryption keys are generated using a pair of entangled photons that are then transmitted separately to the message. Quantum entanglement enables the sender and receiver to know whether the encryption key has been intercepted or changed before the transmission even arrives. This is because, in the quantum realm, the very act of observing the transmitted information changes it. Once it has been determined that the encryption is secure and has not been intercepted, permission is given to transmit the encrypted message over a public internet channel.
  • RSA was first publicly described in 1977 by Ron Rivest, Adi Shamir and Leonard Adleman of the Massachusetts Institute of Technology (MIT), though the 1973 creation of a public key algorithm by British mathematician Clifford Cocks was kept classified by the U.K.'s Government Communications Headquarters (GCHQ) until 1997. Many protocols, like Secure Shell (SSH), OpenPGP, Secure/Multipurpose Internet Mail Extensions (S/MIME) and Secure Sockets Layer (SSL)/TLS, rely on RSA for encryption and digital signature functions.
Types of encryption algorithms
Popular encryption algorithms and hash functions

How to break encryption

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.  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.

Encryption backdoors

An encryption backdoor is a way to get around a system's authentication or encryption.  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.

Threats to IoT, mobile devices

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.

History of encryption

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.

This was last updated in June 2022

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