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{{short description|Process of converting plaintext to ciphertext}}
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[[File:Public key encryption keys.svg|alt=Text being turned into nonsense, then gets converted back to original|thumb|300x300px|A simple illustration of public-key cryptography, one of the most widely used forms of encryption]]
In [[Cryptography law|cryptography]], '''encryption''' (more specifically, [[Code|encoding]]) is the process of transforming  information in a way that, ideally, only authorized parties can decode. This process converts the original representation of the information, known as [[plaintext]], into an alternative form known as [[ciphertext]]. Despite its goal, encryption does not itself prevent interference but denies the intelligible content to a would-be interceptor.

For technical reasons, an encryption scheme usually uses a [[pseudo-random]] encryption [[Key (cryptography)|key]] generated by an [[algorithm]]. It is possible to decrypt the message without possessing the key but, for a well-designed encryption scheme, considerable computational resources and skills are required. An authorized recipient can easily decrypt the message with the key provided by the originator to recipients but not to unauthorized users.

Historically, various forms of encryption have been used to aid in cryptography. Early encryption techniques were often used in military messaging. Since then, new techniques have emerged and become commonplace in all areas of modern computing.<ref name=":1">{{Cite journal|last=Kessler|first=Gary|date=November 17, 2006|title=An Overview of Cryptography|url=https://www.garykessler.net/library/crypto.html|journal=Princeton University}}</ref> Modern encryption schemes use the concepts of [[Public-key cryptography|public-key]]<ref name=":5" /> and [[Symmetric-key algorithm|symmetric-key]].<ref name=":1" /> Modern encryption techniques ensure security because modern computers are inefficient at cracking the encryption.

== History ==

=== Ancient ===
One of the earliest forms of encryption is symbol replacement, which was first found in the tomb of [[Khnumhotep II]], who lived in 1900 BC Egypt. Symbol replacement encryption is “non-standard,” which means that the symbols require a cipher or key to understand. This type of early encryption was used throughout Ancient Greece and Rome for military purposes.<ref name=":4">{{Cite web|url=https://www.binance.vision/security/history-of-cryptography|title=History of Cryptography|website=Binance Academy|language=en|access-date=2020-04-02|archive-date=2020-04-26|archive-url=https://web.archive.org/web/20200426075650/https://www.binance.vision/security/history-of-cryptography|url-status=dead}}</ref>  One of the most famous military encryption developments was the [[Caesar cipher]], in which a plaintext letter is shifted a fixed number of positions along the alphabet to get the encoded letter. A message encoded with this type of encryption could be decoded with a fixed number on the Caesar cipher.'''<ref>{{Cite web|url=https://www.geeksforgeeks.org/caesar-cipher-in-cryptography/|title=Caesar Cipher in Cryptography|date=2016-06-02|website=GeeksforGeeks|language=en-US|access-date=2020-04-02}}</ref>'''

Around 800 AD, Arab mathematician [[Al-Kindi]] developed the technique of [[frequency analysis]] – which was an attempt to crack ciphers systematically, including the Caesar cipher.<ref name=":4" /> This technique looked at the frequency of letters in the encrypted message to determine the appropriate shift: for example, the most common letter in English text is E and is therefore likely to be represented by the letter that appears most commonly in the ciphertext. This technique was rendered ineffective by the [[polyalphabetic cipher]], described by [[Al-Qalqashandi]] (1355–1418)<ref name=":5">{{cite book |last1=Lennon |first1=Brian |url=https://books.google.com/books?id=jbpTDwAAQBAJ&pg=PT26 |title=Passwords: Philology, Security, Authentication |date=2018 |publisher=[[Harvard University Press]] |isbn=9780674985377 |page=26}}</ref> and [[Leon Battista Alberti]] (in 1465), which varied the substitution alphabet as encryption proceeded in order to confound such analysis.

=== 19th–20th century ===
Around 1790, [[Thomas Jefferson]] theorized a cipher to encode and decode messages to provide a more secure way of military correspondence. The cipher, known today as the Wheel Cipher or the [[Jefferson disk|Jefferson Disk]], although never actually built, was theorized as a spool that could jumble an English message up to 36 characters. The message could be decrypted by plugging in the jumbled message to a receiver with an identical cipher.'''<ref>{{Cite web|url=https://www.monticello.org/site/research-and-collections/wheel-cipher|title=Wheel Cipher|website=www.monticello.org|language=en|access-date=2020-04-02}}</ref>'''

A similar device to the Jefferson Disk, the [[M-94]], was developed in 1917 independently by US Army Major Joseph Mauborne. This device was used in U.S. military communications until 1942.<ref>{{Cite web|url=https://www.cryptomuseum.com/crypto/usa/m94/index.htm|title=M-94|website=www.cryptomuseum.com|access-date=2020-04-02}}</ref>

In World War II, the Axis powers used a more advanced version of the M-94 called the [[Enigma machine|Enigma Machine]]. The Enigma Machine was more complex because unlike the Jefferson Wheel and the M-94, each day the jumble of letters switched to a completely new combination. Each day's combination was only known by the Axis, so many thought the only way to break the code would be to try over 17,000 combinations within 24 hours.<ref>{{cite news |last1=Hern |first1=Alex |title=How did the Enigma machine work? |url=https://www.theguardian.com/technology/2014/nov/14/how-did-enigma-machine-work-imitation-game |work=The Guardian |date=14 November 2014 }}</ref> The Allies used computing power to severely limit the number of reasonable combinations they needed to check every day, leading to the breaking of the Enigma Machine.

=== Modern ===
Today, encryption is used in the transfer of communication over the [[Internet]] for security and commerce.<ref name=":1" /> As computing power continues to increase, computer encryption is constantly evolving to prevent [[eavesdropping]] attacks.<ref>{{cite magazine |last1=Newton |first1=Glen E. |title=The Evolution of Encryption |url=https://www.wired.com/insights/2013/05/the-evolution-of-encryption/ |magazine=Wired |others=Unisys |date=7 May 2013 }}</ref> One of the first "modern" cipher suites, [[Data Encryption Standard|DES]], used a 56-bit key with 72,057,594,037,927,936 possibilities; it was cracked in 1999 by [[Electronic Frontier Foundation|EFF's]] brute-force [[EFF DES cracker|DES cracker]], which required 22 hours and 15 minutes to do so. Modern encryption standards often use stronger key sizes, such as [[Advanced Encryption Standard|AES]] (256-bit mode), [[Twofish|TwoFish]], [[ChaCha20-Poly1305]], [[Serpent (cipher)|Serpent]] (configurable up to 512-bit). Cipher suites that use a 128-bit or higher key, like AES, will not be able to be brute-forced because the total amount of keys is 3.4028237e+38 possibilities. The most likely option for cracking ciphers with high key size is to find vulnerabilities in the cipher itself, like inherent biases and [[Backdoor (computing)|backdoors]] or by exploiting physical side effects through [[Side-channel attack|Side-channel attacks]]. For example, [[RC4]], a stream cipher, was cracked due to inherent biases and vulnerabilities in the cipher.

== Encryption in cryptography ==

In the context of cryptography, encryption serves as a mechanism to ensure [[Information security|confidentiality]].<ref name=":1"/> Since data may be visible on the Internet, sensitive information such as [[password]]s and personal communication may be exposed to potential [[Eavesdropping|interceptors]].<ref name=":1" /> The process of encrypting and decrypting messages involves [[Key (cryptography)|keys]]. The two main types of keys in cryptographic systems are symmetric-key and public-key (also known as asymmetric-key).<ref name=":0">{{cite book |doi=10.1016/B978-0-12-802324-2.00011-7 |chapter=Security Component Fundamentals for Assessment |title=Security Controls Evaluation, Testing, and Assessment Handbook |date=2016 |last1=Johnson |first1=Leighton |pages=531–627 |isbn=978-0-12-802324-2 }}</ref><ref name=":2">{{Cite web|last=Stubbs|first=Rob|title=Classification of Cryptographic Keys|url=https://www.cryptomathic.com/news-events/blog/classification-of-cryptographic-keys-functions-and-properties|access-date=2021-02-03|website=www.cryptomathic.com|language=en-us}}</ref>

Many complex cryptographic algorithms often use simple [[modular arithmetic]] in their implementations.<ref>{{Cite web|title=Chapter 3. Modular Arithmetic|url=https://www.doc.ic.ac.uk/~mrh/330tutor/ch03.html|access-date=2021-08-15|website=www.doc.ic.ac.uk|archive-date=2021-10-11|archive-url=https://web.archive.org/web/20211011110748/https://www.doc.ic.ac.uk/~mrh/330tutor/ch03.html|url-status=dead}}</ref>

===Types===

In [[Symmetric-key algorithm|symmetric-key]] schemes,<ref>{{Cite web|url=https://iaktueller.de/Collatz.py|title=Symmetric-key encryption software|access-date=2022-02-15|archive-date=2022-03-10|archive-url=https://web.archive.org/web/20220310103427/http://iaktueller.de/Collatz.py|url-status=dead}}</ref> the encryption and decryption keys are the same. Communicating parties must have the same key in order to achieve secure communication. The German Enigma Machine used a new symmetric-key each day for encoding and decoding messages.

In [[public-key encryption]] schemes, the encryption key is published for anyone to use and encrypt messages. However, only the receiving party has access to the decryption key that enables messages to be read.<ref>Bellare, Mihir. "Public-Key Encryption in a Multi-user Setting: Security Proofs and Improvements." Springer Berlin Heidelberg, 2000. p. 1.</ref> Public-key encryption was first described in a secret document in 1973;<ref>{{cite web|url=https://www.gchq.gov.uk/history/pke.html|archive-url=https://web.archive.org/web/20100519084635/https://www.gchq.gov.uk/history/pke.html|title=Public-Key Encryption – how GCHQ got there first!|publisher=gchq.gov.uk|archive-date=May 19, 2010}}</ref> beforehand, all encryption schemes were symmetric-key (also called private-key).<ref name="Goldreich">[[Oded Goldreich|Goldreich, Oded.]] Foundations of Cryptography: Volume 2, Basic Applications. Vol. 2. Cambridge university press, 2004.</ref>{{rp|478}} Although published subsequently, the work of Diffie and Hellman was published in a journal with a large readership, and the value of the methodology was explicitly described.<ref>{{citation | first1=Whitfield | last1=Diffie | first2=Martin | last2=Hellman | title=New directions in cryptography| pages=644–654| publisher=IEEE transactions on Information Theory| volume=22 | date=1976 }}</ref> The method became known as the [[Diffie–Hellman key exchange|Diffie-Hellman key exchange]].

[[RSA (cryptosystem)|RSA (Rivest–Shamir–Adleman)]] is another notable public-key [[cryptosystem]]. Created in 1978, it is still used today for applications involving [[digital signature]]s.<ref>{{Cite web |last=Kelly |first=Maria |date=December 7, 2009 |title=The RSA Algorithm: A Mathematical History of the Ubiquitous Cryptological Algorithm |url=https://www.sccs.swarthmore.edu/users/10/mkelly1/rsa.pdf |access-date=March 30, 2022 |website=Swarthmore College Computer Society |archive-date=March 31, 2022 |archive-url=https://web.archive.org/web/20220331215424/https://www.sccs.swarthmore.edu/users/10/mkelly1/rsa.pdf |url-status=dead }}</ref> Using [[number theory]], the RSA algorithm selects two [[prime number]]s, which help generate both the encryption and decryption keys.<ref>{{cite journal |last1=Prasetyo |first1=Deny |last2=Widianto |first2=Eko Didik |last3=Indasari |first3=Ike Pratiwi |title=Short Message Service Encoding Using the Rivest-Shamir-Adleman Algorithm |journal=Jurnal Online Informatika |date=6 September 2019 |volume=4 |issue=1 |pages=39 |doi=10.15575/join.v4i1.264 |doi-access=free }}</ref>

A publicly available public-key encryption application called [[Pretty Good Privacy]] (PGP) was written in 1991 by [[Phil Zimmermann]], and distributed free of charge with source code. PGP was purchased by [[NortonLifeLock|Symantec]] in 2010 and is regularly updated.<ref>{{Cite web|url=https://www.computerworld.com/article/2517739/symantec-buys-encryption-specialist-pgp-for--300m.html|title=Symantec buys encryption specialist PGP for $300M|first=Jeremy|last=Kirk|date=April 29, 2010|website=Computerworld|access-date=January 31, 2020|archive-date=January 31, 2020|archive-url=https://web.archive.org/web/20200131201636/https://www.computerworld.com/article/2517739/symantec-buys-encryption-specialist-pgp-for--300m.html|url-status=dead}}</ref>

== Uses ==

Encryption has long been used by [[Military|militaries]] and [[government]]s to facilitate secret communication. It is now commonly used in protecting information within many kinds of civilian systems. For example, the [[Computer Security Institute]] reported that in 2007, 71% of companies surveyed used encryption for some of their data in transit, and 53% used encryption for some of their data in storage.<ref>Robert Richardson, 2008 CSI Computer Crime and Security Survey at 19.[https://i.cmpnet.com/v2.gocsi.com/pdf/CSIsurvey2008.pdf i.cmpnet.com]</ref> Encryption can be used to protect data "at rest", such as information stored on computers and storage devices (e.g. [[USB flash drives]]). In recent years, there have been numerous reports of confidential data, such as customers' personal records, being exposed through loss or theft of laptops or backup drives; encrypting such files at rest helps protect them if physical security measures fail.<ref name="KeaneWhyStolen16">{{cite web |url=https://www.pcworld.com/article/3021316/security/why-stolen-laptops-still-cause-data-breaches-and-whats-being-done-to-stop-them.html |title=Why stolen laptops still cause data breaches, and what's being done to stop them |author=Keane, J. |work=PCWorld |publisher=IDG Communications, Inc |date=13 January 2016 |access-date=8 May 2018}}</ref><ref name="CastriconeFebruary18">{{cite web |url=https://www.natlawreview.com/article/february-2-2018-health-care-group-news-35-m-ocr-settlement-five-breaches-affecting |title= Health Care Group News: $3.5 M OCR Settlement for Five Breaches Affecting Fewer Than 500 Patients Each |author=Castricone, D.M. |work=The National Law Review |publisher=National Law Forum LLC |date=2 February 2018 |access-date=8 May 2018}}</ref><ref name="BekProtect16">{{cite web |url=https://blog.westerndigital.com/protect-your-company-from-theft-self-encrypting-drives/ |title=Protect Your Company from Theft: Self Encrypting Drives |author=Bek, E. |work=Western Digital Blog |publisher=Western Digital Corporation |date=19 May 2016 |access-date=8 May 2018}}</ref> [[Digital rights management]] systems, which prevent unauthorized use or reproduction of copyrighted material and protect software against [[reverse engineering]] (see also [[copy protection]]), is another somewhat different example of using encryption on data at rest.<ref>{{cite web|url=https://www.eff.org/issues/drm|title=DRM|work=Electronic Frontier Foundation}}</ref>

Encryption is also used to protect data in transit, for example data being transferred via [[computer network|networks]] (e.g. the Internet, [[e-commerce]]), [[mobile telephone]]s, [[wireless microphone]]s, [[wireless intercom]] systems, [[Bluetooth]] devices and bank [[automatic teller machine]]s. There have been numerous reports of data in transit being intercepted in recent years.<ref>Fiber Optic Networks Vulnerable to Attack, Information Security Magazine, November 15, 2006, Sandra Kay Miller</ref> Data should also be encrypted when transmitted across networks in order to protect against [[eavesdropping]] of network traffic by unauthorized users.<ref>{{Cite web|url=https://security.berkeley.edu/data-encryption-transit-guideline|title=Data Encryption in Transit Guideline |website=Berkeley Information Security Office |url-status=live |archive-url= https://web.archive.org/web/20231205085812/https://security.berkeley.edu/data-encryption-transit-guideline |archive-date= Dec 5, 2023 }}</ref>
<!-- If edited, this may be more appropriate in this section.

 With the increased use of digital archives because of evolving multimedia sources, comes with it an immense amount of data.<ref>{{cite journal |last1=Park |first1=Sang Bae |title=Security Requirements for Multimedia Archives |journal=Advances in Multimedia |date=3 August 2015 |volume=2015 |pages=e956416 |doi=10.1155/2015/956416 }}</ref> When two different parties for an entity like a multimedia source have access to all this data, they need to protect it-and they use a Symmetric Key when they want to be able to have only the two parties relay this information. Essentially the person/group sending the information has to have the same algorithm that the receiver does in order to receive it.<ref>{{cite journal |last1=Dent |first1=Alexander W. |title=A survey of certificateless encryption schemes and security models |journal=International Journal of Information Security |date=October 2008 |volume=7 |issue=5 |pages=349–377 |doi=10.1007/s10207-008-0055-0 }}</ref> However with this ability to have two parties to relay what now is encrypted data makes it the most susceptible encryption type to be targeted for an attack, opposed to a Public Key.
-->

=== Data erasure ===
{{main|Data erasure}}
Conventional methods for permanently deleting data from a storage device involve overwriting the device's whole content with zeros, ones, or other patterns – a process which can take a significant amount of time, depending on the capacity and the type of storage medium. Cryptography offers a way of making the erasure almost instantaneous. This method is called [[crypto-shredding]]. An example implementation of this method can be found on [[iOS]] devices, where the cryptographic key is kept in a dedicated '[[wikt:efface|effaceable]] storage'.<ref>{{Cite web|url=https://support.apple.com/guide/security/welcome/web
|title=Welcome|website=Apple Support}}</ref> Because the key is stored on the same device, this setup on its own does not offer full privacy or security protection if an unauthorized person gains physical access to the device.

== Limitations ==
Encryption is used in the 21st century to protect digital data and information systems. As computing power increased over the years, encryption technology has only become more advanced and secure. However, this advancement in technology has also exposed a potential limitation of today's encryption methods.

The length of the encryption key is an indicator of the strength of the encryption method.<ref>{{cite journal |last1=Abood |first1=Omar G. |last2=Guirguis |first2=Shawkat K. |title=A Survey on Cryptography Algorithms |journal=International Journal of Scientific and Research Publications (IJSRP) |date=24 July 2018 |volume=8 |issue=7 |doi=10.29322/IJSRP.8.7.2018.p7978 }}</ref> For example, the original encryption key, [[Data Encryption Standard|DES]] (Data Encryption Standard), was 56 bits, meaning it had 2^56 combination possibilities. With today's computing power, a 56-bit key is no longer secure, being vulnerable to [[Brute-force attack|brute force attacks]].<ref>{{Cite web |title=Encryption methods: An overview |url=https://www.ionos.com/digitalguide/server/security/encryption-methods-an-overview/ |access-date=2022-10-07 |website=IONOS Digital Guide |language=en}}</ref>

[[Quantum computing]] uses properties of [[quantum mechanics]] in order to process large amounts of data simultaneously. Quantum computing has been found to achieve computing speeds thousands of times faster than today's supercomputers.<ref>{{Cite web|date=2020-05-01|title=Quantum computers vastly outperform supercomputers when it comes to energy efficiency|url=https://physicsworld.com/a/quantum-computers-vastly-outperform-supercomputers-when-it-comes-to-energy-efficiency/|access-date=2021-05-02|website=Physics World|language=en-GB}}</ref> This computing power presents a challenge to today's encryption technology. For example, RSA encryption uses the multiplication of very large prime numbers to create a [[semiprime number]] for its public key. Decoding this key without its private key requires this semiprime number to be factored, which can take a very long time to do with modern computers. It would take a supercomputer anywhere between weeks to months to factor in this key.{{citation needed|date=June 2020}} However, quantum computing can use [[quantum algorithm]]s to factor this semiprime number in the same amount of time it takes for normal computers to generate it. This would make all data protected by current public-key encryption vulnerable to quantum computing attacks.<ref>{{cite journal |last1=Sharma |first1=Moolchand |last2=Choudhary |first2=Vikas |last3=Bhatia |first3=R. S. |last4=Malik |first4=Sahil |last5=Raina |first5=Anshuman |last6=Khandelwal |first6=Harshit |title=Leveraging the power of quantum computing for breaking RSA encryption |journal=Cyber-Physical Systems |date=3 April 2021 |volume=7 |issue=2 |pages=73–92 |doi=10.1080/23335777.2020.1811384 |s2cid=225312133 }}</ref> Other encryption techniques like [[Elliptic-curve cryptography|elliptic curve cryptography]] and symmetric key encryption are also vulnerable to quantum computing.{{citation needed|date=July 2020}}

While quantum computing could be a threat to encryption security in the future, quantum computing as it currently stands is still very limited. Quantum computing currently is not commercially available, cannot handle large amounts of code, and only exists as computational devices, not computers.<ref name=":3">{{cite journal |last1=Solenov |first1=Dmitry |last2=Brieler |first2=Jay |last3=Scherrer |first3=Jeffrey F. |title=The Potential of Quantum Computing and Machine Learning to Advance Clinical Research and Change the Practice of Medicine |journal=Missouri Medicine |date=2018 |volume=115 |issue=5 |pages=463–467 |pmc=6205278 |pmid=30385997 }}</ref> Furthermore, quantum computing advancements will be able to be used in favor of encryption as well. The [[National Security Agency]] (NSA) is currently preparing post-quantum encryption standards for the future.<ref>{{Cite web|title=Post-Quantum Cybersecurity Resources|url=https://www.nsa.gov/what-we-do/cybersecurity/post-quantum-cybersecurity-resources/|access-date=2021-01-16|website=www.nsa.gov|archive-date=2021-01-18|archive-url=https://web.archive.org/web/20210118015943/https://www.nsa.gov/what-we-do/cybersecurity/post-quantum-cybersecurity-resources/|url-status=dead}}</ref> Quantum encryption promises a level of security that will be able to counter the threat of quantum computing.<ref name=":3" />

== Attacks and countermeasures ==

Encryption is an important tool but is not sufficient alone to ensure the [[Information security|security]] or [[Information privacy|privacy]] of sensitive information throughout its lifetime. Most applications of encryption protect information only at rest or in transit, leaving sensitive data in clear text and potentially vulnerable to improper disclosure during processing, such as by a [[Cloud computing|cloud]] service for example. [[Homomorphic encryption]] and [[secure multi-party computation]] are emerging techniques to compute encrypted data; these techniques are general and [[Turing completeness|Turing complete]] but incur high computational and/or communication costs.

In response to encryption of data at rest, cyber-adversaries have developed new types of attacks. These more recent threats to encryption of data at rest include cryptographic attacks,<ref>{{cite web |others=Discussion of encryption weaknesses for petabyte scale datasets |url=https://www.ssrc.ucsc.edu/Papers/li-fast13.pdf |website=www.ssrc.ucsc.edu |title=Horus: Fine-Grained Encryption-Based Security for Large-Scale Storage |author=Yan Li |author2=Nakul Sanjay Dhotre |author3=Yasuhiro Ohara |author4=Thomas M. Kroeger |author5=Ethan L. Miller |author6=Darrell D. E. Long}}</ref> [[Ciphertext stealing|stolen ciphertext attacks]],<ref>{{Cite web |url=https://robertheaton.com/2013/07/29/padding-oracle-attack/ |title=The Padding Oracle Attack – why crypto is terrifying|website=Robert Heaton |access-date=2016-12-25}}</ref> attacks on encryption keys,<ref>{{Cite news |url=https://arstechnica.com/security/2016/08/researchers-crack-open-unusually-advanced-malware-that-hid-for-5-years/ |title=Researchers crack open unusually advanced malware that hid for 5 years |newspaper=Ars Technica |access-date=2016-12-25}}</ref> [[Insider threat|insider attacks]], data corruption or integrity attacks,<ref>{{Cite news|url=https://arstechnica.com/security/2016/08/new-attack-steals-private-crypto-keys-by-corrupting-data-in-computer-memory/|title=New cloud attack takes full control of virtual machines with little effort|newspaper=Ars Technica|access-date=2016-12-25}}</ref> data destruction attacks, and [[ransomware]] attacks. Data fragmentation<ref>Examples of data fragmentation technologies include [[Tahoe-LAFS]] and [https://storj.io/index.html Storj].</ref> and [[Active Defense|active defense]]<ref>{{Cite news|url=https://blog.cryptomove.com/what-does-active-defense-mean-4ecff93c4bc4|title=What does 'Active Defense' mean?|last=Burshteyn|first=Mike|date=2016-12-22|newspaper=CryptoMove|access-date=2016-12-25}}{{Dead link|date=April 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> data protection technologies attempt to counter some of these attacks, by distributing, moving, or mutating ciphertext so it is more difficult to identify, steal, corrupt, or destroy.<ref>[https://www.cryptomove.com CryptoMove] {{Webarchive|url=https://web.archive.org/web/20210206131311/https://www.cryptomove.com/ |date=2021-02-06 }} is the first technology to continuously move, mutate, and re-encrypt ciphertext as a form of data protection.</ref>

== The debate around encryption ==
The question of balancing the need for national security with the right to privacy has been debated for years, since encryption has become critical in today's digital society. The modern encryption debate<ref>{{Cite web |last= Catania |first= Simone |date=2022-11-02 |title=The Modern Encryption Debate: What's at Stake? |url=https://circleid.com/posts/20221102-the-modern-encryption-debate-whats-at-stake|website=CircleID |language=en}}</ref> started around the '90s when US government tried to ban cryptography because, according to them, it would threaten national security. The debate is polarized around two opposing views. Those who see strong encryption as a problem making it easier for criminals to hide their illegal acts online and others who argue that encryption keep digital communications safe. The debate heated up in 2014, when Big Tech like Apple and Google set encryption by default in their devices. This was the start of a series of controversies that puts governments, companies and internet users at stake.

=== Integrity protection of Ciphertexts ===

Encryption, by itself, can protect the confidentiality of messages, but other techniques are still needed to protect the integrity and authenticity of a message; for example, verification of a [[message authentication code]] (MAC) or a [[digital signature]] usually done by a [[Hash function|hashing algorithm]] or a [[Pretty Good Privacy|PGP signature]]. [[Authenticated encryption]] algorithms are designed to provide both encryption and integrity protection together. Standards for [[cryptographic software]] and [[Hardware encryption|hardware to perform encryption]] are widely available, but successfully using encryption to ensure security may be a challenging problem. A single error in system design or execution can allow successful attacks. Sometimes an adversary can obtain unencrypted information without directly undoing the encryption. See for example [[traffic analysis]], [[Tempest (codename)|TEMPEST]], or [[Trojan horse (computing)|Trojan horse]].<ref>{{cite web|url=https://usa.kaspersky.com/internet-security-center/threats/trojans#.VV3oaWDTvfY|title=What is a Trojan Virus – Malware Protection – Kaspersky Lab US|date=3 October 2023 }}</ref>

Integrity protection mechanisms such as [[message authentication code|MACs]] and [[digital signature]]s must be applied to the ciphertext when it is first created, typically on the same device used to compose the message, to protect a message [[End-to-end principle|end-to-end]] along its full transmission path; otherwise, any node between the sender and the encryption agent could potentially tamper with it. Encrypting at the time of creation is only secure if the encryption device itself has correct [[Key (cryptography)|keys]] and has not been tampered with. If an endpoint device has been configured to trust a [[root certificate]] that an attacker controls, for example, then the attacker can both inspect and tamper with encrypted data by performing a [[man-in-the-middle attack]] anywhere along the message's path. The common practice of [[Transport Layer Security#TLS interception|TLS interception]] by network operators represents a controlled and institutionally sanctioned form of such an attack, but countries have also attempted to employ such attacks as a form of control and censorship.<ref>{{cite news|url=https://thehackernews.com/2019/07/kazakhstan-https-security-certificate.html|title=Kazakhstan Begins Intercepting HTTPS Internet Traffic Of All Citizens Forcefully|first1=Mohit|last1=Kumar|date=July 2019|publisher=The Hacker News}}</ref>

=== Ciphertext length and padding ===

{{main| Padding (cryptography)}}

Even when encryption correctly hides a message's content and it cannot be tampered with at rest or in transit, a message's ''length'' is a form of [[metadata]] that can still leak sensitive information about the message. For example, the well-known [[CRIME]] and [[BREACH]] attacks against [[HTTPS]] were [[side-channel attack]]s that relied on information leakage via the length of encrypted content.<ref>{{cite report|url=https://tools.ietf.org/html/rfc7457|title= Summarizing Known Attacks on Transport Layer Security (TLS) and Datagram TLS (DTLS)|first1=Y.|last1=Sheffer|first2=R.|last2=Holz|first3=P.|last3=Saint-Andre|date= February 2015}}</ref> [[Traffic analysis]] is a broad class of techniques that often employs message lengths to infer sensitive implementation about traffic flows by aggregating information about a large number of messages.

[[Padding (cryptography)|Padding]] a message's payload before encrypting it can help obscure the cleartext's true length, at the cost of increasing the ciphertext's size and introducing or increasing [[Overhead (computing)|bandwidth overhead]]. Messages may be padded [[Padding (cryptography)#Randomized padding|randomly]] or [[Padding (cryptography)#Deterministic padding|deterministically]], with each approach having different tradeoffs. Encrypting and padding messages to form [[PURB (cryptography)|padded uniform random blobs or PURBs]] is a practice guaranteeing that the cipher text leaks no [[metadata]] about its cleartext's content, and leaks asymptotically minimal <math>O(\log\log M)</math> [[Entropy (information theory)|information]] via its length.<ref>{{cite journal|url=https://petsymposium.org/2019/files/papers/issue4/popets-2019-0056.pdf|title=Reducing Metadata Leakage from Encrypted Files and Communication with PURBs|first1=Kirill|last1=Nikitin|first2=Ludovic|last2=Barman|first3=Wouter|last3=Lueks|first4=Matthew|last4=Underwood|first5=Jean-Pierre|last5=Hubaux|first6=Bryan|last6=Ford|journal=Proceedings on Privacy Enhancing Technologies (PoPETS)|volume=2019|issue=4|pages=6–33|doi=10.2478/popets-2019-0056|year=2019|arxiv=1806.03160 |s2cid=47011059|doi-access=free}}</ref>

== See also ==
{{div col |colwidth=18em}}
* [[Cryptosystem]]
* [[Cold boot attack]]
* [[Cryptography standards]]
* [[Cyberspace Electronic Security Act]] (US)
* [[Dictionary attack]]
* [[Disk encryption]]
* [[Encrypted function]]
* [[Enigma machine]]
* [[Export of cryptography]]
* [[Geo-blocking]]
* [[Indistinguishability obfuscation]]
* [[Key management]]
* [[Multiple encryption]]
* [[Information-theoretic security#Physical layer encryption|Physical Layer Encryption]]
* [[Pretty Good Privacy]]
* [[Post-quantum cryptography]]
* [[Rainbow table]]
* [[Rotor machine]]
* [[Side-channel attack]]
* [[Substitution cipher]]
* [[Television encryption]]
* [[Tokenization (data security)]]
{{div col end}}

==References==
{{reflist}}

==Further reading==
* {{Citation | last = Fouché Gaines | first = Helen | author-link = Helen Fouché Gaines | title = Cryptanalysis: A Study of Ciphers and Their Solution | place = New York | publisher = Dover Publications Inc | year = 1939 | isbn = 978-0486200972 | url-access = registration | url = https://archive.org/details/cryptanalysis00hele  |ref=none}}
* [[David Kahn (writer)|Kahn, David]] (1967), ''The Codebreakers - The Story of Secret Writing'' ({{ISBN|0-684-83130-9}})
* [[Bart Preneel|Preneel, Bart]] (2000), "Advances in Cryptology – EUROCRYPT 2000", Springer Berlin Heidelberg, {{ISBN|978-3-540-67517-4}}
* [[Abraham Sinkov|Sinkov, Abraham]] (1966): ''Elementary Cryptanalysis: A Mathematical Approach'', Mathematical Association of America. {{ISBN|0-88385-622-0}}
* Tenzer, Theo (2021): ''SUPER SECRETO – The Third Epoch of Cryptography: Multiple, exponential, quantum-secure and above all, simple and practical Encryption for Everyone'', Norderstedt, {{isbn|978-3-755-76117-4}}.
* {{Citation | last1 =Lindell | first1 = Yehuda|last2=Katz |first2=Jonathan | title = Introduction to modern cryptography | publisher =  Hall/CRC | year = 2014 | isbn =  978-1466570269  |ref=none}}
* {{Citation | last1 = Ermoshina | first1 = Ksenia | last2= Musiani| first2= Francesca| title =  Concealing for Freedom: The Making of Encryption, Secure Messaging and Digital Liberties (Foreword by Laura DeNardis)(open access) | place = Manchester, UK | publisher = matteringpress.org | year = 2022 | isbn = 978-1-912729-22-7 | url-access = registration |url=https://www.matteringpress.org/wp-content/uploads/2022/05/Concealing-for-Freedom-ePDF.pdf |archive-url=https://web.archive.org/web/20220602103410/https://www.matteringpress.org/wp-content/uploads/2022/05/Concealing-for-Freedom-ePDF.pdf |archive-date=2022-06-02  |ref=none}}

== External links ==
* {{Wiktionary-inline|encryption}}
* {{Commonscat-inline|Cryptographic algorithms|position=}}

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