This article is about algorithms for encryption and decryption. For an overview of cryptographic technology in general, seeCryptography. For the music album, seeEncryption (album)."Encrypt" redirects here and is not to be confused withEncrypt (film).
A simple illustration of public-key cryptography, one of the most widely used forms of encryption
Incryptography,encryption (more specifically,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 asplaintext, into an alternative form known asciphertext. 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 apseudo-random encryptionkey generated by analgorithm. 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.[1] Modern encryption schemes use the concepts ofpublic-key[2] andsymmetric-key.[1] Modern encryption techniques ensure security because modern computers are inefficient at cracking the encryption.
One of the earliest forms of encryption is symbol replacement, which was first found in the tomb ofKhnumhotep 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.[3] One of the most famous military encryption developments was theCaesar 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.[4]
Around 800 AD, Arab mathematicianAl-Kindi developed the technique offrequency analysis – which was an attempt to crack ciphers systematically, including the Caesar cipher.[3] 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 thepolyalphabetic cipher, described byAl-Qalqashandi (1355–1418)[2] andLeon Battista Alberti (in 1465), which varied the substitution alphabet as encryption proceeded in order to confound such analysis.
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 theJefferson 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.[5]
A similar device to the Jefferson Disk, theM-94, was developed in 1917 independently by US Army Major Joseph Mauborne. This device was used in U.S. military communications until 1942.[6]
In World War II, the Axis powers used a more advanced version of the M-94 called theEnigma 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.[7] 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.
Today, encryption is used in the transfer of communication over theInternet for security and commerce.[1] As computing power continues to increase, computer encryption is constantly evolving to preventeavesdropping attacks.[8] One of the first "modern" cipher suites,DES, used a 56-bit key with 72,057,594,037,927,936 possibilities; it was cracked in 1999 byEFF's brute-forceDES cracker, which required 22 hours and 15 minutes to do so. Modern encryption standards often use stronger key sizes, such asAES (256-bit mode),TwoFish,ChaCha20-Poly1305,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 andbackdoors or by exploiting physical side effects throughSide-channel attacks. For example,RC4, a stream cipher, was cracked due to inherent biases and vulnerabilities in the cipher.
In the context of cryptography, encryption serves as a mechanism to ensureconfidentiality.[1] Since data may be visible on the Internet, sensitive information such aspasswords and personal communication may be exposed to potentialinterceptors.[1] The process of encrypting and decrypting messages involveskeys. The two main types of keys in cryptographic systems are symmetric-key and public-key (also known as asymmetric-key).[9][10]
Many complex cryptographic algorithms often use simplemodular arithmetic in their implementations.[11]
Insymmetric-key schemes,[12] 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.
Inpublic-key cryptography 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.[13] Public-key encryption was first described in a secret document in 1973;[14] beforehand, all encryption schemes were symmetric-key (also called private-key).[15]: 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.[16] The method became known as theDiffie-Hellman key exchange.
A publicly available public-key encryption application calledPretty Good Privacy (PGP) was written in 1991 byPhil Zimmermann, and distributed free of charge with source code. PGP was purchased bySymantec in 2010 and is regularly updated.[19]
Encryption has long been used bymilitaries andgovernments to facilitate secret communication. It is now commonly used in protecting information within many kinds of civilian systems. For example, theComputer 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.[20] 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.[21][22][23]Digital rights management systems, which prevent unauthorized use or reproduction of copyrighted material and protect software againstreverse engineering (see alsocopy protection), is another somewhat different example of using encryption on data at rest.[24]
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 calledcrypto-shredding. An example implementation of this method can be found oniOS devices, where the cryptographic key is kept in a dedicated 'effaceable storage'.[27] 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.
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.[28] For example, the original encryption key,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 tobrute force attacks.[29]
Quantum computing uses properties ofquantum 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.[30] 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 asemiprime 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] However, quantum computing can usequantum algorithms 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.[31] Other encryption techniques likeelliptic curve cryptography and symmetric key encryption are also vulnerable to quantum computing.[citation needed]
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.[32] Furthermore, quantum computing advancements will be able to be used in favor of encryption as well. TheNational Security Agency (NSA) is currently preparing post-quantum encryption standards for the future.[33] Quantum encryption promises a level of security that will be able to counter the threat of quantum computing.[32]
Encryption is an important tool but is not sufficient alone to ensure thesecurity orprivacy 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 acloud service for example.Homomorphic encryption andsecure multi-party computation are emerging techniques to compute encrypted data; these techniques are general andTuring 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,[34]stolen ciphertext attacks,[35] attacks on encryption keys,[36]insider attacks, data corruption or integrity attacks,[37] data destruction attacks, andransomware attacks. Data fragmentation[38] andactive defense[39] 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.[40]
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[41] 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.
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 amessage authentication code (MAC) or adigital signature usually done by ahashing algorithm or aPGP signature.Authenticated encryption algorithms are designed to provide both encryption and integrity protection together. Standards forcryptographic software andhardware 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 exampletraffic analysis,TEMPEST, orTrojan horse.[42]
Integrity protection mechanisms such asMACs anddigital signatures must be applied to the ciphertext when it is first created, typically on the same device used to compose the message, to protect a messageend-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 correctkeys and has not been tampered with. If an endpoint device has been configured to trust aroot certificate that an attacker controls, for example, then the attacker can both inspect and tamper with encrypted data by performing aman-in-the-middle attack anywhere along the message's path. The common practice ofTLS 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.[43]
Even when encryption correctly hides a message's content and it cannot be tampered with at rest or in transit, a message'slength is a form ofmetadata that can still leak sensitive information about the message. For example, the well-knownCRIME andBREACH attacks againstHTTPS wereside-channel attacks that relied on information leakage via the length of encrypted content.[44]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 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 increasingbandwidth overhead. Messages may be paddedrandomly ordeterministically, with each approach having different tradeoffs. Encrypting and padding messages to formpadded uniform random blobs or PURBs is a practice guaranteeing that the cipher text leaks nometadata about its cleartext's content, and leaks asymptotically minimalinformation via its length.[45]
^Abood, Omar G.; Guirguis, Shawkat K. (24 July 2018). "A Survey on Cryptography Algorithms".International Journal of Scientific and Research Publications.8 (7).doi:10.29322/IJSRP.8.7.2018.p7978.
^Sharma, Moolchand; Choudhary, Vikas; Bhatia, R. S.; Malik, Sahil; Raina, Anshuman; Khandelwal, Harshit (3 April 2021). "Leveraging the power of quantum computing for breaking RSA encryption".Cyber-Physical Systems.7 (2):73–92.doi:10.1080/23335777.2020.1811384.S2CID225312133.
^CryptoMoveArchived 2021-02-06 at theWayback Machine is the first technology to continuously move, mutate, and re-encrypt ciphertext as a form of data protection.
Tenzer, Theo (2021):SUPER SECRETO – The Third Epoch of Cryptography: Multiple, exponential, quantum-secure and above all, simple and practical Encryption for Everyone, Norderstedt,ISBN978-3-755-76117-4.
Lindell, Yehuda; Katz, Jonathan (2014),Introduction to modern cryptography, Hall/CRC,ISBN978-1466570269
