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Original Translated
Introduction to Cryptography de Introduction to Cryptography
Cryptography de Cryptography
Cryptography or cryptology (from de Cryptography or cryptology (from
secure communicationin the presence of third parties called de secure communicationin the presence of third parties called
information securitysuch as data de information securitysuch as data
confidentiality, de confidentiality,
data integrity, de data integrity,
authentication, and de authentication, and
non-repudiation [4] are central to modern cryptography. de non-repudiation [4] are central to modern cryptography.
Modern cryptography exists at the intersection of the disciplines of de Modern cryptography exists at the intersection of the disciplines of
mathematics, de mathematics,
computer science, de computer science,
electrical engineering, de electrical engineering,
communication science, and de communication science, and
physics. de physics.
Applications of cryptography include de Applications of cryptography include
electronic commerce, de electronic commerce,
chip-based payment cards, de chip-based payment cards,
digital currencies, de digital currencies,
computer passwords, and de computer passwords, and
military communications. de military communications.
Cryptography prior to the modern age was effectively synonymous with de Cryptography prior to the modern age was effectively synonymous with
nonsense. de nonsense.
The originator of an encrypted message shares the decoding technique only with intended recipients to preclude access from adversaries. de The originator of an encrypted message shares the decoding technique only with intended recipients to preclude access from adversaries.
The cryptography literature de The cryptography literature
rotor cipher machinesin de rotor cipher machinesin
World WarIand the advent of de World WarIand the advent of
computersin de computersin
World WarII, the methods used to carry out cryptology have become increasingly complex and its application more widespread. de World WarII, the methods used to carry out cryptology have become increasingly complex and its application more widespread.
Modern cryptography is heavily based on mathematical theory and computer science practice; cryptographic de Modern cryptography is heavily based on mathematical theory and computer science practice; cryptographic
algorithmsare designed around de algorithmsare designed around
computational hardness assumptions, making such algorithms hard to break in practice by any adversary. de computational hardness assumptions, making such algorithms hard to break in practice by any adversary.
It is theoretically possible to break such a system, but it is infeasible to do so by any known practical means. de It is theoretically possible to break such a system, but it is infeasible to do so by any known practical means.
These schemes are therefore termed computationally secure; theoretical advances, e.g., improvements in de These schemes are therefore termed computationally secure; theoretical advances, e.g., improvements in
integer factorizationalgorithms, and faster computing technology require these solutions to be continually adapted. de integer factorizationalgorithms, and faster computing technology require these solutions to be continually adapted.
There exist de There exist
information-theoretically secureschemes that provably cannot be broken even with unlimited computing power—an example is the de information-theoretically secureschemes that provably cannot be broken even with unlimited computing power—an example is the
one-time pad—but these schemes are more difficult to use in practice than the best theoretically breakable but computationally secure mechanisms. de one-time pad—but these schemes are more difficult to use in practice than the best theoretically breakable but computationally secure mechanisms.
The growth of cryptographic technology has raised a number of legal issues in the information age. de The growth of cryptographic technology has raised a number of legal issues in the information age.
Cryptography’s potential for use as a tool for de Cryptography’s potential for use as a tool for
espionageand de espionageand
digital rights managementand de digital rights managementand
Terminology de Terminology
Until modern times, cryptography referred almost exclusively to de Until modern times, cryptography referred almost exclusively to
encryption, which is the process of converting ordinary information (called de encryption, which is the process of converting ordinary information (called
plaintext) into unintelligible form (called de plaintext) into unintelligible form (called
ciphertext). de ciphertext).
Decryption is the reverse, in other words, moving from the unintelligible ciphertext back to plaintext. de Decryption is the reverse, in other words, moving from the unintelligible ciphertext back to plaintext.
A de A
cypher) is a pair of algorithms that create the encryption and the reversing decryption. de cypher) is a pair of algorithms that create the encryption and the reversing decryption.
The detailed operation of a cipher is controlled both by the algorithm and in each instance by a “key“. de The detailed operation of a cipher is controlled both by the algorithm and in each instance by a “key“.
The key is a secret (ideally known only to the communicants), usually a short string of characters, which is needed to decrypt the ciphertext. de The key is a secret (ideally known only to the communicants), usually a short string of characters, which is needed to decrypt the ciphertext.
Formally, a “cryptosystem” is the ordered list of elements of finite possible plaintexts, finite possible cyphertexts, finite possible keys, and the encryption and decryption algorithms which correspond to each key. de Formally, a “cryptosystem” is the ordered list of elements of finite possible plaintexts, finite possible cyphertexts, finite possible keys, and the encryption and decryption algorithms which correspond to each key.
Keys are important both formally and in actual practice, as ciphers without variable keys can be trivially broken with only the knowledge of the cipher used and are therefore useless (or even counter-productive) for most purposes. de Keys are important both formally and in actual practice, as ciphers without variable keys can be trivially broken with only the knowledge of the cipher used and are therefore useless (or even counter-productive) for most purposes.
Historically, ciphers were often used directly for encryption or decryption without additional procedures such as de Historically, ciphers were often used directly for encryption or decryption without additional procedures such as
authenticationor integrity checks. de authenticationor integrity checks.
There are two kinds of cryptosystems: de There are two kinds of cryptosystems:
symmetricand de symmetricand
asymmetric. de asymmetric.
In symmetric systems the same key (the secret key) is used to encrypt and decrypt a message. de In symmetric systems the same key (the secret key) is used to encrypt and decrypt a message.
Data manipulation in symmetric systems is faster than asymmetric systems as they generally use shorter key lengths. de Data manipulation in symmetric systems is faster than asymmetric systems as they generally use shorter key lengths.
Asymmetric systems use a public key to encrypt a message and a private key to decrypt it. de Asymmetric systems use a public key to encrypt a message and a private key to decrypt it.
Use of asymmetric systems enhances the security of communication. de Use of asymmetric systems enhances the security of communication.
Examples of asymmetric systems include RSA (Rivest-Shamir-Adleman), and ECC (Elliptic Curve Cryptography). de Examples of asymmetric systems include RSA (Rivest-Shamir-Adleman), and ECC (Elliptic Curve Cryptography).
Symmetric models include the commonly used AES (Advanced Encryption Standard) which replaced the older DES (Data Encryption Standard). de Symmetric models include the commonly used AES (Advanced Encryption Standard) which replaced the older DES (Data Encryption Standard).
In de In
colloquialuse, the term “code” is often used to mean any method of encryption or concealment of meaning. de colloquialuse, the term “code” is often used to mean any method of encryption or concealment of meaning.
However, in cryptography, de However, in cryptography,
codehas a more specific meaning. de codehas a more specific meaning.
It means the replacement of a unit of plaintext (i.e., a meaningful word or phrase) with a de It means the replacement of a unit of plaintext (i.e., a meaningful word or phrase) with a
code word(for example, “wallaby” replaces “attack at dawn”). de code word(for example, “wallaby” replaces “attack at dawn”).
Cryptanalysisis the term used for the study of methods for obtaining the meaning of encrypted information without access to the key normally required to do so; i.e., it is the study of how to crack encryption algorithms or their implementations. de Cryptanalysisis the term used for the study of methods for obtaining the meaning of encrypted information without access to the key normally required to do so; i.e., it is the study of how to crack encryption algorithms or their implementations.
Some use the terms de Some use the terms
cryptographyand de cryptographyand
cryptologyinterchangeably in English, while others (including US military practice generally) use de cryptologyinterchangeably in English, while others (including US military practice generally) use
cryptographyto refer specifically to the use and practice of cryptographic techniques and de cryptographyto refer specifically to the use and practice of cryptographic techniques and
cryptologyto refer to the combined study of cryptography and cryptanalysis. de cryptologyto refer to the combined study of cryptography and cryptanalysis.
English is more flexible than several other languages in which de English is more flexible than several other languages in which
cryptology(done by cryptologists) is always used in the second sense above. de cryptology(done by cryptologists) is always used in the second sense above.
RFC2828advises thatsteganographyis sometimes included in cryptology. de RFC2828advises thatsteganographyis sometimes included in cryptology.
The study of characteristics of languages that have some application in cryptography or cryptology (e.g. frequency data, letter combinations, universal patterns, etc.) is called cryptolinguistics. de The study of characteristics of languages that have some application in cryptography or cryptology (e.g. frequency data, letter combinations, universal patterns, etc.) is called cryptolinguistics.
History of Cryptography de History of Cryptography
Before the modern era, cryptography focused on message confidentiality (i.e., encryption)—conversion of de Before the modern era, cryptography focused on message confidentiality (i.e., encryption)—conversion of
messagesfrom a comprehensible form into an incomprehensible one and back again at the other end, rendering it unreadable by interceptors or eavesdroppers without secret knowledge (namely the key needed for decryption of that message). de messagesfrom a comprehensible form into an incomprehensible one and back again at the other end, rendering it unreadable by interceptors or eavesdroppers without secret knowledge (namely the key needed for decryption of that message).
Encryption attempted to ensure de Encryption attempted to ensure
secrecyin de secrecyin
communications, such as those of de communications, such as those of
spies, military leaders, and de spies, military leaders, and
diplomats. de diplomats.
In recent decades, the field has expanded beyond confidentiality concerns to include techniques for message integrity checking, sender/receiver identity de In recent decades, the field has expanded beyond confidentiality concerns to include techniques for message integrity checking, sender/receiver identity
authentication, de authentication,
digital signatures, de digital signatures,
interactive proofsand de interactive proofsand
secure computation, among others. de secure computation, among others.
Computer era de Computer era
Prior to the early 20th century, cryptography was mainly concerned with de Prior to the early 20th century, cryptography was mainly concerned with
linguisticand de linguisticand
lexicographicpatterns. de lexicographicpatterns.
Since then the emphasis has shifted, and cryptography now makes extensive use of mathematics, including aspects of de Since then the emphasis has shifted, and cryptography now makes extensive use of mathematics, including aspects of
information theory, de information theory,
computational complexity, de computational complexity,
statistics, de statistics,
combinatorics, de combinatorics,
abstract algebra, de abstract algebra,
number theory, and finite mathematics generally. de number theory, and finite mathematics generally.
Cryptography is also a branch of de Cryptography is also a branch of
engineering, but an unusual one since it deals with active, intelligent, and malevolent opposition (see cryptographic engineering and de engineering, but an unusual one since it deals with active, intelligent, and malevolent opposition (see cryptographic engineering and
security engineering); other kinds of engineering (e.g., civil or chemical engineering) need deal only with neutral natural forces. de security engineering); other kinds of engineering (e.g., civil or chemical engineering) need deal only with neutral natural forces.
There is also active research examining the relationship between cryptographic problems and de There is also active research examining the relationship between cryptographic problems and
quantum physics(see de quantum physics(see
quantum cryptographyand de quantum cryptographyand
quantum computer). de quantum computer).
Just as the development of digital computers and electronics helped in cryptanalysis, it made possible much more complex ciphers. de Just as the development of digital computers and electronics helped in cryptanalysis, it made possible much more complex ciphers.
Furthermore, computers allowed for the encryption of any kind of data representable in any binary format, unlike classical ciphers which only encrypted written language texts; this was new and significant. de Furthermore, computers allowed for the encryption of any kind of data representable in any binary format, unlike classical ciphers which only encrypted written language texts; this was new and significant.
Computer use has thus supplanted linguistic cryptography, both for cipher design and cryptanalysis. de Computer use has thus supplanted linguistic cryptography, both for cipher design and cryptanalysis.
Many computer ciphers can be characterized by their operation on de Many computer ciphers can be characterized by their operation on
binary de binary
bitsequences (sometimes in groups or blocks), unlike classical and mechanical schemes, which generally manipulate traditional characters (i.e., letters and digits) directly. de bitsequences (sometimes in groups or blocks), unlike classical and mechanical schemes, which generally manipulate traditional characters (i.e., letters and digits) directly.
However, computers have also assisted cryptanalysis, which has compensated to some extent for increased cipher complexity. de However, computers have also assisted cryptanalysis, which has compensated to some extent for increased cipher complexity.
Nonetheless, good modern ciphers have stayed ahead of cryptanalysis; it is typically the case that use of a quality cipher is very efficient (i.e., fast and requiring few resources, such as memory or CPU capability), while breaking it requires an effort many orders of magnitude larger, and vastly larger than that required for any classical cipher, making cryptanalysis so inefficient and impractical as to be effectively impossible. de Nonetheless, good modern ciphers have stayed ahead of cryptanalysis; it is typically the case that use of a quality cipher is very efficient (i.e., fast and requiring few resources, such as memory or CPU capability), while breaking it requires an effort many orders of magnitude larger, and vastly larger than that required for any classical cipher, making cryptanalysis so inefficient and impractical as to be effectively impossible.
Advent of modern cryptography de Advent of modern cryptography
Cryptanalysisof the new mechanical devices proved to be both difficult and laborious. de Cryptanalysisof the new mechanical devices proved to be both difficult and laborious.
In the United Kingdom, cryptanalytic efforts at de In the United Kingdom, cryptanalytic efforts at
Bletchley Parkduring WWII spurred the development of more efficient means for carrying out repetitious tasks. de Bletchley Parkduring WWII spurred the development of more efficient means for carrying out repetitious tasks.
This culminated in the development of the de This culminated in the development of the
Colossus, the world’s first fully electronic, digital, de Colossus, the world’s first fully electronic, digital,
programmablecomputer, which assisted in the decryption of ciphers generated by the German Army’s de programmablecomputer, which assisted in the decryption of ciphers generated by the German Army’s
Lorenz SZ40/42machine. de Lorenz SZ40/42machine.
Extensive open academic research into cryptography is relatively recent; it began only in the mid-1970’s. de Extensive open academic research into cryptography is relatively recent; it began only in the mid-1970’s.
In recent times, IBM personnel designed the algorithm that became the Federal (i.e., US) de In recent times, IBM personnel designed the algorithm that became the Federal (i.e., US)
Data Encryption Standard; de Data Encryption Standard;
Whitfield Diffieand de Whitfield Diffieand
Martin Hellmanpublished de Martin Hellmanpublished
their key agreement algorithm; de their key agreement algorithm;
and the de and the
RSAalgorithm was published in de RSAalgorithm was published in
Martin Gardner‘s de Martin Gardner‘s
Scientific American column. de Scientific American column.
Following their work in 1976, it became popular to consider cryptography systems based on mathematical problems that are easy to state but have been found difficult to solve. de Following their work in 1976, it became popular to consider cryptography systems based on mathematical problems that are easy to state but have been found difficult to solve.
Since then, cryptography has become a widely used tool in communications, de Since then, cryptography has become a widely used tool in communications,
computer networks, and de computer networks, and
computer securitygenerally. de computer securitygenerally.
Some modern cryptographic techniques can only keep their keys secret if certain mathematical problems are de Some modern cryptographic techniques can only keep their keys secret if certain mathematical problems are
intractable, such as the de intractable, such as the
integer factorizationor the de integer factorizationor the
discrete logarithmproblems, so there are deep connections with de discrete logarithmproblems, so there are deep connections with
abstract mathematics. de abstract mathematics.
There are very few cryptosystems that are proven to be unconditionally secure. de There are very few cryptosystems that are proven to be unconditionally secure.
The de The
one-time padis one, and was proven to be so by Claude Shannon. de one-time padis one, and was proven to be so by Claude Shannon.
There are a few important algorithms that have been proven secure under certain assumptions. de There are a few important algorithms that have been proven secure under certain assumptions.
For example, the infeasibility of factoring extremely large integers is the basis for believing that de For example, the infeasibility of factoring extremely large integers is the basis for believing that
RSAis secure, and some other systems, but even so proof of unbreakability is unavailable since the underlying mathematical problem remains open. de RSAis secure, and some other systems, but even so proof of unbreakability is unavailable since the underlying mathematical problem remains open.
In practice, these are widely used, and are believed unbreakable in practice by most competent observers. de In practice, these are widely used, and are believed unbreakable in practice by most competent observers.
There are systems similar to RSA, such as one by de There are systems similar to RSA, such as one by
Michael O. Rabinthat are provably secure provided factoring de Michael O. Rabinthat are provably secure provided factoring
n = pqis impossible; it is quite unusable in practice. de n = pqis impossible; it is quite unusable in practice.
The de The
discrete logarithm problemis the basis for believing some other cryptosystems are secure, and again, there are related, less practical systems that are provably secure relative to the solvability or insolvability discrete log problem. de discrete logarithm problemis the basis for believing some other cryptosystems are secure, and again, there are related, less practical systems that are provably secure relative to the solvability or insolvability discrete log problem.
As well as being aware of cryptographic history, cryptographic algorithm and system designers must also sensibly consider probable future developments while working on their designs. de As well as being aware of cryptographic history, cryptographic algorithm and system designers must also sensibly consider probable future developments while working on their designs.
For instance, continuous improvements in computer processing power have increased the scope of de For instance, continuous improvements in computer processing power have increased the scope of
brute-force attacks, so when specifying de brute-force attacks, so when specifying
key lengths, the required key lengths are similarly advancing. de key lengths, the required key lengths are similarly advancing.
The potential effects of de The potential effects of
quantum computingare already being considered by some cryptographic system designers developing de quantum computingare already being considered by some cryptographic system designers developing
post-quantum cryptography; the announced imminence of small implementations of these machines may be making the need for preemptive caution rather more than merely speculative. [4] de post-quantum cryptography; the announced imminence of small implementations of these machines may be making the need for preemptive caution rather more than merely speculative. [4]
Symmetric-key cryptography de Symmetric-key cryptography
Main article:Symmetric-key algorithm de Main article:Symmetric-key algorithm
diagram showing encrypt with a key and decrypt process de diagram showing encrypt with a key and decrypt process
Symmetric-key cryptography, where a single key is used for encryption and decryption de Symmetric-key cryptography, where a single key is used for encryption and decryption
Symmetric-key cryptography refers to encryption methods in which both the sender and receiver share the same key (or, less commonly, in which their keys are different, but related in an easily computable way). de Symmetric-key cryptography refers to encryption methods in which both the sender and receiver share the same key (or, less commonly, in which their keys are different, but related in an easily computable way).
This was the only kind of encryption publicly known until June 1976. de This was the only kind of encryption publicly known until June 1976.
logic diagram showing International Data Encryption Algorithm cypher process de logic diagram showing International Data Encryption Algorithm cypher process
One round (out of 8.5) of theIDEAcipher, used in most versions ofPGPand OpenPGP compatible software for time-efficient encryption of messages de One round (out of 8.5) of theIDEAcipher, used in most versions ofPGPand OpenPGP compatible software for time-efficient encryption of messages
Symmetric key ciphers are implemented as either de Symmetric key ciphers are implemented as either
block ciphersor de block ciphersor
stream ciphers. de stream ciphers.
A block cipher enciphers input in blocks of plaintext as opposed to individual characters, the input form used by a stream cipher. de A block cipher enciphers input in blocks of plaintext as opposed to individual characters, the input form used by a stream cipher.
The de The
Data Encryption Standard(DES) and the de Data Encryption Standard(DES) and the
Advanced Encryption Standard(AES) are block cipher designs that have been designated de Advanced Encryption Standard(AES) are block cipher designs that have been designated
cryptography standardsby the US government (though DES’s designation was finally withdrawn after the AES was adopted). de cryptography standardsby the US government (though DES’s designation was finally withdrawn after the AES was adopted).
Despite its deprecation as an official standard, DES (especially its still-approved and much more secure de Despite its deprecation as an official standard, DES (especially its still-approved and much more secure
triple-DESvariant) remains quite popular; it is used across a wide range of applications, from ATM encryption de triple-DESvariant) remains quite popular; it is used across a wide range of applications, from ATM encryption
to de to
e-mail privacy de e-mail privacy
and de and
secure remote access. de secure remote access.
Many other block ciphers have been designed and released, with considerable variation in quality. de Many other block ciphers have been designed and released, with considerable variation in quality.
Many, even some designed by capable practitioners, have been thoroughly broken, such as de Many, even some designed by capable practitioners, have been thoroughly broken, such as
Stream ciphers, in contrast to the ‘block’ type, create an arbitrarily long stream of key material, which is combined with the plaintext bit-by-bit or character-by-character, somewhat like the de Stream ciphers, in contrast to the ‘block’ type, create an arbitrarily long stream of key material, which is combined with the plaintext bit-by-bit or character-by-character, somewhat like the
one-time pad. de one-time pad.
In a stream cipher, the output stream is created based on a hidden internal state that changes as the cipher operates. de In a stream cipher, the output stream is created based on a hidden internal state that changes as the cipher operates.
That internal state is initially set up using the secret key material. de That internal state is initially set up using the secret key material.
RC4is a widely used stream cipher; see de RC4is a widely used stream cipher; see
Block cipher modes of operation. de Block cipher modes of operation.
Cryptographic hash functionsare a third type of cryptographic algorithm. de Cryptographic hash functionsare a third type of cryptographic algorithm.
They take a message of any length as input, and output a short, fixed length de They take a message of any length as input, and output a short, fixed length
hash, which can be used in (for example) a digital signature. de hash, which can be used in (for example) a digital signature.
For good hash functions, an attacker cannot find two messages that produce the same hash. de For good hash functions, an attacker cannot find two messages that produce the same hash.
MD4is a long-used hash function that is now broken; de MD4is a long-used hash function that is now broken;
MD5, a strengthened variant of MD4, is also widely used but broken in practice. de MD5, a strengthened variant of MD4, is also widely used but broken in practice.
The US de The US
National Security Agencydeveloped the Secure Hash Algorithm series of MD5-like hash functions: SHA-0 was a flawed algorithm that the agency withdrew; de National Security Agencydeveloped the Secure Hash Algorithm series of MD5-like hash functions: SHA-0 was a flawed algorithm that the agency withdrew;
SHA-1is widely deployed and more secure than MD5, but cryptanalysts have identified attacks against it; the de SHA-1is widely deployed and more secure than MD5, but cryptanalysts have identified attacks against it; the
SHA-2family improves on SHA-1, but is vulnerable to clashes as of 2011; and the US standards authority thought it “prudent” from a security perspective to develop a new standard to “significantly improve the robustness of de SHA-2family improves on SHA-1, but is vulnerable to clashes as of 2011; and the US standards authority thought it “prudent” from a security perspective to develop a new standard to “significantly improve the robustness of
NIST‘s overall hash algorithm toolkit.” de NIST‘s overall hash algorithm toolkit.”
Thus, a de Thus, a
hash function design competitionwas meant to select a new U.S. national standard, to be called de hash function design competitionwas meant to select a new U.S. national standard, to be called
SHA-3, by 2012. de SHA-3, by 2012.
The competition ended on October 2, 2012 when the NIST announced that de The competition ended on October 2, 2012 when the NIST announced that
Keccakwould be the new SHA-3 hash algorithm. de Keccakwould be the new SHA-3 hash algorithm.
Unlike block and stream ciphers that are invertible, cryptographic hash functions produce a hashed output that cannot be used to retrieve the original input data. de Unlike block and stream ciphers that are invertible, cryptographic hash functions produce a hashed output that cannot be used to retrieve the original input data.
Cryptographic hash functions are used to verify the authenticity of data retrieved from an untrusted source or to add a layer of security. de Cryptographic hash functions are used to verify the authenticity of data retrieved from an untrusted source or to add a layer of security.
Modern cryptography de Modern cryptography
The modern field of cryptography can be divided into several areas of study. de The modern field of cryptography can be divided into several areas of study.
The chief ones are discussed here; see de The chief ones are discussed here; see
Topics in Cryptographyfor more. de Topics in Cryptographyfor more.
Public-key cryptography de Public-key cryptography
diagram of Public-key cryptography showing public key and private key de diagram of Public-key cryptography showing public key and private key
Public-key cryptography, where different keys are used for encryption and decryption. de Public-key cryptography, where different keys are used for encryption and decryption.
Symmetric-key cryptosystems use the same key for encryption and decryption of a message, although a message or group of messages can have a different key than others. de Symmetric-key cryptosystems use the same key for encryption and decryption of a message, although a message or group of messages can have a different key than others.
A significant disadvantage of symmetric ciphers is the de A significant disadvantage of symmetric ciphers is the
key managementnecessary to use them securely. de key managementnecessary to use them securely.
Each distinct pair of communicating parties must, ideally, share a different key, and perhaps for each ciphertext exchanged as well. de Each distinct pair of communicating parties must, ideally, share a different key, and perhaps for each ciphertext exchanged as well.
The number of keys required increases as the de The number of keys required increases as the
squareof the number of network members, which very quickly requires complex key management schemes to keep them all consistent and secret. de squareof the number of network members, which very quickly requires complex key management schemes to keep them all consistent and secret.
headshots of Whitfield Diffie and Martin Hellman de headshots of Whitfield Diffie and Martin Hellman
Facultatif de Facultatif

Other sentences

Original Similar TM records
https://en.wikipedia.org/wiki/Ancient_Greek_language
Ancient Greek: “hidden, secret”; and “to write”, or “study”, respectively [1] ) is the practice and study of techniques for
https://en.wikipedia.org/wiki/Cryptography#cite_note-1
https://en.wikipedia.org/wiki/Secure_communication
https://en.wikipedia.org/wiki/Adversary_(cryptography)
adversaries. [2] More generally, cryptography is about constructing and analyzing
https://en.wikipedia.org/wiki/Cryptography#cite_note-rivest90-2
https://en.wikipedia.org/wiki/Communications_protocol
protocolsthat prevent third parties or the public from reading private messages; [3] various aspects in
https://en.wikipedia.org/wiki/Cryptography#cite_note-modern-crypto-3
https://en.wikipedia.org/wiki/Information_security
https://en.wikipedia.org/wiki/Confidentiality
https://en.wikipedia.org/wiki/Data_integrity
https://en.wikipedia.org/wiki/Authentication
https://en.wikipedia.org/wiki/Non-repudiation
https://en.wikipedia.org/wiki/Cryptography#cite_note-hac-4
https://en.wikipedia.org/wiki/Mathematics
https://en.wikipedia.org/wiki/Computer_science
https://en.wikipedia.org/wiki/Electrical_engineering
https://en.wikipedia.org/wiki/Communication_science
https://en.wikipedia.org/wiki/Physics
https://en.wikipedia.org/wiki/Electronic_commerce
https://en.wikipedia.org/wiki/Credit_card_chip
https://en.wikipedia.org/wiki/Digital_currencies
https://en.wikipedia.org/wiki/Password
https://en.wikipedia.org/wiki/Military_communications
https://en.wikipedia.org/wiki/Encryption
encryption , the conversion of information from a readable state to apparent
https://en.wikipedia.org/wiki/Nonsense
https://en.wikipedia.org/wiki/Alice_and_Bob
often uses the namesAlice (“A”) for the sender, Bob (“B”) for the intended recipient, and Eve (“eavesdropper“) for the adversary. [5] Since the development of
https://en.wikipedia.org/wiki/Eavesdropper
https://en.wikipedia.org/wiki/Cryptography#cite_note-codesintro-5
https://en.wikipedia.org/wiki/Rotor_machine
https://en.wikipedia.org/wiki/World_War_I
https://en.wikipedia.org/wiki/Computer
https://en.wikipedia.org/wiki/World_War_II
https://en.wikipedia.org/wiki/Algorithm
https://en.wikipedia.org/wiki/Computational_hardness_assumption
https://en.wikipedia.org/wiki/Integer_factorization
https://en.wikipedia.org/wiki/Information_theoretic_security
https://en.wikipedia.org/wiki/One-time_pad
https://en.wikipedia.org/wiki/Espionage
https://en.wikipedia.org/wiki/Sedition
seditionhas led many governments to classify it as a weapon and to limit or even prohibit its use and export. [6] In some jurisdictions where the use of cryptography is legal, laws permit investigators to
https://en.wikipedia.org/wiki/Cryptography#cite_note-cryptolaw-6
https://en.wikipedia.org/wiki/Key_disclosure_law
compel the disclosureof encryption keys for documents relevant to an investigation. [7] [8] Cryptography also plays a major role in
https://en.wikipedia.org/wiki/Cryptography#cite_note-UK_law-7
https://en.wikipedia.org/wiki/Cryptography#cite_note-RangerSteve1-8
https://en.wikipedia.org/wiki/Digital_rights_management
https://en.wikipedia.org/wiki/Copyright_infringement
copyright infringementof digital media. [9]
https://en.wikipedia.org/wiki/Cryptography#cite_note-AACS-9
The first use of the termcryptograph(as opposed tocryptogram) dates back to the 19th century—originating from The Gold-Bug , a novel byEdgar Allan Poe.
https://en.wikipedia.org/wiki/The_Gold-Bug
https://en.wikipedia.org/wiki/Edgar_Allan_Poe
https://en.wikipedia.org/wiki/Cryptography#cite_note-10
10
https://en.wikipedia.org/wiki/Plaintext
https://en.wikipedia.org/wiki/Ciphertext
https://en.wikipedia.org/wiki/Cryptography#cite_note-kahnbook-11
11
https://en.wikipedia.org/wiki/Cipher
cipher (or
https://en.wikipedia.org/wiki/Key_(cryptography)
https://en.wikipedia.org/wiki/Cryptosystem
https://en.wikipedia.org/wiki/Authentication
https://en.wikipedia.org/wiki/Symmetric-key_algorithm
https://en.wikipedia.org/wiki/Public-key_cryptography
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12
https://en.wikipedia.org/wiki/Rivest-Shamir-Adleman
https://en.wikipedia.org/wiki/Elliptic_Curve_Cryptography
https://en.wikipedia.org/wiki/Advanced_Encryption_Standard
https://en.wikipedia.org/wiki/Data_Encryption_Standard
https://en.wikipedia.org/wiki/Cryptography#cite_note-13
13
https://en.wikipedia.org/wiki/Colloquial
https://en.wikipedia.org/wiki/Code_(cryptography)
https://en.wikipedia.org/wiki/Code_word
https://en.wikipedia.org/wiki/Cryptanalysis
https://en.wikipedia.org/wiki/Cryptography#cite_note-goldreichbook-14
14
https://en.wikipedia.org/wiki/Cryptography#cite_note-websters-15
15
https://en.wikipedia.org/wiki/Request_for_Comments_(identifier)
https://tools.ietf.org/html/rfc2828
https://en.wikipedia.org/wiki/Steganography
https://en.wikipedia.org/wiki/Cryptography#cite_note-16
16
https://en.wikipedia.org/wiki/Information
https://en.wikipedia.org/wiki/Secrecy
https://en.wikipedia.org/wiki/Communications
https://en.wikipedia.org/wiki/Spy
https://en.wikipedia.org/wiki/Diplomat
https://en.wikipedia.org/wiki/Authentication
https://en.wikipedia.org/wiki/Digital_signature
https://en.wikipedia.org/wiki/Interactive_proof_system
https://en.wikipedia.org/wiki/Secure_multiparty_computation
https://en.wikipedia.org/wiki/Language
https://en.wikipedia.org/wiki/Lexicographic_code
https://en.wikipedia.org/wiki/Information_theory
https://en.wikipedia.org/wiki/Computational_complexity_theory
https://en.wikipedia.org/wiki/Statistics
https://en.wikipedia.org/wiki/Combinatorics
https://en.wikipedia.org/wiki/Abstract_algebra
https://en.wikipedia.org/wiki/Number_theory
https://en.wikipedia.org/wiki/Engineering
https://en.wikipedia.org/wiki/Security_engineering
https://en.wikipedia.org/wiki/Quantum_physics
https://en.wikipedia.org/wiki/Quantum_cryptography
https://en.wikipedia.org/wiki/Quantum_computer
https://en.wikipedia.org/wiki/Binary_numeral_system
https://en.wikipedia.org/wiki/Bit
https://en.wikipedia.org/wiki/Cryptanalysis
https://en.wikipedia.org/wiki/Bletchley_Park
https://en.wikipedia.org/wiki/Colossus_computer
https://en.wikipedia.org/wiki/Computer_programming
https://en.wikipedia.org/wiki/Lorenz_SZ40/42
https://en.wikipedia.org/wiki/Data_Encryption_Standard
https://en.wikipedia.org/wiki/Whitfield_Diffie
https://en.wikipedia.org/wiki/Martin_Hellman
https://en.wikipedia.org/wiki/Diffie-Hellman
https://en.wikipedia.org/wiki/Cryptography#cite_note-dh2-30
30
https://en.wikipedia.org/wiki/RSA_(algorithm)
https://en.wikipedia.org/wiki/Martin_Gardner
https://en.wikipedia.org/wiki/Scientific_American
https://en.wikipedia.org/wiki/Cryptography#cite_note-31
31
https://en.wikipedia.org/wiki/Computer_network
https://en.wikipedia.org/wiki/Computer_security
https://en.wikipedia.org/wiki/Computational_complexity_theory#Intractability
https://en.wikipedia.org/wiki/Integer_factorization
https://en.wikipedia.org/wiki/Discrete_logarithm
https://en.wikipedia.org/wiki/Abstract_mathematics
https://en.wikipedia.org/wiki/One-time_pad
https://en.wikipedia.org/wiki/RSA_(cryptosystem)
https://en.wikipedia.org/wiki/Michael_O._Rabin
https://en.wikipedia.org/wiki/Discrete_logarithm_problem
https://en.wikipedia.org/wiki/Cryptography#cite_note-32
32
https://en.wikipedia.org/wiki/Brute-force_attack
https://en.wikipedia.org/wiki/Key_length
https://en.wikipedia.org/wiki/Cryptography#cite_note-fortify-33
33
https://en.wikipedia.org/wiki/Quantum_computing
https://en.wikipedia.org/wiki/Post-quantum_cryptography
https://en.wikipedia.org/wiki/Cryptography#cite_note-hac-4
https://en.wikipedia.org/wiki/Symmetric-key_algorithm
https://en.wikipedia.org/wiki/File:Symmetric_key_encryption.svg
https://upload.wikimedia.org/wikipedia/commons/thumb/2/27/Symmetric_key_encryption.svg/250px-Symmetric_key_encryption.svg.png
https://en.wikipedia.org/wiki/Cryptography#cite_note-dh2-30
30
https://en.wikipedia.org/wiki/File:International_Data_Encryption_Algorithm_InfoBox_Diagram.svg
https://upload.wikimedia.org/wikipedia/commons/thumb/a/af/International_Data_Encryption_Algorithm_InfoBox_Diagram.svg/220px-International_Data_Encryption_Algorithm_InfoBox_Diagram.svg.png
https://en.wikipedia.org/wiki/International_Data_Encryption_Algorithm
https://en.wikipedia.org/wiki/Pretty_Good_Privacy
https://en.wikipedia.org/wiki/Block_ciphers
https://en.wikipedia.org/wiki/Stream_ciphers
https://en.wikipedia.org/wiki/Data_Encryption_Standard
https://en.wikipedia.org/wiki/Advanced_Encryption_Standard
https://en.wikipedia.org/wiki/Cryptography_standards
https://en.wikipedia.org/wiki/Cryptography#cite_note-aes-34
34
https://en.wikipedia.org/wiki/Triple-DES
https://en.wikipedia.org/wiki/Cryptography#cite_note-atm-35
35
https://en.wikipedia.org/wiki/E-mail_privacy
https://en.wikipedia.org/wiki/Cryptography#cite_note-opgp-36
36
https://en.wikipedia.org/wiki/Secure_Shell
https://en.wikipedia.org/wiki/Cryptography#cite_note-ssh-37
37
https://en.wikipedia.org/wiki/FEAL
FEAL. [4]
https://en.wikipedia.org/wiki/Cryptography#cite_note-hac-4
https://en.wikipedia.org/wiki/Cryptography#cite_note-schneierbook-38
38
https://en.wikipedia.org/wiki/One-time_pad
https://en.wikipedia.org/wiki/RC4
https://en.wikipedia.org/wiki/Category:Stream_ciphers
Category:Stream ciphers. [4] Block ciphers can be used as stream ciphers; see
https://en.wikipedia.org/wiki/Cryptography#cite_note-hac-4
https://en.wikipedia.org/wiki/Block_cipher_modes_of_operation
https://en.wikipedia.org/wiki/Cryptographic_hash_functions
https://en.wikipedia.org/wiki/Hash_function
https://en.wikipedia.org/wiki/MD4
https://en.wikipedia.org/wiki/MD5
https://en.wikipedia.org/wiki/National_Security_Agency
https://en.wikipedia.org/wiki/SHA-1
https://en.wikipedia.org/wiki/SHA-2
https://en.wikipedia.org/wiki/National_Institute_of_Standards_and_Technology
https://en.wikipedia.org/wiki/Cryptography#cite_note-39
39
https://en.wikipedia.org/wiki/NIST_hash_function_competition
https://en.wikipedia.org/wiki/SHA-3
https://en.wikipedia.org/wiki/Keccak
https://en.wikipedia.org/wiki/Cryptography#cite_note-40
40
https://en.wikipedia.org/wiki/Message_authentication_code
Message authentication codes(MACs) are much like cryptographic hash functions, except that a secret key can be used to authenticate the hash value upon receipt; [4] this additional complication blocks an attack scheme against baredigest algorithms, and so has been thought worth the effort.
https://en.wikipedia.org/wiki/Cryptography#cite_note-hac-4
https://en.wikipedia.org/wiki/Md5
https://en.wikipedia.org/wiki/Topics_in_Cryptography
https://en.wikipedia.org/wiki/File:Public_key_encryption.svg
https://upload.wikimedia.org/wikipedia/commons/thumb/f/f9/Public_key_encryption.svg/250px-Public_key_encryption.svg.png
https://en.wikipedia.org/wiki/Key_management
https://en.wikipedia.org/wiki/Square_(algebra)
https://en.wikipedia.org/wiki/File:Diffie_and_Hellman.jpg
https://upload.wikimedia.org/wikipedia/commons/thumb/8/88/Diffie_and_Hellman.jpg/220px-Diffie_and_Hellman.jpg