暗号化

Encryption — Grokipedia Fact-checked by Grok 3 months ago Encryption Ara Eve Leo Sal 1x Encryption is the cryptographic transformation of data, known as plaintext , into an unintelligible form called ciphertext , using mathematical algorithms and secret keys to prevent unauthorized access or disclosure. [1] This process ensures confidentiality by rendering information unreadable without the corresponding decryption key, forming the core mechanism of modern cryptography for protecting sensitive communications, financial transactions, and stored data. [2] Originating from ancient practices such as substitution ciphers used by civilizations like the Egyptians and Spartans around 1900 BC and 400 BC respectively, encryption evolved through military applications in wartime code-breaking to contemporary digital standards driven by computational advances. [3] Key milestones include the development of symmetric algorithms like the Data Encryption Standard (DES) in the 1970s and the Advanced Encryption Standard (AES) in 2001, which provide efficient bulk data protection using a single shared key for both encryption and decryption. [4] Asymmetric encryption, introduced in the 1970s with concepts like public-key systems, enables secure key exchange over insecure channels by employing distinct public keys for encryption and private keys for decryption, underpinning protocols such as secure sockets layer (SSL) and its successor transport layer security (TLS). [5] Encryption's defining role in safeguarding privacy has sparked ongoing controversies, particularly tensions between individual rights and governmental imperatives for national security , with proposals for mandated backdoors or weakened standards criticized for undermining overall system integrity and enabling broader vulnerabilities. [6] Empirical evidence from cryptographic research underscores that introducing deliberate weaknesses, as advocated in some policy debates, risks exploitation by adversaries far beyond intended law enforcement access, prioritizing causal realism in assessing real-world threats over unsubstantiated assurances of controlled implementation. [7] Despite such debates, robust encryption remains indispensable for economic and societal functions, with standards like AES demonstrating resilience against known attacks through rigorous peer-reviewed validation. [4] History Ancient and Classical Cryptography The scytale , a transposition cipher device, was used by Spartan military forces in the 5th century BCE to secure messages during campaigns such as the Peloponnesian War . [8] A narrow strip of leather or parchment was wrapped spirally around a wooden cylinder of fixed diameter, with the plaintext inscribed longitudinally across the turns; unwrapping the strip produced a scrambled sequence of characters, which could only be reordered correctly using an identical cylinder. [9] Ancient accounts, including those preserved by Plutarch , attest to its role in authenticating and protecting orders among separated commanders, emphasizing shared physical tools over algorithmic secrecy. [9] In Greek antiquity, substitution and coding schemes supplemented transposition methods, as seen in the Polybius square attributed to the historian Polybius (c. 200–118 BCE). [10] This 5x5 grid assigned each letter (excluding one for the Greek alphabet's 24 characters) to row-column coordinates, enabling concise signaling via torches or adaptable encryption by replacing letters with numeric pairs; Polybius detailed its use for rapid, distant communication in his Histories , though direct cryptographic applications relied on manual transcription. [10] Such systems prioritized brevity and error resistance in visual or verbal transmission over resistance to interception, reflecting the era's focus on military expediency. [11] Roman adaptations emphasized monoalphabetic substitution, exemplified by the Caesar cipher employed by Julius Caesar circa 50 BCE during the Gallic Wars . [12] Letters were shifted by a fixed value—typically three positions in the Latin alphabet (e.g., A to D, B to E)—to encode sensitive dispatches, as recorded by Suetonius in The Twelve Caesars . [13] This method protected military and personal correspondence from casual readers but remained vulnerable to exhaustive trial or pattern recognition due to its simplicity and lack of variability. [12] Overall, ancient and classical cryptography was constrained by manual execution, low message volumes, and dependence on trusted couriers, rendering it suitable primarily for tactical secrecy rather than widespread or long-term protection. [13] Medieval to Early Modern Developments In the 9th century , Arab scholars advanced cryptanalysis significantly, with Al-Kindi (c. 801–873 CE) authoring the first known treatise on the subject, Risāla fī fī khabar taʾwīl al-rumūz ( Manuscript on Deciphering Cryptographic Messages), which introduced frequency analysis as a method to break monoalphabetic substitution ciphers by comparing letter frequencies in ciphertext to those in the target language, such as Arabic derived from Quranic texts. [14] [15] This technique exploited the statistical regularity of languages, where common letters like alif or lam in Arabic appeared predictably, enabling systematic decryption without keys and rendering simple substitution ciphers vulnerable. [16] Subsequent Arab cryptologists, building on Al-Kindi , developed homophonic substitutions—using multiple symbols for frequent letters—to obscure frequencies, reflecting a response to growing diplomatic and military espionage needs in the expanding Islamic caliphates. [17] Knowledge of these methods transmitted to Europe via translations and trade routes during the late medieval period, influencing cryptologic practices amid the Renaissance's revival of classical learning and intensification of interstate rivalries, particularly in Italian city-states like Venice and Florence , where encrypted diplomatic dispatches became routine for protecting trade secrets and alliances. [18] By the mid-15th century, Leon Battista Alberti (1404–1472), in his treatise De componendis cifris (c. 1467), described the first polyalphabetic cipher device: a rotating disk system with two concentric alphabets—one fixed (stabilis) and one movable (mobilis)—allowing the encipherer to shift the inner disk periodically via an index letter, thus using multiple substitution alphabets to flatten letter frequencies and resist frequency analysis . [19] [20] Alberti's innovation incorporated mixed alphabets (rearranging letters and adding numerals or nulls) and variable periods, marking a shift from ad hoc substitutions to mechanical aids for more secure, systematic encryption suited to papal and secular correspondence. [21] In the 16th century , French diplomat Blaise de Vigenère (1523–1596) further refined polyalphabetic systems in Traicté des chiffres (1586), presenting a tableau (grid) of 26 Caesar-shifted alphabets for keyword-based encryption, where the plaintext letter is combined with successive key letters via modular addition (e.g., A=0 to Z=25), producing ciphertext that cycles through alphabets and resists monoalphabetic attacks unless the key length is guessed. [22] [23] Though anticipated by earlier Italians like Bellaso (1553), Vigenère's tableau emphasized practical tabula recta implementation and autokey variants (using prior plaintext as key extension), enhancing usability for military and courtly espionage during Europe's religious wars and colonial expansions. [18] These developments transitioned cryptography from empirical, language-specific tools to principled, device-assisted methods, driven by the causal demands of proliferating secret communications in an era of fragmented polities and intelligence rivalries, yet still vulnerable to emerging statistical attacks on short keys. [24] 19th and Early 20th Century Advances The Playfair cipher , invented in 1854 by Charles Wheatstone and promoted by Lord Playfair, introduced digraph substitution using a 5×5 polybius square to encrypt pairs of letters, offering resistance to frequency analysis superior to simple substitution ciphers. [25] This manual system gained adoption in British diplomatic and military communications, including during the Second Boer War (1899–1902) and World War I , where it secured field messages against interception. [26] The expansion of telegraph networks in the late 19th century heightened demands for secure long-distance transmission, spurring codebooks and polyalphabetic adaptations like the Vigenère cipher for electrical signaling, though vulnerabilities to crib-based attacks persisted. [27] By 1917, AT&T engineer Gilbert Vernam devised an automated stream cipher for teleprinters, employing a perforated tape of random characters added modulo 26 to plaintext , which functioned as a practical precursor to the one-time pad when keys were non-repeating. [28] Patented in 1919 (U.S. Patent 1,310,719), Vernam's system enabled synchronous encryption-decryption over wires, addressing synchronization challenges in early electrical cryptosystems. [29] Electromechanical innovations accelerated in the 1910s–1920s with rotor machines, as German engineer Arthur Scherbius filed a patent on February 23, 1918, for a device using rotating wired cylinders to generate dynamic substitutions, commercialized by Chiffriermaschinen-Aktiengesellschaft in the early 1920s. [30] These precursors to more advanced wartime rotors provided commercial and governmental users with machine-assisted polyalphabetic encryption, leveraging industrialization's mechanical precision for radio and telegraph security amid rising international espionage . [31] Concurrently, cryptology professionalized through specialized military bureaus and scientific methodologies, as seen in U.S. Signal Corps efforts from 1900 onward to systematize code recovery amid telegraph proliferation. [32] World War II and Postwar Era The Germa