| Chosen Plaintext Attack |
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This appears, at first glance, to be an unrealistic model; it would certainly be unlikely that an attacker could persuade a human cryptographer to encrypt large amounts of plaintexts of the attacker's choosing. Modern cryptography, on the other hand, is implemented in software or hardware and is used for a diverse range of applications; for many cases, a chosen-plaintext attack is often very feasible. Chosen-plaintext attacks become extremely important in the context of Public Key Cryptography , where the encryption key is public and attackers can encrypt any plaintext they choose. Any cipher that can prevent chosen-plaintext attacks is then also guaranteed to be secure against Known-plaintext and ciphertext-only attacks; this is a conservative approach to security. Two forms of chosen-plaintext attack can be distinguished:
Non-randomized (deterministic) Public Key Encryption Algorithms are vulnerable to simple "dictionary"-type attacks, where the attacker builds a table of likely messages and their corresponding ciphertexts. To find the decryption of some observed ciphertext, the attacker simply looks the ciphertext up in the table. As a result, public-key definitions of security under chosen-plaintext attack require Probabilistic Encryption (i.e., randomized encryption). Conventional Symmetric Ciphers , in which the same key is used to encrypt and decrypt a text, may also be vulnerable to other forms of chosen-plaintext attack, for example, Differential Cryptanalysis of Block Cipher s. A technique termed '' Gardening '' was used by Allied codebreakers in World War II who were solving messages encrypted on the Enigma Machine . Gardening can be viewed as a chosen-plaintext attack. SEE ALSO |
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