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单词 cryptography
释义
cryptography

Mathematics
  • The area of mathematics concerning the secure scrambling of a message or information so that, if intercepted, the original message is, in practice, irretrievable without knowledge of the key. The original message is called the plaintext, and the scrambled message is called the ciphertext or cryptogram. The process of scrambling is called encryption and is achieved via a private or public key. The security of the encryption often relies on the prime factorization of very large numbers or a similar one-way function. See frequency analysis, RSA.


Computer
  • The coding of messages so as to render them unintelligible to other than authorized recipients. Many techniques are known for the conversion of the original message, known as plaintext, into its encrypted form, known as ciphertext, cipher, or code.

    In a simple cipher system, for example, the sender and recipient hold identical copies of a secret key, and also an algorithm with which they each generate identical pseudorandom bit sequences. During encryption the sender modifies the plaintext string by combining it with the pseudorandom sequence to produce the ciphertext; the ciphertext is then transmitted. The recipient performs the reverse process with an identical pseudorandom sequence and the received ciphertext to recover the plaintext.

    An alternative technique is to use a block cipher, in which the ciphertext corresponding to each block of, typically, 64 bits of plaintext is generated algorithmically using a key. In a symmetric block cipher the key used for decryption is closely related to that used for encryption, and both have to be kept secret. With asymmetric or public key encryption, the decryption key cannot be deduced from knowledge of the encryption key, which can thus be publicized to all intending message senders. See Data Encryption Standard, RSA encryption.


Internet
  • Cryptography employs methods that transform a message containing sensitive data into one that cannot be read by someone who is not authorized to access it. To do this, the text to be sent is transformed using a set of rules known as a cipher. The rules in the cipher will be varied according to a key which is provided by the sender of the text. The process of modifying text using a cipher is known as encryption. Once a text has been encrypted it is sent over a transmission line and decoded by its recipient who uses a key to transform the text back to its original form. This is a process known as decryption.


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