Encryption involves applying an operation (an algorithm) to the data to be encrypted using the
private key to make them unintelligible. The slightest algorithm (such as an exclusive OR) can
make the system nearly tamper proof (there being so such thing as absolute security).
However, in the 1940s, Claude Shannon proved that to be completely secure, private-key
systems need to use keys that are at least as long as the message to be encrypted. Moreover,
symmetric encryption requires that a secure channel be used to exchange the key, which
seriously diminishes the usefulness of this kind of encryption system.
The main disadvantage of a secret-key cryptosystem is related to the exchange of keys.
Symmetric encryption is based on the exchange of a secret (keys). The problem of key
distribution therefore arises:
Moreover, a user wanting to communicate with several people while ensuring separate
confidentiality levels has to use as many private keys as there are people. For a group of N
people using a secret-key cryptosystem, it is necessary to distribute a number of keys equal to N
* (N-1) / 2.
In the 1920s, Gilbert Vernam and Joseph Mauborgne developed the One-Time Pad method
(sometimes called "One-Time Password" and abbreviated OTP), based on a randomly
generated private key that is used only once and is then destroyed. During the same period, the
Kremlin and the White House were connected by the famous red telephone, that is, a telephone
where calls were encrypted thanks to a private key according to the one-time pad method. The
private key was exchanged thanks to the diplomatic bag (playing the role of secure channel).
Encryption involves applying an operation (an algorithm) to the data to be encrypted using theprivate key to make them unintelligible. The slightest algorithm (such as an exclusive OR) canmake the system nearly tamper proof (there being so such thing as absolute security).However, in the 1940s, Claude Shannon proved that to be completely secure, private-keysystems need to use keys that are at least as long as the message to be encrypted. Moreover,symmetric encryption requires that a secure channel be used to exchange the key, whichseriously diminishes the usefulness of this kind of encryption system.The main disadvantage of a secret-key cryptosystem is related to the exchange of keys.Symmetric encryption is based on the exchange of a secret (keys). The problem of keydistribution therefore arises:Moreover, a user wanting to communicate with several people while ensuring separateconfidentiality levels has to use as many private keys as there are people. For a group of Npeople using a secret-key cryptosystem, it is necessary to distribute a number of keys equal to N* (N-1) / 2.In the 1920s, Gilbert Vernam and Joseph Mauborgne developed the One-Time Pad method(sometimes called "One-Time Password" and abbreviated OTP), based on a randomlygenerated private key that is used only once and is then destroyed. During the same period, theKremlin and the White House were connected by the famous red telephone, that is, a telephonewhere calls were encrypted thanks to a private key according to the one-time pad method. Theprivate key was exchanged thanks to the diplomatic bag (playing the role of secure channel).
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