Block, SkipCaptcha, Upload, Automoderated users, Check users, delete, edit, Moderators, move, oversight, protect, rollback
19,323
edits
Changes
Jump to navigation
Jump to search
mLine 7:
Line 7: − − The main problem is the "man in the middle attack". Instead of merely eavesdropping, an attacker would place himself between the 2 parties trying to communicate, and he would participate in the key exchange. The spy would agree on one key with the first party, agree on another key with the second party. Then he is able to decrypt (and re-encrypt and retransmit) the data sent over the channel. − − However the protocol is useful because it raises the difficulty of eavesdropping. A spy would have to be able to place himself "in between" the two parties he intends to spy on. Also, the spy needs to actively participate in the conversation in order to be able to spy. If he were to put a listening device on the cable, for example, he would not be able to understand the messages sent. Line 33:
Line 29: + + + +
→Diffie-Hellman key exchange protocol: better order
==Diffie-Hellman key exchange protocol==
==Diffie-Hellman key exchange protocol==
This is a method to secure a channel from eavesdroppers, by agreeing on an encryption key. It is used to let 2 parties agree on a key to be used for encrypting their communications, without actually transmitting said key on the channel between them. If somebody is eavesdropping he will not be able to deduce the key agreed upon from listening to the data.
This is a method to secure a channel from eavesdroppers, by agreeing on an encryption key. It is used to let 2 parties agree on a key to be used for encrypting their communications, without actually transmitting said key on the channel between them. If somebody is eavesdropping he will not be able to deduce the key agreed upon from listening to the data.
"Diffie-Hellman key exchange", relies on the fundamental [[hardness|difficulty]] of [[computing]] the discrete logarithm of a number in the [[Group (mathematics)|group]] ''G''. It was invented by [[Whitfield Diffie]] and Martin Hellman in 1976. The protocol proceeds in three steps:
"Diffie-Hellman key exchange", relies on the fundamental [[hardness|difficulty]] of [[computing]] the discrete logarithm of a number in the [[Group (mathematics)|group]] ''G''. It was invented by [[Whitfield Diffie]] and Martin Hellman in 1976. The protocol proceeds in three steps:
By increasing p, the procedure of looking for a can be made arbitrarily difficult. These days p is generally chosen to be "relatively large", meaning that it should require "a bit less" than 256 bits to represent. Determining a would take on average 2<sup>255</sup> steps (although some algorithms can do it in slightly less steps) to determine a.
By increasing p, the procedure of looking for a can be made arbitrarily difficult. These days p is generally chosen to be "relatively large", meaning that it should require "a bit less" than 256 bits to represent. Determining a would take on average 2<sup>255</sup> steps (although some algorithms can do it in slightly less steps) to determine a.
The main problem is the "man in the middle attack". Instead of merely eavesdropping, an attacker would place himself between the 2 parties trying to communicate, and he would participate in the key exchange. The spy would agree on one key with the first party, agree on another key with the second party. Then he is able to decrypt (and re-encrypt and retransmit) the data sent over the channel.
However the protocol is useful because it raises the difficulty of eavesdropping. A spy would have to be able to place himself "in between" the two parties he intends to spy on. Also, the spy needs to actively participate in the conversation in order to be able to spy. If he were to put a listening device on the cable, for example, he would not be able to understand the messages sent.
==RSA encryption==
==RSA encryption==