Re:The strange story of “Extended Random”
by marshray on Sunday December 24, 2017 @12:45AM
(#15998187)
> If some of the plaintext bits are known, in theory the unpredictability should decrease. For an extreme example: if all 128 bits of plaintext are known, and all 128 bits of ciphertext are also known, there should be a single 128 bit AES key that maps that input to that output, so the entropy left in the key would be zero.
This is correct if either:
1. the planet held enough energy to perform a brute-force attack on a 128-bit key (it doesn't: https://en.wikipedia.org/wiki/Landauer%27s_principle ) and such an attack could be performed while the protected information was still relevant. Or:
2. You have an algorithmic break on AES that allows the attack to be carried massively more efficiently, enough to make it practical.
Cryptographers refer to this situation as 'winning'.
This is correct if either:
1. the planet held enough energy to perform a brute-force attack on a 128-bit key (it doesn't: https://en.wikipedia.org/wiki/Landauer%27s_principle ) and such an attack could be performed while the protected information was still relevant. Or:
2. You have an algorithmic break on AES that allows the attack to be carried massively more efficiently, enough to make it practical.
Cryptographers refer to this situation as 'winning'.