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Entropy strikes back! | 244 comments | Create New Account
Comments belong to whoever posts them. Please notify us of inappropriate comments.
Entropy strikes back!
Authored by: Anonymous on Tuesday, May 21 2013 @ 11:04 PM EDT
My apologies sir but I do believe you are confused about certain terms.
"Salt" in cryptography is not used to increase entropy (for it is
generally left unhashed/encrypted and actually doesn't increase entropy at all)
but instead it is used to prevent rainbow tables (tables of pre-computed hashes
to compare passwords to) from being effective as it increases their size
immensely (attempting to make the space/speed tradeoff tilted very far away from
space).

I am slightly confused by your explanation of entropy, but I think it is also
misinformed. Entropy is the number of ways a system can be arranged, that is to
say if I have a 8 character all lower case system, there are 26^8 ways it can be
arranged, or the system has an entropy of 26^8. While if I have 9 lowercase
characters, there are 26^9 ways they can be arranged. Any compression algorithm,
should either leave entropy alone (lossless algorithms, for example getting rid
of that 8th bit in ascii doesn't hurt anything but makes it smaller), or should
create less entropy (lossy algorithms, where you just assume certain results are
less likely to exist, and therefore don't, or it is an unimportant distinction
(who cares if the pixel is 1 degree blue-er)).

Also do remember, that an image format, if done carefully, could make any
message of the correct size, a 'sensible' answer (if it's just noise, oh well).
After all, all an image is is 5 or so numbers per pixel specifying their red
green blue colors brightness and transparency values, usually compressed in some
(lossy) way. So you can interpret any binary of the right size, as an image.

[ Reply to This | Parent | # ]

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