> 1. When a passphrase is used a key in symetric cryptography, how does
> the pass phrase map to the key in an algorithm like AES?
The recommended way to generate keys from passwords is to use PBKDF2
function (see wikipedia).
> ie....how
> many letters correspond to 1 bit? etc?
The "value" of one letter depends on the size of the set, where the
characters are chosen from.
Say, if you only use lower case letters, then the size of the set is
26. Taking a logarithm base 2 of 26 is
bc -l
bc 1.06Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.
l(26)/l(2)
4.70043971814109216044
one letter is around 4.7 bits.
if you have lower-case letters, capital letters, numbers and 32
possible other special characters `~!@#$%^&*()-_=+\|]}[{'";:/?.>,<
then you'll have
> the pass phrase map to the key in an algorithm like AES?
The recommended way to generate keys from passwords is to use PBKDF2
function (see wikipedia).
> ie....how
> many letters correspond to 1 bit? etc?
The "value" of one letter depends on the size of the set, where the
characters are chosen from.
Say, if you only use lower case letters, then the size of the set is
26. Taking a logarithm base 2 of 26 is
bc -l
bc 1.06Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.
l(26)/l(2)
4.70043971814109216044
one letter is around 4.7 bits.
if you have lower-case letters, capital letters, numbers and 32
possible other special characters `~!@#$%^&*()-_=+\|]}[{'";:/?.>,<
then you'll have
l(26+26+10+32)/l(2)
6.55458885167763737222
around 6.55 bits per character.
--
Vladimir Ivanov
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