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Re: GRUB and boot partition

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On 01/03/18 06:45, Gary Dale wrote:
> On 2018-01-02 02:35 PM, Pascal Hambourg wrote:
>>
>> Encryption does not require extra space (except for header and 
>> block padding). Encrypted data have the same size of cleartext data.

+1


> Encryption is similar in concept to compression. 

AFAIK common use on Debian systems:

1.  Encryption functions [1] are reversible functions that transform 
data 1:1 in size, and are lossless.

2.  Compression functions [2] are reversible functions that strive for 
size ratios of N:1, where N > 1 (uncompressed:compressed), and can be 
lossless or lossly.


A related topic is hashing functions [3] (N:fixed, can be difficult to 
reverse).


> It could even reduce the space requirements.

I'm curious -- can you cite a compressing cipher code that cannot be 
reduced to independent compression and cipher functions?


> Encryption and compression both work by replacing strings of letters with something else.

I agree that encryption and compression are both forms of coding [4].


> Encryption and compression both work by replacing strings of letters 
> with something else. What we call clear text, for example, is just a  > Caesar cipher where each letter is replaced by a number (its ASCII code
> or unicode). 

ASCII [5] is a transliteration code -- replace a token from one alphabet 
(Roman letters, Arabic numerals, common English symbols, etc.) with a 
token from another alphabet (7-bit binary number).  Spelling, grammar, 
and meaning are unchanged.


The goal of a substitution cipher is to conceal meaning, and can be done 
without changing alphabets (e.g. rot13 [6]).  Spelling and grammar are 
unchanged (which facilitates cryptanalysis).


> Morse code, on the other hand, replaces common letters with 
> shorter sequences of dots and dashes than less common letters.

I agree that Morse Code [7] uses frequency-based techniques.


David


References:

[1] https://en.wikipedia.org/wiki/Encryption

[2] https://en.wikipedia.org/wiki/Data_compression

[3] https://en.wikipedia.org/wiki/Hash_function

[4] https://en.wikipedia.org/wiki/Code

[5] https://en.wikipedia.org/wiki/ASCII

[6] https://en.wikipedia.org/wiki/ROT13

[7] https://en.wikipedia.org/wiki/Morse_code

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Re: GRUB and boot partition Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-01-02 20:40 +0100
  Re: GRUB and boot partition Gary Dale <garydale@torfree.net> - 2018-01-03 15:50 +0100
    Re: GRUB and boot partition David Christensen <dpchrist@holgerdanske.com> - 2018-01-03 20:10 +0100
      Re: GRUB and boot partition Gary Dale <garydale@torfree.net> - 2018-01-05 16:30 +0100
        Re: GRUB and boot partition Richard Hector <richard@walnut.gen.nz> - 2018-01-06 13:10 +0100

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