Single File System: Virtual File System Delphi Library
for Archive / Backup with Transparent Compression and Strong Encryption


Compression and encryption algorithms

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Compression algorithms
Single File System (SFS) provides 3 main compression algorithms:
·ZLIB algorithm (InfoZip, http://www.info-zip.org/)  
·BZIP algorithm (by Julian Seward, jseward@acm.org.)  
·PPM algorithm, variant G (by Dmitry Shkarin, shkarin@arstel.ru)  

SFS has 3 levels for each of above algorithms: Fastest, Normal and Max.

Level    Meaning    
sfsNone    No compression   
zlibFastest   ZLib algorithm, Fastest compression
   
zlibNormal   ZLib algorithm, Normal balance between speed and compression rate   
zlibMax    ZLib algorithm, Maximum compression, rather slow speed   
ppmFastest   PPM algorithm, Fastest compression
   
ppmNormal   PPM algorithm, Normal balance between speed and compression rate   
ppmMax    PPM algorithm, Maximum compression, rather slow speed   
bzipFastest   BZIP algorithm, Fastest compression
   
bzipNormal   BZIP algorithm, Normal balance between speed and compression rate   
bzipMax   BZIP algorithm, Maximum compression, rather slow speed   

Typically ZLib is the fastest algorithm, BZIP is fast and has a good rate, PPM provides the maximum rate with rather low speed.
But it also depends on compression level: i.e. for some files bzipNormal could give you both better compression rate and higher speed than zlibMax.
So we strongly recommend you to test the above compression levels with your application data, to make an optimal choice.

The most advanced users of SFS editions with source code could also tune the parameters of compression algorithms to achieve the best result for their specific tasks.

Encryption algorithm
Password protection is provided by the Rijndael encryption algorithm (AES), 256 bit key.


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