SDN (SDN Project)

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File Format
Name SDN (SDN Project)
Extension(s) .sdn, .sda
Released 1989

An .SDN file is a compressed archive file associated with the SDN Project organization, and the SDNet/Works! software distribution network. SDN stands for Shareware Distribution Network. SDN files are cryptographically authenticated.

An SDN file might be accompanied by, or might contain, an .SDA "abstract" file. This is apparently just a text file describing the software in the SDN file.



There are at least two or three different SDN formats.

PAK-based format

The original format is a PAK file with a special extended record. PAK itself is a variant of ARC.

SDNV format

The documentation for the SDNV utility says:

SDN FILES BEFORE JUNE 15TH 1990.........................................
Files with  a .SDN extension  that were  packaged before June  15th 1990
were compressed using NoGate Consulting's PAK v2.10 utility. [...]

SDN FILES AFTER JUNE 15TH 1990..........................................
All files and programs, released  for distribution on SDNet/Works! after
June 15th  1990 will be  secured and  compressed in SDNV  format.  Other
archivers will not be able to read  or uncompress these .SDN files.  You
must use a the  SDNV utility SDNV.EXE. [...]

More research is needed, but it seems possible that the plan to switch to SDNV format was abandoned.

ARJ-based format

In 1993, it was announced[1] that SDN files would switch to a format based on ARJ, and FSecure by PaceSoft.

ARJ v2.39c (early 1993) simultaneously changed ARJ's native "security envelope" format, and claimed to introduce "SDN support". This is confusing, because these two similar features are not really related (though SDN files might well use both).

And ARJ doesn't actually fully validate SDN-secured files. The claimed "SDN support" appears to be referring to some convenience features related to identifying SDN files as such, and telling the user what to do.


PAK format:

SDNV format:

ARJ format:

Sample files

PAK format:

(Wanted: ARJ-SDN samples.)


  1. fido1004.txt → "SDN Changing Compression and Security"
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