Manpage of ppdecrypt
Section: User Commands (1)
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ppdecrypt - decrypt data for ppdd without kernel support
This program allows you to decrypt ppdd host files (or devices) without
Extra functionality (including an interface to pgp)
makes it useful also as a backup tool. As it is intended to be used only with
ppdd it makes use of the fact that the size of the data it is dealing with
is a multiple of 1024 bytes. It is not a general purpose decryption tool.
The program operates in two modes, ppdd and conventional.
In ppdd mode the program assumes that the first 1024 bytes of the input
file contain ppdd control information and that the rest corresponds one
to one with the decrypted data i.e. the second block of 1024 bytes will be
decrypted and form the second block of 1024 bytes in the output file.
In conventional mode the first 1024 bytes of the input file contain ppdd
information but the second block of 1024 bytes corresponds to the first
block of 1024 bytes in the output file.
If the input file was created by ppdncrypt in conventional mode then using
ppdecrypt in conventional mode will restore it exactly. If on the other hand
the file was encrypted by ppdncrypt in ppdd mode then using ppdecrypt in ppdd
mode will result in file identical to the original except that the first 1024
bytes will contain unspecified data. They must be restored some other way.
Why this is useful is explained in the documentation.
In ppdd mode the program can be run so as to overwrite the original file,
thus providing a decrypt in place facility. Unlike that offered by ppddpassw,
it does not require kernel support.
The program will ask for a pass phrase to use for decrypting the data.
Ppdncrypt provides an interface to pgp so as to enable backups to be made
using a public key.
The file produced in this way is suitable as input to ppdecrypt in pgp mode.
Note that pgp must have already been
installed correctly. A userid of "backup" must exist on the private keyring.
In pgp mode there is the choice of ppdd or conventional mode. This determines
whether the first 1024 bytes of the input file is included in the output file
or not. In ppdd mode the first 1024 bytes are excluded. The reasons why you
may want to exclude this block of data from the backup is explained in the
If any invalid combination of switches and arguments is used the program
displays a primitive help message. The number of arguments depends on the
In normal file copying mode the following are valid:
ppdecrypt input_file output_file
ppdecrypt -c input_file output_file
-c means preserve the first 1024 bytes
In all the above case a device (e.g. /dev/hda3) could substitute for a file,
either as input or output or both,
but the output device must be at least as large as the input.
In overwrite mode the following are valid:
ppdecrypt -o file_or_device
In pgp mode the following are valid:
ppdecrypt -p input_file output_file_or_device
ppdecrypt -pc input_file output_file_or_device
The program returns 0 if everything worked as expected.
The program returns 1 if anything has gone wrong.
All ppdd utilities display fairly meaningful errors (mostly on stderr).
In all cases the errors have a unique error number to help locate the
problem in the source code. If an error message is not clear then best
source of explanation at this stage is the source itself.
The program does not use any environment variables.
Files (and devices) are specified as arguments.
(c) 1999 Allan Latham - version 0.9
- RETURN VALUE
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This document was created by
using the manual pages.
Time: 16:39:01 GMT, September 14, 1999