GFCOMBINE(1) UserCommands GFCOMBINE(1)NAME
gfcombine - combine a number of shares to form the original file
SYNOPSIS
gfcombine [-o OUTPUTFILE] INPUTFILE...
DESCRIPTION
Combine a set of files (as produced by gfsplit) to produce the original file by interpolating the shares on the commandline.
-o OUTPUTFILE
The name of the file to write out.
All INPUTFILEs should be called something.NNN where the .NNN is the share number. (The gfsplit tool will output files named appropriately).
The OUTPUTFILE if omitted will default to the name of the first INPUTFILE with the .NNN removed.
AUTHOR
Written by Daniel Silverstone.
REPORTING BUGS
Report bugs against the libgfshare product on www.launchpad.net.
COPYRIGHT
Copyright (C) 2006 Daniel Silverstone.
This is free software. You may redistribute copies of it under the terms of the MIT licence (the COPYRIGHT file in the source distribu-
tion). There is NO WARRANTY, to the extent permitted by law.
SEE ALSO gfsplit(1), libgfshare(3), gfshare(7)1.0.5 February 2006 GFCOMBINE(1)
Check Out this Related Man Page
LIBGFSHARE(5) Shamir Secret Sharing in gf(2**8) LIBGFSHARE(5)NAME
gfshare_ctx_init_enc, etc. - Shamir Secret Sharing
SYNOPSIS
#include <libgfshare.h>
gfshare_ctx *gfshare_ctx_init_enc( unsigned char *sharenrs,
unsigned int sharecount,
unsigned char threshold,
unsigned int size );
gfshare_ctx *gfshare_ctx_init_dec( unsigned char *sharenrs,
unsigned int sharecount,
unsigned int size );
void gfshare_ctx_free( gfshare_ctx *ctx );
void gfshare_ctx_enc_setsecret( gfshare_ctx *ctx,
unsigned char *secret );
void gfshare_ctx_enc_getshare( gfshare_ctx *ctx,
unsigned char sharenr,
unsigned char *share );
void gfshare_ctx_dec_newshares( gfshare_ctx *ctx,
unsigned char *sharenrs );
void gfshare_ctx_dec_giveshare( gfshare_ctx *ctx,
unsigned char sharenr,
unsigned char *share );
void gfshare_ctx_dec_extract( gfshare_ctx *ctx,
unsigned char *secretbuf );
DESCRIPTION
The gfshare_ctx_init_enc() function returns a context object which can be used for encoding shares of a secret. The context encodes against
sharecount shares which are numbered in the array sharenrs. The secret is always size bytes long and the resultant shares will need at
least threshold of the shares present for recombination. It is critical that threshold be at least one lower than sharecount.
The gfshare_ctx_init_dec() function returns a context object which can be used to recombine shares to recover a secret. Each share and the
resulting secret will be size bytes long. The context can be used to recombine sharecount shares which are numbered in the sharenrs array.
The gfshare_ctx_free() function frees all the memory associated with a gfshare context including the memory belonging to the context
itself.
The gfshare_ctx_enc_setsecret() function provides the secret you wish to encode to the context. The secret will be copied into the internal
buffer of the library.
The gfshare_ctx_enc_getshare() function extracts a particular share from the context. The share buffer must be preallocated to the size of
the shares and the sharenr parameter is an index into the sharenrs array used to initialise the context
The gfshare_ctx_dec_newshares() function informs the decode context of a change in the share numbers available to the context. The number
of shares cannot be changed but the sharenrs can be zero to indicate that a particular share is missing currently.
The gfshare_ctx_dec_giveshare() function provides the decode context with a given share. The share number itself was previously provided in
a sharenrs array and the sharenr parameter is the index into that array of the number of the share being provided in the share memory
block.
The gfshare_ctx_dec_extract() function combines the provided shares to recalculate the secret. It is recommended that you mlock() the
secretbuf before calling this function, so that the recombined secret will never be written to swap. This may help to prevent a malicious
party discovering the content of your secret. You should also randomise the content of the buffer once you are finished using the recom-
bined secret.
ERRORS
Any function which can fail for any reason will return NULL on error.
AUTHOR
Written by Daniel Silverstone.
REPORTING BUGS
Report bugs against the libgfshare product on www.launchpad.net.
COPYRIGHT
Copyright (C) 2006 Daniel Silverstone.
This is free software. You may redistribute copies of it under the terms of the MIT licence (the COPYRIGHT file in the source distribu-
tion). There is NO WARRANTY, to the extent permitted by law.
SEE ALSO gfsplit(1), gfcombine(1), gfshare(7)1.0.5 February 2006 LIBGFSHARE(5)