Provided by: libgfshare1_1.0.2-0ubuntu3_i386 bug

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  recombined
       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 © 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
       distribution).  There is NO WARRANTY, to the extent permitted by law.

SEE ALSO

       gfsplit(1), gfcombine(1), gfshare(7)