X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/73fb671fe92c5de50a3cef58befe4b5294e73474..025c5f4aa5ffbf8948482a4233318db81c2df5d2:/gfshare.h

diff --git a/gfshare.h b/gfshare.h
index 29ecd14..a53d137 100644
--- a/gfshare.h
+++ b/gfshare.h
@@ -1,8 +1,8 @@
 /* -*-c-*-
  *
- * $Id: gfshare.h,v 1.2 2000/06/17 11:05:27 mdw Exp $
+ * $Id: gfshare.h,v 1.7 2004/04/08 01:36:15 mdw Exp $
  *
- * Secret sharing over %$\gf(2^8)$%
+ * Secret sharing over %$\gf{2^8}$%
  *
  * (c) 2000 Straylight/Edgeware
  */
@@ -27,24 +27,13 @@
  * MA 02111-1307, USA.
  */
 
-/*----- Revision history --------------------------------------------------* 
- *
- * $Log: gfshare.h,v $
- * Revision 1.2  2000/06/17 11:05:27  mdw
- * Add a commentary on the system.
- *
- * Revision 1.1  2000/06/17 10:56:30  mdw
- * Fast but nonstandard secret sharing system.
- *
- */
-
 /*----- Notes on the system -----------------------------------------------*
  *
  * This uses a variant of Shamir's secret sharing system.  Shamir's original
  * system used polynomials modulo a large prime.  This implementation instead
- * uses the field %$\gf(2^8)$%, represented by
+ * uses the field %$\gf{2^8}$%, represented by
  *
- *   %$\gf(2)[x]/(x^8 + x^4 + x^3 + x^2 + 1)$%
+ *   %$\gf{2}[x]/(x^8 + x^4 + x^3 + x^2 + 1)$%
  *
  * and shares each byte of the secret independently.  It is therefore limited
  * to 255 players, although this probably isn't a serious limitation in
@@ -74,28 +63,21 @@
 
 /* --- A secret sharing context --- */
 
-typedef struct gfshare_pt {
-  octet x;				/* %$x$%-coordinate of the share */
-  octet *y;				/* Pointer to share payload */
-} gfshare_pt;
-
 typedef struct gfshare {
   unsigned t;				/* Threshold */
-  unsigned n;				/* The number of shares to make */
   unsigned i;				/* Next free slot in vector */
   size_t sz;				/* Size of the secret and shares */
-  octet *s;				/* The secret */
-  gfshare_pt *v;			/* Vector of share information */
+  octet *v;				/* Vector of share information */
 } gfshare;
 
-#define GFSHARE_INIT(t, n, sz) { t, n, 0, sz, 0, 0 }
+#define GFSHARE_INIT(t, sz) { t, 0, sz, 0 }
 
 /*----- Functions provided ------------------------------------------------*/
 
 /* --- @gfshare_create@ --- *
  *
  * Arguments:	@gfshare *s@ = pointer to share context to initialize
- *		@unsigned t, n@ = threshold parameters for the system
+ *		@unsigned t@ = threshold for the system
  *		@size_t sz@ = size of the secret
  *
  * Returns:	---
@@ -103,8 +85,7 @@ typedef struct gfshare {
  * Use:		Initializes a sharing context.
  */
 
-extern void gfshare_create(gfshare */*s*/, unsigned /*t*/, unsigned /*n*/,
-			   size_t /*sz*/);
+extern void gfshare_create(gfshare */*s*/, unsigned /*t*/, size_t /*sz*/);
 
 /* --- @gfshare_destroy@ --- *
  *
@@ -123,26 +104,40 @@ extern void gfshare_destroy(gfshare */*s*/);
  *
  * Arguments:	@gfshare *s@ = pointer to share context to fill in
  *		@grand *r@ = pointer to random number source
+ *		@const void *buf@ = pointer to the secret to share
  *
  * Returns:	---
  *
- * Use:		Generates @c->n@ secret shares, such that any @c->t@ of them
- *		may be used to recover the secret.
- *
+ * Use:		Initializes a sharing context to be able to create shares.
  *		The context structure is expected to be mostly filled in.  In
- *		particular, @t@, @n@, @ssz@ and @s@ must be initialized.  If
- *		@v@ is zero, a vector of appropriate size is allocated.  You
- *		should use the macro @GFSHARE_INIT@ or @gfshare_create@ to
- *		construct sharing contexts.
+ *		particular, @t@ must be initialized.  If @v@ is zero, a
+ *		vector of appropriate size is allocated.  You should use the
+ *		macro @GFSHARE_INIT@ or @gfshare_create@ to construct sharing
+ *		contexts.
+ */
+
+extern void gfshare_mkshares(gfshare */*s*/, grand */*r*/,
+			     const void */*buf*/);
+
+/* --- @gfshare_get@ --- *
+ *
+ * Arguments:	@gfshare *s@ = pointer to share conext
+ *		@unsigned x@ = share index to fetch
+ *		@void *buf@ = pointer to output buffer
+ *
+ * Returns:	---
+ *
+ * Use:		Extracts a share from the system.  You may extract up to 255
+ *		shares from the system.  Shares are indexed from 0.
  */
 
-extern void gfshare_mkshares(gfshare */*s*/, grand */*r*/);
+extern void gfshare_get(gfshare */*s*/, unsigned /*x*/, void */*buf*/);
 
 /* --- @gfshare_add@ --- *
  *
  * Arguments:	@gfshare *s@ = pointer to sharing context
  *		@unsigned x@ = which share number this is
- *		@const octet *y@ = the share value
+ *		@const void *y@ = the share value
  *
  * Returns:	Number of shares required before recovery may be performed.
  *
@@ -151,19 +146,19 @@ extern void gfshare_mkshares(gfshare */*s*/, grand */*r*/);
  */
 
 extern unsigned gfshare_add(gfshare */*s*/,
-			    unsigned /*x*/, const octet */*y*/);
+			    unsigned /*x*/, const void */*y*/);
 
 /* --- @gfshare_combine@ --- *
  *
  * Arguments:	@gfshare *s@ = pointer to share context
- *		@octet *buf@ = pointer to output buffer for the secret
+ *		@void *buf@ = pointer to output buffer for the secret
  *
  * Returns:	---
  *
  * Use:		Reconstructs a secret, given enough shares.
  */
 
-extern void gfshare_combine(gfshare */*s*/, octet */*buf*/);
+extern void gfshare_combine(gfshare */*s*/, void */*buf*/);
 
 /*----- That's all, folks -------------------------------------------------*/