X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/a5b0f8ff5c3b7150e853db4744791dbc4daf2d33..d4bb7fded5f9a4b0db99f82e88f22effe94f2ff7:/ct.h

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+/* -*-c-*-
+ *
+ * Constant-time operations
+ *
+ * (c) 2013 Straylight/Edgeware
+ */
+
+/*----- Licensing notice --------------------------------------------------*
+ *
+ * This file is part of Catacomb.
+ *
+ * Catacomb is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Library General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * Catacomb is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with Catacomb; if not, write to the Free
+ * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+ * MA 02111-1307, USA.
+ */
+
+#ifndef CATACOMB_CT_H
+#define CATACOMB_CT_H
+
+#ifdef __cplusplus
+  extern "C" {
+#endif
+
+/*----- Header files ------------------------------------------------------*/
+
+#include <mLib/bits.h>
+
+/*----- Functions provided ------------------------------------------------*/
+
+/* --- @ct_inteq@ --- *
+ *
+ * Arguments:	@uint32 x, y@ = two 32-bit unsigned integers
+ *
+ * Returns:	One if @x@ and @y@ are equal, zero if they differ.
+ *
+ * Use:		Answers whether two integers are equal, in constant time.
+ */
+
+extern int ct_inteq(uint32 /*x*/, uint32 /*y*/);
+
+/* --- @ct_intle@ --- *
+ *
+ * Arguments:	@uint32 x, y@ = two 32-bit unsigned integers
+ *
+ * Returns:	One if %$x \le y$% are equal, zero if @x@ is greater.
+ *
+ * Use:		Answers whether two integers are ordered, in constant time.
+ */
+
+extern int ct_intle(uint32 /*x*/, uint32 /*y*/);
+
+/* --- @ct_pick@ --- *
+ *
+ * Arguments:	@uint32 a@ = a switch, either zero or one
+ *		@uint32 x0, x1@ = two 32-bit unsigned integers
+ *
+ * Returns:	@x0@ if @a@ is zero; @x1@ if @a@ is one.  Other values of @a@
+ *		will give you unhelpful results.
+ *
+ * Use:		Picks one of two results according to a switch variable, in
+ *		constant time.
+ */
+
+extern int ct_pick(uint32 /*a*/, uint32 /*x0*/, uint32 /*x1*/);
+
+/* --- @ct_condcopy@ --- *
+ *
+ * Arguments:	@uint32 a@ = a switch, either zero or one
+ *		@void *d@ = destination pointer
+ *		@const void *s@ = source pointer
+ *		@size_t n@ amount to copy
+ *
+ * Returns:	---
+ *
+ * Use:		If @a@ is one then copy the @n@ bytes starting at @s@ to
+ *		@d@; if @a@ is zero then leave @d@ unchanged (but it will
+ *		still be written).  All of this is done in constant time.
+ */
+
+extern void ct_condcopy(uint32 /*a*/,
+			void */*d*/, const void */*s*/, size_t /*n*/);
+
+/* --- @ct_memeq@ ---
+ *
+ * Arguments:	@const void *p, *q@ = two pointers to buffers
+ *		@size_t n@ = the (common) size of the buffers
+ *
+ * Returns:	One if the two buffers are equal, zero if they aren't.
+ *
+ * Use:		Compares two chunks of memory, in constant time.
+ */
+
+extern int ct_memeq(const void */*p*/, const void */*q*/, size_t /*n*/);
+
+/*----- That's all, folks -------------------------------------------------*/
+
+#ifdef __cplusplus
+  }
+#endif
+
+#endif