Make mpn_cnd_add_n and mpn_cnd_sub_n public.

4 files changed, 27 insertions, 4 deletions

diff --git a/ChangeLog b/ChangeLog
index 717ee28c0..52484c087 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2013-03-26  Niels Möller  <nisse@lysator.liu.se>
+
+	Make mpn_cnd_add_n and mpn_cnd_sub_n public.
+	* doc/gmp.texi (Low-level Functions): Document mpn_cnd_add_n and
+	mpn_cnd_sub_n.
+	* gmp-h.in (mpn_cnd_add_n, mpn_cnd_sub_n): Moved prototypes
+	here...
+	* gmp-impl.h: ... from here.
+
 2013-03-26  Torbjorn Granlund  <tege@gmplib.org>
 
 	* mpn/x86/pentium4/sse2/cnd_add_n.asm: New file.
diff --git a/doc/gmp.texi b/doc/gmp.texi
index 6d49a2730..37e4bb772 100644
--- a/doc/gmp.texi
+++ b/doc/gmp.texi
@@ -5654,6 +5654,19 @@ Copy from @{@var{s1p}, @var{n}@} to @{@var{rp}, @var{n}@}, decreasingly.
 Zero @{@var{rp}, @var{n}@}.
 @end deftypefun
 
+@deftypefun void mpn_cnd_add_n (mp_limb_t @var{cnd}, mp_limb_t *@var{rp}, const mp_limb_t *@var{s1p}, const mp_limb_t *@var{s2p}, mp_size_t @var{n})
+@deftypefunx void mpn_cnd_sub_n (mp_limb_t @var{cnd}, mp_limb_t *@var{rp}, const mp_limb_t *@var{s1p}, const mp_limb_t *@var{s2p}, mp_size_t @var{n})
+These functions do conditional addition and subtraction, and are intended for
+cryptographic applications where resilience to side-channel attacks is
+desired. If @var{cnd} is non-zero, they produce the same result as a regular
+@code{mpn_add_n} or @code{mpn_sub_n}, and if @var{cnd} is zero, they copy
+@{@var{s1p},@var{n}@} to the result area and return zero. The functions are
+designed to have timing and memory access patterns depending only on size and
+location of the data areas, but independent of the condition @var{cnd}. Like
+for @code{mpn_add_n} and @code{mpn_sub_n}, on most machines, the timing will
+also be independent of the actual limb values.
+@end deftypefun
+
 @sp 1
 @section Nails
 @cindex Nails
diff --git a/gmp-h.in b/gmp-h.in
index 4e95480a0..c925350cf 100644
--- a/gmp-h.in
+++ b/gmp-h.in
@@ -1626,6 +1626,11 @@ __GMP_DECLSPEC void mpn_copyd (mp_ptr, mp_srcptr, mp_size_t);
 #define mpn_zero __MPN(zero)
 __GMP_DECLSPEC void mpn_zero (mp_ptr, mp_size_t);
 
+#define mpn_cnd_add_n __MPN(cnd_add_n)
+__GMP_DECLSPEC mp_limb_t mpn_cnd_add_n (mp_limb_t, mp_ptr, mp_srcptr, mp_srcptr, mp_size_t);
+#define mpn_cnd_sub_n __MPN(cnd_sub_n)
+__GMP_DECLSPEC mp_limb_t mpn_cnd_sub_n (mp_limb_t, mp_ptr, mp_srcptr, mp_srcptr, mp_size_t);
+
 /**************** mpz inlines ****************/
 
 /* The following are provided as inlines where possible, but always exist as
diff --git a/gmp-impl.h b/gmp-impl.h
index 0dd581296..43de7c8da 100644
--- a/gmp-impl.h
+++ b/gmp-impl.h
@@ -1555,10 +1555,6 @@ __GMP_DECLSPEC void      mpn_powm_sec (mp_ptr, mp_srcptr, mp_size_t, mp_srcptr,
 __GMP_DECLSPEC mp_size_t mpn_powm_sec_itch (mp_size_t, mp_size_t, mp_size_t);
 #define   mpn_tabselect __MPN(tabselect)
 __GMP_DECLSPEC void      mpn_tabselect (volatile mp_limb_t *, volatile mp_limb_t *, mp_size_t, mp_size_t, mp_size_t);
-#define   mpn_cnd_add_n __MPN(cnd_add_n)
-__GMP_DECLSPEC mp_limb_t mpn_cnd_add_n (mp_limb_t, mp_ptr, mp_srcptr, mp_srcptr, mp_size_t);
-#define   mpn_cnd_sub_n __MPN(cnd_sub_n)
-__GMP_DECLSPEC mp_limb_t mpn_cnd_sub_n (mp_limb_t, mp_ptr, mp_srcptr, mp_srcptr, mp_size_t);
 
 #define mpn_sb_div_qr_sec __MPN(sb_div_qr_sec)
 __GMP_DECLSPEC void mpn_sb_div_qr_sec (mp_ptr, mp_ptr, mp_size_t, mp_srcptr, mp_size_t, mp_ptr);