Re: [PATCH] MPI helper of comparison, Least Leak Intended (was: [PATCH] MPI helper of multiplication, Least Leak Intended)
NIIBE Yutaka via Gcrypt-devel <[email protected]>
| Newsgroups | gmane.comp.encryption.gpg.libgcrypt.devel |
|---|---|
| Message-ID | <[email protected]> |
NIIBE Yutaka <[email protected]> wrote: > I think that this implementation could be improved. I should use ct_limb_gen_inv_mask function instead of directly use unary minus operator. -- _______________________________________________ Gcrypt-devel mailing list [email protected] https://lists.gnupg.org/mailman/listinfo/gcrypt-devel
0001-mpi-Add-_gcry_mpih_cmp_lli-for-Least-Leak-Intended-c.patch
(text/x-diff, 1.9 KB)
>From 6edebbb2573e1a0e1bc66b6c5162826e579795c1 Mon Sep 17 00:00:00 2001 From: NIIBE Yutaka <[email protected]> Date: Sat, 8 Feb 2025 11:00:18 +0900 Subject: [PATCH] mpi: Add _gcry_mpih_cmp_lli for Least Leak Intended comparison. * mpi/mpi-internal.h (_gcry_mpih_cmp_lli): New. * mpi/mpih-const-time.c (_gcry_mpih_cmp_lli): New. -- Signed-off-by: NIIBE Yutaka <[email protected]> --- mpi/mpi-internal.h | 1 + mpi/mpih-const-time.c | 22 ++++++++++++++++++++++ 2 files changed, 23 insertions(+) diff --git a/mpi/mpi-internal.h b/mpi/mpi-internal.h index ffe8140a..0840d1fd 100644 --- a/mpi/mpi-internal.h +++ b/mpi/mpi-internal.h @@ -304,6 +304,7 @@ void _gcry_mpih_abs_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_ptr_t _gcry_mpih_mod_lli (mpi_ptr_t vp, mpi_size_t vsize, mpi_ptr_t up, mpi_size_t usize); int _gcry_mpih_cmp_ui (mpi_ptr_t up, mpi_size_t usize, unsigned long v); +int _gcry_mpih_cmp_lli (mpi_ptr_t up, mpi_ptr_t vp, mpi_size_t size); /* Define stuff for longlong.h. */ diff --git a/mpi/mpih-const-time.c b/mpi/mpih-const-time.c index e684b956..7c783492 100644 --- a/mpi/mpih-const-time.c +++ b/mpi/mpih-const-time.c @@ -239,3 +239,25 @@ _gcry_mpih_cmp_ui (mpi_ptr_t up, mpi_size_t usize, unsigned long v) } return 1; } + +/* Do same calculation as _gcry_mpih_cmp does, but Least Leak Intended. + * Return 1 if U > V, 0 if they are equal, and -1 if U < V. */ +int +_gcry_mpih_cmp_lli (mpi_ptr_t up, mpi_ptr_t vp, mpi_size_t size) +{ + mpi_size_t i; + mpi_limb_t gt, lt; + mpi_limb_t result = 0; + + for (i = 0; i < size ; i++) + { + gt = mpih_ct_limb_greater_than (up[i], vp[i]); + lt = mpih_ct_limb_less_than (up[i], vp[i]); + /* result = gt ? 1 : result; */ + result = (result & ct_limb_gen_inv_mask (gt)) | gt; + /* result = lt ? -1 : result; */ + result = (result & ct_limb_gen_inv_mask (lt)) | -lt; + } + + return (int)result; +} -- 2.39.5