From f921f4d228e7176f7473cf8cb9c337d945ef1761 Mon Sep 17 00:00:00 2001 From: Gabor Mezei Date: Fri, 14 Apr 2023 15:11:14 +0200 Subject: [PATCH] Use loop for two passes in the reduction Signed-off-by: Gabor Mezei --- library/ecp_curves.c | 69 ++++++++++++++------------------------------ 1 file changed, 22 insertions(+), 47 deletions(-) diff --git a/library/ecp_curves.c b/library/ecp_curves.c index 1376f5d8f..36ee90094 100644 --- a/library/ecp_curves.c +++ b/library/ecp_curves.c @@ -5528,7 +5528,6 @@ static inline int ecp_mod_koblitz(mbedtls_mpi *N, mbedtls_mpi_uint *Rp, size_t p size_t adjust, size_t shift, mbedtls_mpi_uint mask) { int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; - size_t i; mbedtls_mpi M, R; mbedtls_mpi_uint Mp[P_KOBLITZ_MAX + P_KOBLITZ_R + 1]; @@ -5545,55 +5544,31 @@ static inline int ecp_mod_koblitz(mbedtls_mpi *N, mbedtls_mpi_uint *Rp, size_t p M.s = 1; M.p = Mp; - /* M = A1 */ - M.n = N->n - (p_limbs - adjust); - if (M.n > p_limbs + adjust) { - M.n = p_limbs + adjust; - } - memset(Mp, 0, sizeof(Mp)); - memcpy(Mp, N->p + p_limbs - adjust, M.n * sizeof(mbedtls_mpi_uint)); - if (shift != 0) { - MBEDTLS_MPI_CHK(mbedtls_mpi_shift_r(&M, shift)); - } - M.n += R.n; /* Make room for multiplication by R */ + for (size_t pass = 0; pass < 2; pass++) { + /* M = A1 */ + M.n = N->n - (p_limbs - adjust); + if (M.n > p_limbs + adjust) { + M.n = p_limbs + adjust; + } + memset(Mp, 0, sizeof(Mp)); + memcpy(Mp, N->p + p_limbs - adjust, M.n * sizeof(mbedtls_mpi_uint)); + if (shift != 0) { + MBEDTLS_MPI_CHK(mbedtls_mpi_shift_r(&M, shift)); + } + M.n += R.n; /* Make room for multiplication by R */ - /* N = A0 */ - if (mask != 0) { - N->p[p_limbs - 1] &= mask; - } - for (i = p_limbs; i < N->n; i++) { - N->p[i] = 0; - } + /* N = A0 */ + if (mask != 0) { + N->p[p_limbs - 1] &= mask; + } + for (size_t i = p_limbs; i < N->n; i++) { + N->p[i] = 0; + } - /* N = A0 + R * A1 */ - MBEDTLS_MPI_CHK(mbedtls_mpi_mul_mpi(&M, &M, &R)); - MBEDTLS_MPI_CHK(mbedtls_mpi_add_abs(N, N, &M)); - - /* Second pass */ - - /* M = A1 */ - M.n = N->n - (p_limbs - adjust); - if (M.n > p_limbs + adjust) { - M.n = p_limbs + adjust; + /* N = A0 + R * A1 */ + MBEDTLS_MPI_CHK(mbedtls_mpi_mul_mpi(&M, &M, &R)); + MBEDTLS_MPI_CHK(mbedtls_mpi_add_abs(N, N, &M)); } - memset(Mp, 0, sizeof(Mp)); - memcpy(Mp, N->p + p_limbs - adjust, M.n * sizeof(mbedtls_mpi_uint)); - if (shift != 0) { - MBEDTLS_MPI_CHK(mbedtls_mpi_shift_r(&M, shift)); - } - M.n += R.n; /* Make room for multiplication by R */ - - /* N = A0 */ - if (mask != 0) { - N->p[p_limbs - 1] &= mask; - } - for (i = p_limbs; i < N->n; i++) { - N->p[i] = 0; - } - - /* N = A0 + R * A1 */ - MBEDTLS_MPI_CHK(mbedtls_mpi_mul_mpi(&M, &M, &R)); - MBEDTLS_MPI_CHK(mbedtls_mpi_add_abs(N, N, &M)); cleanup: return ret;