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mpi_core_mod_exp: improve style and documentation

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No intended change in behaviour.

Signed-off-by: Janos Follath <janos.follath@arm.com>
This commit is contained in:
Janos Follath 2022-11-14 12:52:08 +00:00
parent a77911e5c1
commit 0ec6e3f394
2 changed files with 31 additions and 30 deletions
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49
library/bignum_core.c
View File

@ -597,11 +597,11 @@ static size_t exp_mod_get_window_size( size_t Ebits )
}
int mbedtls_mpi_core_exp_mod( mbedtls_mpi_uint *X,
mbedtls_mpi_uint const *A,
const mbedtls_mpi_uint *A,
const mbedtls_mpi_uint *N,
size_t n,
size_t AN_limbs,
const mbedtls_mpi_uint *E,
size_t E_len,
size_t E_limbs,
const mbedtls_mpi_uint *RR )
{
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@ -616,15 +616,15 @@ int mbedtls_mpi_core_exp_mod( mbedtls_mpi_uint *X,
mbedtls_mpi_uint one = 1, mm;
mm = mbedtls_mpi_core_montmul_init( N ); /* Compute Montgomery constant */
E += E_len; /* Skip to end of exponent buffer */
E += E_limbs; /* Skip to end of exponent buffer */
wsize = exp_mod_get_window_size( E_len * biL );
wsize = exp_mod_get_window_size( E_limbs * biL );
welem = ( (size_t) 1 ) << wsize;
/* Allocate memory pool and set pointers to parts of it */
const size_t table_limbs = welem * n;
const size_t temp_limbs = 2 * n + 1;
const size_t wselect_limbs = n;
const size_t table_limbs = welem * AN_limbs;
const size_t temp_limbs = 2 * AN_limbs + 1;
const size_t wselect_limbs = AN_limbs;
const size_t total_limbs = table_limbs + temp_limbs + wselect_limbs;
mempool = mbedtls_calloc( total_limbs, sizeof(mbedtls_mpi_uint) );
@ -643,25 +643,26 @@ int mbedtls_mpi_core_exp_mod( mbedtls_mpi_uint *X,
*/
/* W[0] = 1 (in Montgomery presentation) */
memset( Wtbl, 0, n * ciL ); Wtbl[0] = 1;
mbedtls_mpi_core_montmul( Wtbl, Wtbl, RR, n, N, n, mm, temp );
Wcur = Wtbl + n;
memset( Wtbl, 0, AN_limbs * ciL );
Wtbl[0] = 1;
mbedtls_mpi_core_montmul( Wtbl, Wtbl, RR, AN_limbs, N, AN_limbs, mm, temp );
Wcur = Wtbl + AN_limbs;
/* W[1] = A * R^2 * R^-1 mod N = A * R mod N */
memcpy( Wcur, A, n * ciL );
mbedtls_mpi_core_montmul( Wcur, Wcur, RR, n, N, n, mm, temp );
memcpy( Wcur, A, AN_limbs * ciL );
mbedtls_mpi_core_montmul( Wcur, Wcur, RR, AN_limbs, N, AN_limbs, mm, temp );
W1 = Wcur;
Wcur += n;
Wcur += AN_limbs;
/* W[i+1] = W[i] * W[1], i >= 2 */
Wlast = W1;
for( size_t i=2; i < welem; i++, Wlast += n, Wcur += n )
mbedtls_mpi_core_montmul( Wcur, Wlast, W1, n, N, n, mm, temp );
for( size_t i = 2; i < welem; i++, Wlast += AN_limbs, Wcur += AN_limbs )
mbedtls_mpi_core_montmul( Wcur, Wlast, W1, AN_limbs, N, AN_limbs, mm, temp );
/*
* Sliding window exponentiation
* Fixed window exponentiation
*/
/* X = 1 (in Montgomery presentation) initially */
memcpy( X, Wtbl, n * ciL );
memcpy( X, Wtbl, AN_limbs * ciL );
size_t limb_bits_remaining = 0;
mbedtls_mpi_uint cur_limb, window = 0;
@ -671,7 +672,7 @@ int mbedtls_mpi_core_exp_mod( mbedtls_mpi_uint *X,
size_t window_bits_missing = wsize - window_bits;
const int no_more_bits =
( limb_bits_remaining == 0 ) && ( E_len == 0 );
( limb_bits_remaining == 0 ) && ( E_limbs == 0 );
const int window_full =
( window_bits_missing == 0 );
@ -682,8 +683,8 @@ int mbedtls_mpi_core_exp_mod( mbedtls_mpi_uint *X,
break;
/* Select table entry, square and multiply */
mbedtls_mpi_core_ct_uint_table_lookup( Wselect, Wtbl,
n, welem, window );
mbedtls_mpi_core_montmul( X, X, Wselect, n, N, n, mm, temp );
AN_limbs, welem, window );
mbedtls_mpi_core_montmul( X, X, Wselect, AN_limbs, N, AN_limbs, mm, temp );
window = window_bits = 0;
continue;
}
@ -692,12 +693,12 @@ int mbedtls_mpi_core_exp_mod( mbedtls_mpi_uint *X,
if( limb_bits_remaining == 0 )
{
cur_limb = *--E;
E_len--;
E_limbs--;
limb_bits_remaining = biL;
}
/* Square */
mbedtls_mpi_core_montmul( X, X, X, n, N, n, mm, temp );
mbedtls_mpi_core_montmul( X, X, X, AN_limbs, N, AN_limbs, mm, temp );
/* Insert next exponent bit into window */
window <<= 1;
@ -708,7 +709,7 @@ int mbedtls_mpi_core_exp_mod( mbedtls_mpi_uint *X,
}
/* Convert X back to normal presentation */
mbedtls_mpi_core_montmul( X, X, &one, 1, N, n, mm, temp );
mbedtls_mpi_core_montmul( X, X, &one, 1, N, AN_limbs, mm, temp );
ret = 0;

12
library/bignum_core.h
View File

@ -503,21 +503,21 @@ int mbedtls_mpi_core_fill_random( mbedtls_mpi_uint *X, size_t X_limbs,
* X = A^E mod N
*
* \param[out] X The destination MPI, as a little endian array of length
* \p limbs.
* \param[in] A The base MPI, as a little endian array of length \p limbs.
* \param[in] N The modulus, as a little endian array of length \p limbs.
* \param limbs The number of limbs in \p X, \p A, \p N, \p RR.
* \p AN_limbs.
* \param[in] A The base MPI, as a little endian array of length \p AN_limbs.
* \param[in] N The modulus, as a little endian array of length \p AN_limbs.
* \param AN_limbs The number of limbs in \p X, \p A, \p N, \p RR.
* \param[in] E The exponent, as a little endian array of length \p E_limbs.
* \param E_limbs The number of limbs in \p E.
* \param[in] RR The precomputed residue of 2^{2*biL} modulo N, as a little
* endian array of length \p limbs.
* endian array of length \p AN_limbs.
*
* \return \c 0 if successful.
* \return #MBEDTLS_ERR_MPI_ALLOC_FAILED if a memory allocation failed.
*/
int mbedtls_mpi_core_exp_mod( mbedtls_mpi_uint *X,
const mbedtls_mpi_uint *A,
const mbedtls_mpi_uint *N, size_t limbs,
const mbedtls_mpi_uint *N, size_t AN_limbs,
const mbedtls_mpi_uint *E, size_t E_limbs,
const mbedtls_mpi_uint *RR );