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Make a public version of mpi_montg_init() in bignum_new.c and add unit tests

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The unit tests were created by capturing runs of the existing function during
execution of existing unit tests.

Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
This commit is contained in:
Tom Cosgrove
2022-08-17 06:17:00 +01:00
parent 659c84add9
commit 79b70f6394
5 changed files with 108 additions and 11 deletions
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11
library/bignum.c
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@ -1550,16 +1550,7 @@ int mbedtls_mpi_mod_int( mbedtls_mpi_uint *r, const mbedtls_mpi *A, mbedtls_mpi_
*/
static void mpi_montg_init( mbedtls_mpi_uint *mm, const mbedtls_mpi *N )
{
mbedtls_mpi_uint x, m0 = N->p[0];
unsigned int i;
x = m0;
x += ( ( m0 + 2 ) & 4 ) << 1;
for( i = biL; i >= 8; i /= 2 )
x *= ( 2 - ( m0 * x ) );
*mm = ~x + 1;
*mm = mbedtls_mpi_montg_init( N->p[0] );
}
/** Montgomery multiplication: A = A * B * R^-1 mod N (HAC 14.36)

13
library/bignum_core.h
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@ -171,7 +171,7 @@ int mbedtls_mpi_core_write_be( const mbedtls_mpi_uint *A,
* This must be odd and have exactly \p n limbs.
* \param[in] n The number of limbs in \p X, \p A, \p N.
* \param mm The Montgomery constant for \p N: -N^-1 mod 2^ciL.
* This can be calculated by `mpi_montg_init()`.
* This can be calculated by `mbedtls_mpi_montg_init()`.
* \param[in,out] T Temporary storage of size at least 2*n+1 limbs.
* Its initial content is unused and
* its final content is indeterminate.
@ -182,6 +182,17 @@ void mbedtls_mpi_core_montmul( mbedtls_mpi_uint *X,
const mbedtls_mpi_uint *N, size_t n,
mbedtls_mpi_uint mm, mbedtls_mpi_uint *T );
/**
* \brief Calculate initialisation value for fast Montgomery modular
* multiplication
*
* \param m0 The least-significant mbedtls_mpi_uint from the modulus, which
* must be odd
*
* \return The initialisation value for fast Montgomery modular multiplication
*/
mbedtls_mpi_uint mbedtls_mpi_montg_init( mbedtls_mpi_uint m0 );
/**
* \brief Perform a known-size multiply accumulate operation: d += b * s
*

15
library/bignum_new.c
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@ -56,6 +56,21 @@ void mbedtls_mpi_core_montmul( mbedtls_mpi_uint *X,
(void) mbedtls_mpi_core_add_if( X, N, n, ( carry < borrow ) );
}
/*
* Fast Montgomery initialization (thanks to Tom St Denis).
*/
mbedtls_mpi_uint mbedtls_mpi_montg_init( mbedtls_mpi_uint m0 )
{
mbedtls_mpi_uint x = m0;
x += ( ( m0 + 2 ) & 4 ) << 1;
for( unsigned int i = biL; i >= 8; i /= 2 )
x *= ( 2 - ( m0 * x ) );
return( ~x + 1 );
}
mbedtls_mpi_uint mbedtls_mpi_core_mla( mbedtls_mpi_uint *d, size_t d_len,
const mbedtls_mpi_uint *s, size_t s_len,
mbedtls_mpi_uint b )