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mbedtls_ecp_gen_privkey: create subfunctions for each curve type

Browse source 
Put the Montgomery and short Weierstrass implementations of
mbedtls_ecp_gen_privkey into their own function which can be tested
independently, but will not be part of the public ABI/API.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-03-23 22:31:31 +01:00
parent 48f052fb35
commit de33213f23
2 changed files with 147 additions and 76 deletions
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59
library/ecp.c
View file

@ -3040,28 +3040,14 @@ int mbedtls_ecp_check_privkey( const mbedtls_ecp_group *grp,
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
}
/*
* Generate a private key
*/
int mbedtls_ecp_gen_privkey( const mbedtls_ecp_group *grp,
#if defined(MBEDTLS_ECP_MONTGOMERY_ENABLED)
MBEDTLS_STATIC_TESTABLE
int mbedtls_ecp_gen_privkey_mx( size_t n_bits,
mbedtls_mpi *d,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
size_t n_bits;
const mbedtls_mpi *N = NULL;
ECP_VALIDATE_RET( grp != NULL );
ECP_VALIDATE_RET( d != NULL );
ECP_VALIDATE_RET( f_rng != NULL );
N = &grp->N;
n_bits = grp->nbits;
#if defined(MBEDTLS_ECP_MONTGOMERY_ENABLED)
if( mbedtls_ecp_get_type( grp ) == MBEDTLS_ECP_TYPE_MONTGOMERY )
{
size_t b;
size_t n_bytes = ( n_bits + 7 ) / 8;
@ -3085,13 +3071,21 @@ int mbedtls_ecp_gen_privkey( const mbedtls_ecp_group *grp,
{
MBEDTLS_MPI_CHK( mbedtls_mpi_set_bit( d, 2, 0 ) );
}
cleanup:
return( ret );
}
#endif /* MBEDTLS_ECP_MONTGOMERY_ENABLED */
#if defined(MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED)
if( mbedtls_ecp_get_type( grp ) == MBEDTLS_ECP_TYPE_SHORT_WEIERSTRASS )
MBEDTLS_STATIC_TESTABLE
int mbedtls_ecp_gen_privkey_sw( const mbedtls_mpi *N, size_t n_bits,
mbedtls_mpi *d,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
/* SEC1 3.2.1: Generate d such that 1 <= n < N */
int ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
int count = 0;
unsigned cmp = 0;
size_t n_bytes = ( n_bits + 7 ) / 8;
@ -3131,12 +3125,37 @@ int mbedtls_ecp_gen_privkey( const mbedtls_ecp_group *grp,
}
}
while( mbedtls_mpi_cmp_int( d, 1 ) < 0 || cmp != 1 );
}
#endif /* MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED */
cleanup:
return( ret );
}
#endif /* MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED */
/*
* Generate a private key
*/
int mbedtls_ecp_gen_privkey( const mbedtls_ecp_group *grp,
mbedtls_mpi *d,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
ECP_VALIDATE_RET( grp != NULL );
ECP_VALIDATE_RET( d != NULL );
ECP_VALIDATE_RET( f_rng != NULL );
#if defined(MBEDTLS_ECP_MONTGOMERY_ENABLED)
if( mbedtls_ecp_get_type( grp ) == MBEDTLS_ECP_TYPE_MONTGOMERY )
return( mbedtls_ecp_gen_privkey_mx( grp->nbits, d, f_rng, p_rng ) );
#endif /* MBEDTLS_ECP_MONTGOMERY_ENABLED */
#if defined(MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED)
if( mbedtls_ecp_get_type( grp ) == MBEDTLS_ECP_TYPE_SHORT_WEIERSTRASS )
return( mbedtls_ecp_gen_privkey_sw( &grp->N, grp->nbits, d,
f_rng, p_rng ) );
#endif /* MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED */
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
}
/*
* Generate a keypair with configurable base point

52
library/ecp_invasive.h
View file

@ -27,6 +27,7 @@
#define MBEDTLS_ECP_INVASIVE_H
#include "common.h"
#include "mbedtls/bignum.h"
#include "mbedtls/ecp.h"
#if defined(MBEDTLS_TEST_HOOKS) && defined(MBEDTLS_ECP_C)
@ -46,6 +47,57 @@
void mbedtls_ecp_fix_negative( mbedtls_mpi *N, signed char c, size_t bits );
#endif
#if defined(MBEDTLS_ECP_MONTGOMERY_ENABLED)
/** Generate a private key on a Montgomery curve (Curve25519 or Curve448).
*
* This function implements key generation for the set of secret keys
* specified in [Curve25519] p. 5 and in [Curve448]. The resulting value
* has the lower bits masked but is not necessarily canonical.
*
* \note - [Curve25519] http://cr.yp.to/ecdh/curve25519-20060209.pdf
* - [RFC7748] https://tools.ietf.org/html/rfc7748
*
* \p n_bits The position of the high-order bit of the key to generate.
* This is the bit-size of the key minus 1:
* 254 for Curve25519 or 447 for Curve448.
* \param d The randomly generated key. This is a number of size
* exactly \p n_bits + 1 bits, with the least significant bits
* masked as specified in [Curve25519] and in [RFC7748] §5.
* \param f_rng The RNG function.
* \param p_rng The RNG context to be passed to \p f_rng.
*
* \return \c 0 on success.
* \return \c MBEDTLS_ERR_ECP_xxx or MBEDTLS_ERR_MPI_xxx on failure.
*/
int mbedtls_ecp_gen_privkey_mx( size_t n_bits,
mbedtls_mpi *d,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng );
#endif /* MBEDTLS_ECP_MONTGOMERY_ENABLED */
#if defined(MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED)
/** Generate a private key on a short Weierstrass curve.
*
* The procedure complies with RFC 6979 §3.3 (deterministic ECDSA)
* when the RNG is a suitably parametrized instance of HMAC_DRBG.
*
* \p N The upper bound of the range.
* \p n_bits The size of \p N in bits. This value must be correct,
* otherwise the result is unpredictable.
* \param d A random number, uniformly generated in the range [1, N-1].
* \param f_rng The RNG function.
* \param p_rng The RNG context to be passed to \p f_rng.
*
* \return \c 0 on success.
* \return \c MBEDTLS_ERR_ECP_xxx or MBEDTLS_ERR_MPI_xxx on failure.
*/
int mbedtls_ecp_gen_privkey_sw( const mbedtls_mpi *N, size_t n_bits,
mbedtls_mpi *d,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng );
#endif /* MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED */
#endif /* MBEDTLS_TEST_HOOKS && MBEDTLS_ECP_C */
#endif /* MBEDTLS_ECP_INVASIVE_H */