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mbedtls_ecp_gen_privkey_sw: generalize to mbedtls_mpi_random

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Rename mbedtls_ecp_gen_privkey_sw to mbedtls_mpi_random since it has
no particular connection to elliptic curves beyond the fact that its
operation is defined by the deterministic ECDSA specification. This is
a generic function that generates a random MPI between 1 inclusive and
N exclusive.

Slightly generalize the function to accept a different lower bound,
which adds a negligible amount of complexity.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-03-29 21:53:58 +02:00
parent 7888073147
commit 8cfffb30b3
4 changed files with 119 additions and 99 deletions
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39
library/ecp_invasive.h
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@ -77,25 +77,36 @@ int mbedtls_ecp_gen_privkey_mx( size_t n_bits,
#endif /* MBEDTLS_ECP_MONTGOMERY_ENABLED */
#if defined(MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED)
/** Generate a private key on a short Weierstrass curve.
/** Generate a random number uniformly in a range.
*
* This function generates a random number between \p min inclusive and
* \p N exclusive.
*
* The procedure complies with RFC 6979 §3.3 (deterministic ECDSA)
* when the RNG is a suitably parametrized instance of HMAC_DRBG.
* when the RNG is a suitably parametrized instance of HMAC_DRBG
* and \p min is \c 1.
*
* \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.
* \note There are `N - min` possible outputs. The lower bound
* \p min can be reached, but the upper bound \p N cannot.
*
* \return \c 0 on success.
* \return \c MBEDTLS_ERR_ECP_xxx or MBEDTLS_ERR_MPI_xxx on failure.
* \param X The destination MPI. This must point to an initialized MPI.
* \param min The minimum value to return.
* It must be nonnegative.
* \param N The upper bound of the range, exclusive.
* In other words, this is one plus the maximum value to return.
* \p N must be strictly larger than \p min.
* \param f_rng The RNG function to use. This must not be \c NULL.
* \param p_rng The RNG parameter to be passed to \p f_rng.
*
* \return \c 0 if successful.
* \return #MBEDTLS_ERR_MPI_ALLOC_FAILED if a memory allocation failed.
* \return Another negative error code 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 );
int mbedtls_mpi_random( mbedtls_mpi *X,
mbedtls_mpi_sint min,
const mbedtls_mpi *N,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng );
#endif /* MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED */
#endif /* MBEDTLS_TEST_HOOKS && MBEDTLS_ECP_C */