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Make some fields of mbedtls_ecp_group public

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The Mbed TLS code relies heavily on reading certain fields of
mbedtls_ecp_group directly. Make these fields public. Require
that MBEDTLS_ECP_ALT alternative implementations have them.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-05-27 23:53:07 +02:00
parent cd07e22048
commit bf69ea5b8f
3 changed files with 22 additions and 14 deletions
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32
include/mbedtls/ecp.h
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@ -206,25 +206,33 @@ mbedtls_ecp_point;
* additions or subtractions. Therefore, it is only an approximative modular
* reduction. It must return 0 on success and non-zero on failure.
*
* \note Alternative implementations must keep the group IDs distinct. If
* two group structures have the same ID, then they must be
* identical.
*
* \note Alternative implementations of the ECP module must obey the
* following constraints.
* * Group IDs must be distinct: if two group structures have
* the same ID, then they must be identical.
* * The fields \c id, \c P, \c A, \c B, \c G, \c N,
* \c pbits and \c nbits must have the same type and semantics
* as in the built-in implementation.
* They must be available for reading, but direct modification
* of these fields does not need to be supported.
* They do not need to be at the same offset in the structure.
*/
typedef struct mbedtls_ecp_group
{
mbedtls_ecp_group_id MBEDTLS_PRIVATE(id); /*!< An internal group identifier. */
mbedtls_mpi MBEDTLS_PRIVATE(P); /*!< The prime modulus of the base field. */
mbedtls_mpi MBEDTLS_PRIVATE(A); /*!< For Short Weierstrass: \p A in the equation. For
mbedtls_ecp_group_id id; /*!< An internal group identifier. */
mbedtls_mpi P; /*!< The prime modulus of the base field. */
mbedtls_mpi A; /*!< For Short Weierstrass: \p A in the equation. For
Montgomery curves: <code>(A + 2) / 4</code>. */
mbedtls_mpi MBEDTLS_PRIVATE(B); /*!< For Short Weierstrass: \p B in the equation.
mbedtls_mpi B; /*!< For Short Weierstrass: \p B in the equation.
For Montgomery curves: unused. */
mbedtls_ecp_point MBEDTLS_PRIVATE(G); /*!< The generator of the subgroup used. */
mbedtls_mpi MBEDTLS_PRIVATE(N); /*!< The order of \p G. */
size_t MBEDTLS_PRIVATE(pbits); /*!< The number of bits in \p P.*/
size_t MBEDTLS_PRIVATE(nbits); /*!< For Short Weierstrass: The number of bits in \p P.
mbedtls_ecp_point G; /*!< The generator of the subgroup used. */
mbedtls_mpi N; /*!< The order of \p G. */
size_t pbits; /*!< The number of bits in \p P.*/
size_t nbits; /*!< For Short Weierstrass: The number of bits in \p P.
For Montgomery curves: the number of bits in the
private keys. */
/* End of public fields */
unsigned int MBEDTLS_PRIVATE(h); /*!< \internal 1 if the constants are static. */
int (*MBEDTLS_PRIVATE(modp))(mbedtls_mpi *); /*!< The function for fast pseudo-reduction
mod \p P (see above).*/

2
programs/pkey/ecdsa.c
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@ -156,7 +156,7 @@ int main( int argc, char *argv[] )
goto exit;
}
mbedtls_printf( " ok (key size: %d bits)\n", (int) ctx_sign.MBEDTLS_PRIVATE(grp).MBEDTLS_PRIVATE(pbits) );
mbedtls_printf( " ok (key size: %d bits)\n", (int) ctx_sign.MBEDTLS_PRIVATE(grp).pbits );
dump_pubkey( " + Public key: ", &ctx_sign );

2
programs/pkey/gen_key.c
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@ -395,7 +395,7 @@ int main( int argc, char *argv[] )
{
mbedtls_ecp_keypair *ecp = mbedtls_pk_ec( key );
mbedtls_printf( "curve: %s\n",
mbedtls_ecp_curve_info_from_grp_id( ecp->MBEDTLS_PRIVATE(grp).MBEDTLS_PRIVATE(id) )->MBEDTLS_PRIVATE(name) );
mbedtls_ecp_curve_info_from_grp_id( ecp->MBEDTLS_PRIVATE(grp).id )->MBEDTLS_PRIVATE(name) );
mbedtls_mpi_write_file( "X_Q: ", &ecp->MBEDTLS_PRIVATE(Q).MBEDTLS_PRIVATE(X), 16, NULL );
mbedtls_mpi_write_file( "Y_Q: ", &ecp->MBEDTLS_PRIVATE(Q).MBEDTLS_PRIVATE(Y), 16, NULL );
mbedtls_mpi_write_file( "D: ", &ecp->MBEDTLS_PRIVATE(d) , 16, NULL );