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Fix Failure in Cryptocell tests on Montgomrery curve #11512

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merged 1 commit into from
Oct 15, 2019
Merged

Fix Failure in Cryptocell tests on Montgomrery curve #11512

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55 changes: 52 additions & 3 deletions features/cryptocell/FEATURE_CRYPTOCELL310/ecdh_alt.c
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Original file line number Diff line number Diff line change
Expand Up @@ -201,6 +201,7 @@ int mbedtls_ecdh_compute_shared( mbedtls_ecp_group *grp, mbedtls_mpi *z,
}
else if ( grp->id == MBEDTLS_ECP_DP_CURVE25519 )
{
uint8_t temp_buf[CURVE_25519_KEY_SIZE] = {0};
cc_ecc_25519_comp_shared_params_t* ecdhParams = mbedtls_calloc( 1, sizeof(cc_ecc_25519_comp_shared_params_t) );
if ( ecdhParams == NULL )
{
Expand All @@ -211,18 +212,66 @@ int mbedtls_ecdh_compute_shared( mbedtls_ecp_group *grp, mbedtls_mpi *z,
pHeap = ecdhParams;
heapSize = sizeof(cc_ecc_25519_comp_shared_params_t);

if( mbedtls_mpi_size( d ) != CURVE_25519_KEY_SIZE )
{
ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
goto cleanup;
}
MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( d, temp_buf,
mbedtls_mpi_size( d ) ) ) ;
ret = convert_CrysError_to_mbedtls_err(
CRYS_COMMON_ConvertLswMswWordsToMsbLsbBytes( ecdhParams->privKey,
CURVE_25519_KEY_SIZE,
(uint32_t*)temp_buf,
sizeof( temp_buf) ) );
if ( ret != 0 )
{
mbedtls_platform_zeroize( temp_buf, sizeof(temp_buf) );
goto cleanup;
}

MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( d, ecdhParams->privKey, mbedtls_mpi_size( d ) ) ) ;
MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &Q->X, ecdhParams->pubKey, public_key_size ) );
if( public_key_size != CURVE_25519_KEY_SIZE )
{
ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
goto cleanup;
}

ret = convert_CrysError_to_mbedtls_err( CRYS_ECMONT_Scalarmult( secret, ( size_t* )&secret_size,
MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &Q->X, temp_buf, public_key_size ) );
ret = convert_CrysError_to_mbedtls_err(
CRYS_COMMON_ConvertLswMswWordsToMsbLsbBytes( ecdhParams->pubKey,
CURVE_25519_KEY_SIZE,
(uint32_t*)temp_buf,
sizeof( temp_buf) ) );
if ( ret != 0 )
{
mbedtls_platform_zeroize( temp_buf, sizeof(temp_buf) );
goto cleanup;
}

if( secret_size != CURVE_25519_KEY_SIZE )
{
ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
goto cleanup;
}

ret = convert_CrysError_to_mbedtls_err( CRYS_ECMONT_Scalarmult( temp_buf, ( size_t* )&secret_size,
ecdhParams->privKey, CURVE_25519_KEY_SIZE ,
ecdhParams->pubKey, CURVE_25519_KEY_SIZE ,
&ecdhParams->kgTempData ) );
if ( ret != 0 )
{
goto cleanup;
}
ret = convert_CrysError_to_mbedtls_err(
CRYS_COMMON_ConvertLswMswWordsToMsbLsbBytes( secret,
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Shouldn't this conversion go the other way? We have converted the private and public key to the MsbLsbBytes so that CRYS_ECMONT_Scalarmult() can operate on them, but I would expect the output temp_buf to still be in that encoding. If we now want to operate on it further, outside the Cryptocell world, I'd expect the temp_buf to be converted to the LswMswWords again here.

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But this is what mbedtls_mpi_read_binary() does in line 282.
Note that this operation was added after the test vector in our tests failed, so the output of this function is now as expected outside the Cryptocell world

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Thanks for the clarification 👍

secret_size,
(uint32_t*)temp_buf,
CURVE_25519_KEY_SIZE ) );
if ( ret != 0 )
{
mbedtls_platform_zeroize( temp_buf, sizeof(temp_buf) );
goto cleanup;
}
}
else
{
Expand Down