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Add Montgomery points to ecp_point_write_binary

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The library is able to perform computations and cryptographic schemes on
curves with x coordinate ladder representation. Here we add the
capability to export such points.
This commit is contained in:
Janos Follath
2019-02-20 12:00:22 +00:00
parent ab0f71a22a
commit 7caf8e452f
2 changed files with 51 additions and 28 deletions
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71
library/ecp.c
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@ -729,7 +729,7 @@ cleanup:
}
/*
* Export a point into unsigned binary data (SEC1 2.3.3)
* Export a point into unsigned binary data (SEC1 2.3.3 and RFC7748)
*/
int mbedtls_ecp_point_write_binary( const mbedtls_ecp_group *grp,
const mbedtls_ecp_point *P,
@ -745,43 +745,58 @@ int mbedtls_ecp_point_write_binary( const mbedtls_ecp_group *grp,
ECP_VALIDATE_RET( format == MBEDTLS_ECP_PF_UNCOMPRESSED ||
format == MBEDTLS_ECP_PF_COMPRESSED );
/*
* Common case: P == 0
*/
if( mbedtls_mpi_cmp_int( &P->Z, 0 ) == 0 )
{
if( buflen < 1 )
return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );
buf[0] = 0x00;
*olen = 1;
return( 0 );
}
plen = mbedtls_mpi_size( &grp->P );
if( format == MBEDTLS_ECP_PF_UNCOMPRESSED )
#if defined(ECP_MONTGOMERY)
if( ecp_get_type( grp ) == ECP_TYPE_MONTGOMERY )
{
*olen = 2 * plen + 1;
*olen = plen;
if( buflen < *olen )
return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );
return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );
buf[0] = 0x04;
MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &P->X, buf + 1, plen ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &P->Y, buf + 1 + plen, plen ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary_le( &P->X, buf, plen ) );
}
else if( format == MBEDTLS_ECP_PF_COMPRESSED )
#endif
#if defined(ECP_SHORTWEIERSTRASS)
if( ecp_get_type( grp ) != ECP_TYPE_MONTGOMERY )
{
*olen = plen + 1;
/*
* Common case: P == 0
*/
if( mbedtls_mpi_cmp_int( &P->Z, 0 ) == 0 )
{
if( buflen < 1 )
return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );
if( buflen < *olen )
return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );
buf[0] = 0x00;
*olen = 1;
buf[0] = 0x02 + mbedtls_mpi_get_bit( &P->Y, 0 );
MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &P->X, buf + 1, plen ) );
return( 0 );
}
if( format == MBEDTLS_ECP_PF_UNCOMPRESSED )
{
*olen = 2 * plen + 1;
if( buflen < *olen )
return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );
buf[0] = 0x04;
MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &P->X, buf + 1, plen ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &P->Y, buf + 1 + plen, plen ) );
}
else if( format == MBEDTLS_ECP_PF_COMPRESSED )
{
*olen = plen + 1;
if( buflen < *olen )
return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );
buf[0] = 0x02 + mbedtls_mpi_get_bit( &P->Y, 0 );
MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &P->X, buf + 1, plen ) );
}
}
#endif
cleanup:
return( ret );