From ae48111294929d5416574c4d0de3c916494639d1 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Manuel=20P=C3=A9gouri=C3=A9-Gonnard?= Date: Wed, 23 Jun 2021 12:43:34 +0200 Subject: [PATCH] Use more compact encoding of Montgomery curve constants MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Base 256 beats base 16. Signed-off-by: Manuel Pégourié-Gonnard --- library/ecp_curves.c | 30 ++++++++++++++++++++++++------ 1 file changed, 24 insertions(+), 6 deletions(-) diff --git a/library/ecp_curves.c b/library/ecp_curves.c index 4797cf4bd..3acc5a496 100644 --- a/library/ecp_curves.c +++ b/library/ecp_curves.c @@ -685,6 +685,13 @@ static int ecp_mod_p256k1( mbedtls_mpi * ); #endif /* ECP_LOAD_GROUP */ #if defined(MBEDTLS_ECP_DP_CURVE25519_ENABLED) +/* Constants used by ecp_use_curve25519() */ +static const unsigned char curve25519_a24[] = { 0x01, 0xDB, 0x42 }; +static const unsigned char curve25519_part_of_n[] = { + 0x14, 0xDE, 0xF9, 0xDE, 0xA2, 0xF7, 0x9C, 0xD6, + 0x58, 0x12, 0x63, 0x1A, 0x5C, 0xF5, 0xD3, 0xED, +}; + /* * Specialized function for creating the Curve25519 group */ @@ -693,7 +700,8 @@ static int ecp_use_curve25519( mbedtls_ecp_group *grp ) int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; /* Actually ( A + 2 ) / 4 */ - MBEDTLS_MPI_CHK( mbedtls_mpi_read_string( &grp->A, 16, "01DB42" ) ); + MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( &grp->A, + curve25519_a24, sizeof( curve25519_a24 ) ) ); /* P = 2^255 - 19 */ MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &grp->P, 1 ) ); @@ -702,8 +710,8 @@ static int ecp_use_curve25519( mbedtls_ecp_group *grp ) grp->pbits = mbedtls_mpi_bitlen( &grp->P ); /* N = 2^252 + 27742317777372353535851937790883648493 */ - MBEDTLS_MPI_CHK( mbedtls_mpi_read_string( &grp->N, 16, - "14DEF9DEA2F79CD65812631A5CF5D3ED" ) ); + MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( &grp->N, + curve25519_part_of_n, sizeof( curve25519_part_of_n ) ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_set_bit( &grp->N, 252, 1 ) ); /* Y intentionally not set, since we use x/z coordinates. @@ -746,6 +754,15 @@ const mbedtls_mpi mbedtls_ecp_x25519_bad_point_2 = ECP_MPI_INIT_ARRAY( #endif /* MBEDTLS_ECP_DP_CURVE25519_ENABLED */ #if defined(MBEDTLS_ECP_DP_CURVE448_ENABLED) +/* Constants used by ecp_use_curve448() */ +static const unsigned char curve448_a24[] = { 0x98, 0xAA }; +static const unsigned char curve448_part_of_n[] = { + 0x83, 0x35, 0xDC, 0x16, 0x3B, 0xB1, 0x24, + 0xB6, 0x51, 0x29, 0xC9, 0x6F, 0xDE, 0x93, + 0x3D, 0x8D, 0x72, 0x3A, 0x70, 0xAA, 0xDC, + 0x87, 0x3D, 0x6D, 0x54, 0xA7, 0xBB, 0x0D, +}; + /* * Specialized function for creating the Curve448 group */ @@ -757,7 +774,8 @@ static int ecp_use_curve448( mbedtls_ecp_group *grp ) mbedtls_mpi_init( &Ns ); /* Actually ( A + 2 ) / 4 */ - MBEDTLS_MPI_CHK( mbedtls_mpi_read_string( &grp->A, 16, "98AA" ) ); + MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( &grp->A, + curve448_a24, sizeof( curve448_a24 ) ) ); /* P = 2^448 - 2^224 - 1 */ MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &grp->P, 1 ) ); @@ -775,8 +793,8 @@ static int ecp_use_curve448( mbedtls_ecp_group *grp ) /* N = 2^446 - 13818066809895115352007386748515426880336692474882178609894547503885 */ MBEDTLS_MPI_CHK( mbedtls_mpi_set_bit( &grp->N, 446, 1 ) ); - MBEDTLS_MPI_CHK( mbedtls_mpi_read_string( &Ns, 16, - "8335DC163BB124B65129C96FDE933D8D723A70AADC873D6D54A7BB0D" ) ); + MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( &Ns, + curve448_part_of_n, sizeof( curve448_part_of_n ) ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &grp->N, &grp->N, &Ns ) ); /* Actually, the required msb for private keys */