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Fix ECDSA signature verification edge-case

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For R and S equal to 1, ensure the public key is checked
for validity.

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
This commit is contained in:
Dave Rodgman
2022-08-10 11:26:24 +01:00
parent 535dccebdc
commit 4268731b2f
1 changed files with 3 additions and 0 deletions
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3
library/ecp.c
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@@ -2797,14 +2797,17 @@ static int mbedtls_ecp_mul_shortcuts( mbedtls_ecp_group *grp,
if( mbedtls_mpi_cmp_int( m, 0 ) == 0 ) if( mbedtls_mpi_cmp_int( m, 0 ) == 0 )
{ {
MBEDTLS_MPI_CHK( mbedtls_ecp_check_pubkey( grp, P ) );
MBEDTLS_MPI_CHK( mbedtls_ecp_set_zero( R ) ); MBEDTLS_MPI_CHK( mbedtls_ecp_set_zero( R ) );
} }
else if( mbedtls_mpi_cmp_int( m, 1 ) == 0 ) else if( mbedtls_mpi_cmp_int( m, 1 ) == 0 )
{ {
MBEDTLS_MPI_CHK( mbedtls_ecp_check_pubkey( grp, P ) );
MBEDTLS_MPI_CHK( mbedtls_ecp_copy( R, P ) ); MBEDTLS_MPI_CHK( mbedtls_ecp_copy( R, P ) );
} }
else if( mbedtls_mpi_cmp_int( m, -1 ) == 0 ) else if( mbedtls_mpi_cmp_int( m, -1 ) == 0 )
{ {
MBEDTLS_MPI_CHK( mbedtls_ecp_check_pubkey( grp, P ) );
MBEDTLS_MPI_CHK( mbedtls_ecp_copy( R, P ) ); MBEDTLS_MPI_CHK( mbedtls_ecp_copy( R, P ) );
if( mbedtls_mpi_cmp_int( &R->Y, 0 ) != 0 ) if( mbedtls_mpi_cmp_int( &R->Y, 0 ) != 0 )
MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &R->Y, &grp->P, &R->Y ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &R->Y, &grp->P, &R->Y ) );