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Change mbedtls_mpi_cmp_mpi_ct to check less than

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The signature of mbedtls_mpi_cmp_mpi_ct() meant to support using it in
place of mbedtls_mpi_cmp_mpi(). This meant full comparison functionality
and a signed result.

To make the function more universal and friendly to constant time
coding, we change the result type to unsigned. Theoretically, we could
encode the comparison result in an unsigned value, but it would be less
intuitive.

Therefore we won't be able to represent the result as unsigned anymore
and the functionality will be constrained to checking if the first
operand is less than the second. This is sufficient to support the
current use case and to check any relationship between MPIs.

The only drawback is that we need to call the function twice when
checking for equality, but this can be optimised later if an when it is
needed.
This commit is contained in:
Janos Follath 2019-10-11 14:21:53 +01:00
parent 4f6cf38016
commit 867a3abff5
5 changed files with 71 additions and 70 deletions
Download patch file Download diff file Expand all files Collapse all files

44
tests/suites/test_suite_mpi.data
View file

@ -163,38 +163,38 @@ mbedtls_mpi_cmp_mpi:10:"2":10:"-3":1
Base test mbedtls_mpi_cmp_mpi (Mixed values) #6
mbedtls_mpi_cmp_mpi:10:"-2":10:"31231231289798":-1
Base test mbedtls_mpi_cmp_mpi_ct #1
mbedtls_mpi_cmp_mpi_ct:1:10:"693":1:10:"693":0:0
Base test mbedtls_mpi_lt_mpi_ct #1
mbedtls_mpi_lt_mpi_ct:1:10:"693":1:10:"693":0:0
Base test mbedtls_mpi_cmp_mpi_ct #2
mbedtls_mpi_cmp_mpi_ct:1:10:"693":1:10:"692":1:0
Base test mbedtls_mpi_lt_mpi_ct #2
mbedtls_mpi_lt_mpi_ct:1:10:"693":1:10:"692":0:0
Base test mbedtls_mpi_cmp_mpi_ct #3
mbedtls_mpi_cmp_mpi_ct:1:10:"693":1:10:"694":-1:0
Base test mbedtls_mpi_lt_mpi_ct #3
mbedtls_mpi_lt_mpi_ct:1:10:"693":1:10:"694":1:0
Base test mbedtls_mpi_cmp_mpi_ct (Negative values) #1
mbedtls_mpi_cmp_mpi_ct:1:10:"-2":1:10:"-2":0:0
Base test mbedtls_mpi_lt_mpi_ct (Negative values) #1
mbedtls_mpi_lt_mpi_ct:1:10:"-2":1:10:"-2":0:0
Base test mbedtls_mpi_cmp_mpi_ct (Negative values) #2
mbedtls_mpi_cmp_mpi_ct:1:10:"-2":1:10:"-3":1:0
Base test mbedtls_mpi_lt_mpi_ct (Negative values) #2
mbedtls_mpi_lt_mpi_ct:1:10:"-2":1:10:"-3":0:0
Base test mbedtls_mpi_cmp_mpi_ct (Negative values) #3
mbedtls_mpi_cmp_mpi_ct:1:10:"-2":1:10:"-1":-1:0
Base test mbedtls_mpi_lt_mpi_ct (Negative values) #3
mbedtls_mpi_lt_mpi_ct:1:10:"-2":1:10:"-1":1:0
Base test mbedtls_mpi_cmp_mpi_ct (Mixed values) #4
mbedtls_mpi_cmp_mpi_ct:1:10:"-3":1:10:"2":-1:0
Base test mbedtls_mpi_lt_mpi_ct (Mixed values) #4
mbedtls_mpi_lt_mpi_ct:1:10:"-3":1:10:"2":1:0
Base test mbedtls_mpi_cmp_mpi_ct (Mixed values) #5
mbedtls_mpi_cmp_mpi_ct:1:10:"2":1:10:"-3":1:0
Base test mbedtls_mpi_lt_mpi_ct (Mixed values) #5
mbedtls_mpi_lt_mpi_ct:1:10:"2":1:10:"-3":0:0
Base test mbedtls_mpi_cmp_mpi_ct (Mixed values) #6
mbedtls_mpi_cmp_mpi_ct:2:10:"-2":2:10:"31231231289798":-1:0
Base test mbedtls_mpi_lt_mpi_ct (Mixed values) #6
mbedtls_mpi_lt_mpi_ct:2:10:"-2":2:10:"31231231289798":1:0
Base test mbedtls_mpi_cmp_mpi_ct (X is longer in storage) #7
mbedtls_mpi_cmp_mpi_ct:3:10:"693":2:10:"693":0:MBEDTLS_ERR_MPI_BAD_INPUT_DATA
Base test mbedtls_mpi_lt_mpi_ct (X is longer in storage) #7
mbedtls_mpi_lt_mpi_ct:3:10:"693":2:10:"693":0:MBEDTLS_ERR_MPI_BAD_INPUT_DATA
Base test mbedtls_mpi_cmp_mpi_ct (Y is longer in storage) #8
mbedtls_mpi_cmp_mpi_ct:3:10:"693":4:10:"693":0:MBEDTLS_ERR_MPI_BAD_INPUT_DATA
Base test mbedtls_mpi_lt_mpi_ct (Y is longer in storage) #8
mbedtls_mpi_lt_mpi_ct:3:10:"693":4:10:"693":0:MBEDTLS_ERR_MPI_BAD_INPUT_DATA
Base test mbedtls_mpi_cmp_abs #1
mbedtls_mpi_cmp_abs:10:"693":10:"693":0

12
tests/suites/test_suite_mpi.function
View file

@ -538,10 +538,12 @@ exit:
/* END_CASE */
/* BEGIN_CASE */
void mbedtls_mpi_cmp_mpi_ct( int size_X, int radix_X, char * input_X, int size_Y,
int radix_Y, char * input_Y, int input_ret, int input_err )
void mbedtls_mpi_lt_mpi_ct( int size_X, int radix_X, char * input_X,
int size_Y, int radix_Y, char * input_Y,
int input_ret, int input_err )
{
int ret;
unsigned ret;
unsigned input_uret = input_ret;
mbedtls_mpi X, Y;
mbedtls_mpi_init( &X ); mbedtls_mpi_init( &Y );
@ -551,9 +553,9 @@ void mbedtls_mpi_cmp_mpi_ct( int size_X, int radix_X, char * input_X, int size_Y
mbedtls_mpi_grow( &X, size_X );
mbedtls_mpi_grow( &Y, size_Y );
TEST_ASSERT( mbedtls_mpi_cmp_mpi_ct( &X, &Y, &ret ) == input_err );
TEST_ASSERT( mbedtls_mpi_lt_mpi_ct( &X, &Y, &ret ) == input_err );
if( input_err == 0 )
TEST_ASSERT( ret == input_ret );
TEST_ASSERT( ret == input_uret );
exit:
mbedtls_mpi_free( &X ); mbedtls_mpi_free( &Y );