Dear
Mbed TLS contributors,
We
are using mbedtls v4 for X.509 certificate verification on a
32 bit microcontroller. The device has an RTC chip and we
use its time for mbedtls by defining
MBEDTLS_PLATFORM_TIME_ALT. This is working so far.
The
compiler provides <time.h>, with time_t being a signed
32 bit type. I would like to stop mbedtls from using the
date and time functions of <time.h> and change
mbedtls_time_t to unsigned 32 bit to avoid the year
2038 problem (when signed 32 bit time_t will overflow). To
do this, I defined
#define
MBEDTLS_PLATFORM_TIME_TYPE_MACRO unsigned long
I
also changed the custom time function
(MBEDTLS_PLATFORM_TIME_ALT) to return unsigned values and I
defined MBEDTLS_PLATFORM_GMTIME_R_ALT and provided a custom
mbedtls_platform_gmtime_r() that accepts unsigned values.
When
I build mbedtls with these settings, I get an error from
tf_psa_crypto_check_config.h:
#if
defined(MBEDTLS_PLATFORM_TIME_TYPE_MACRO) &&\
( defined(MBEDTLS_PLATFORM_STD_TIME) ||\
defined(MBEDTLS_PLATFORM_TIME_ALT) )
#error
"MBEDTLS_PLATFORM_TIME_TYPE_MACRO and
MBEDTLS_PLATFORM_STD_TIME/MBEDTLS_PLATFORM_TIME_ALT cannot
be defined simultaneously"
#endif
I
wonder if this check is actually necessary or maybe a
mistake? Actually, I expected the opposite, i.e.
#if
defined(MBEDTLS_PLATFORM_TIME_TYPE_MACRO) &&\
!( defined(MBEDTLS_PLATFORM_STD_TIME) ||\
defined(MBEDTLS_PLATFORM_TIME_ALT) )
#error
"Must provide alternate time() function compatible with type
defined by MBEDTLS_PLATFORM_TIME_TYPE_MACRO"
#endif
Could
somebody please explain why MBEDTLS_PLATFORM_TIME_TYPE_MACRO
can’t be used with MBEDTLS_PLATFORM_TIME_ALT? Can/Should I
comment out the #error? I tried that and the library
compiles without errors, and the software using the library
also compiles without errors, but I have not yet checked, if
it actually works.
Best
regards,
Ralf
Huber
KION
Supply Chain Solutions