The library style is to start with the includes corresponding to the
current module and then the rest in alphabetical order. Some modules
have several header files (eg. ssl_internal.h).
The recently added error.h includes did not respect this convention and
this commit restores it. In some cases this is not possible just by
moving the error.h declarations. This commit fixes the pre-existing
order in these instances too.
Using 4096 bytes of stack for the temporary buffer used for holding a
throw-away DER-formatted CSR limits the portability of generating
certificate signing requests to only devices with lots of stack space.
To increase portability, use the mbedtls_pem_write_buffer() in-place
capability instead, using the same buffer for input and output. This
works since the DER encoding for some given data is always smaller than
that same data PEM-encoded.
PEM format is desirable to use even on stack-constrained devices as the
format is easy to work with (for example, copy-pasting from a tiny
device's serial console output, for CSRs generated on tiny devices
without the private key leaving said tiny device).
Add a new function mbedtls_asn1_write_named_bitstring() that removes
trailing 0s at the end of DER encoded bitstrings. The function is
implemented according to Hanno Becker's suggestions.
This commit also changes the functions x509write_crt_set_ns_cert_type
and crt_set_key_usage to call the new function as the use named
bitstrings instead of the regular bitstrings.
This commit removes all the static occurrencies of the function
mbedtls_zeroize() in each of the individual .c modules. Instead the
function has been moved to utils.h that is included in each of the
modules.
