This is a workaround for an issue with mkstemp() in older MinGW releases that
causes simultaneous creation of .a files in the same directory to fail.
Fixes#5146
Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
The makefile build specifies -L. -lmbedx509 -lmbedcrypto flags first,
and only then object files referencing symbols from those libraries.
In this order the linker will not add the linked libraries to the
DT_NEEDED section because they are not referenced yet (at least that
happens for me on ubuntu 20.04 with the default gnu compiler tools).
By first specifying the object files and then the linked libraries, we
do end up with libmbedx509 and libmbedcrypto in the DT_NEEDED sections.
This way running dlopen(...) on libmedtls.so just works.
Note that the CMake build does this by default.
Signed-off-by: Harmen Stoppels <harmenstoppels@gmail.com>
Don't regenerate configuration-independent files when config.h or
crypto_config.h changes. These files only depend on the set of symbols
present in the headers and not on which symbols are enabled. To avoid
rebuilding the generated files whenever the configuration changes,
don't declare the configuration as a dependency.
In the rare event that a maintainer makes an edit to *config.h that
affects the generated files, they'll have to remove the generated files.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Run `make generated_files` to generate the automatically generated
C source files and build scripts.
Run `make neat` to remove all automatically generated files, even C
source files and build scripts.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit adds an implementation of the MPS trace module
based on `printf()`.
The enabling macro MBEDTLS_MPS_TRACE remains unset by default
because MPS tracing is very verbose and consumes unnecessary
space in the CI.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
Add psa_crypto_cipher.[ch] files to contain the
Mbed TLS implementation of PSA driver cipher driver
entry points.
Signed-off-by: Ronald Cron <ronald.cron@arm.com>
Rename both `rsa_internal.h` and `rsa_internal.c` to more descriptive
names: `rsa_alt_helpers.h` and `rsa_alt_helpers.c`.
Also re-orders `rsa_internal.c` to match the order in `rsa_internal.h`
Signed-off-by: Chris Jones <christopher.jones@arm.com>
Executed ./scripts/bump_version.sh --version 2.25.0 --so-crypto 6
Increasing the SO version of the crypto library, because the openless
API improvement came with API/ABI incompatibilities. For example
- the size of psa_key_handle_t changed
- the type of a parameter in 18 public functions has changed from
psa_key_handle_t to mbedtls_svc_key_id_t
Signed-off-by: Janos Follath <janos.follath@arm.com>
This commit introduces a new file library/ssl_tls13_key.c
which will subsequently be populated with functionality relating
to the TLS 1.3 key schedule.
Those functions are expected to be internal and are documented
in the internal header library/ssl_tls13_keys.h.
The first function to be implemented is the key expansion
function `HKDF-Expand-Label`. See the documentation in
library/ssl_tls13_keys.h for more information.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
When compiling library files under `3rdparty/`, the directory containing
the `.c` file that is being compiled is not the current directory, so
headers from the `library/` directory are not found. Fix this by
adding `.` to the include path.
This was not detected until now because as of this commit, no 3rdparty
source file requires a header under `library/`.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Executed "./scripts/bump_version.sh --version 2.23.0 --so-crypto 5"
A symbol has been removed from the mbedcrypto library since the last
release:
mbedtls_ecc_group_to_psa ( enum mbedtls_ecp_group_id grpid,
size_t* bits )
This is an ABI break and we need to increase the SO version.
Signed-off-by: Janos Follath <janos.follath@arm.com>
A file generated based on the output of `make list` from programs has been
re-generated.
Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
This change was first introduced in 8af3923 - see this commit for more background.
After the removal of crypto directory, there are no targets that require a
crypto library with the directory prefix, so there's also no need for the priority
dependency to be declared. This commit removes it.
Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>
Remove code guarded by `USE_CRYPTO_SUBMODULE`. It's dead now that
crypto can no longer be a submodule.
In `library/Makefile`:
* Replace `$(CRYPTO_INCLUDE)` with the single include directory
`-I../include`.
* Remove references to `$(OBJS_CRYPTO)` when it's in addition to the
local objects (`*.o`) since `$(OBJS_CRYPTO)` is now a subset of the
local objects.
* Merge modules that were duplicated between the mbedtls and the
mbed-crypto repositories back into the single list for `OBJS_CRYPTO`.
Merge `unremove-non-crypto` into `mbedtls/development`. The branch
`unremove-non-crypto` was obtained by starting from `mbed-crypto/development`,
then reverting many commits that removed X.509 and TLS functionality when Mbed
Crypto forked from Mbed TLS (the “unremoval”), then make a few tweaks to
facilitate the merge.
The unremoval step restored old versions of some tls files. If a file doesn't
exist in mbed-crypto, check out the mbedtls version, regardless of what
happened during the unremoval of tls files in the crypto tree. Also
unconditionally take the mbedtls version of a few files where the
modifications are completely project-specific and are not relevant in
mbed-crypto:
* `.github/issue_template.md`: completely different. We may want to reconcile
them independently as a follow-up.
* `.travis.yml`: would only be reverted to an earlier tls version.
* `README.md`: completely different. We may want to reconcile them
independently as a follow-up.
* `doxygen/input/doc_mainpage.h`: the changes in crypto were minimal and not
relevant except as a stopgap as mbed-crypto did not have its own product
versioning in the Doxygen documentation.
* `tests/.jenkins/Jenkinsfile`: completely different.
* `tests/data_files/Makefile`: there were no changes in mbed-crypto,
but the unremoval step restored an old version.
Shell script for everything to do after the merge apart from the conflict
resolution:
```
tls_files=($(comm -23 <(git ls-tree -r --name-only HEAD) <(git ls-tree -r --name-only $(git merge-base upstream-crypto/development MERGE_HEAD))))
tls_files+=($tls_files .github/issue_template.md .travis.yml README.md doxygen/input/doc_mainpage.h tests/.jenkins/Jenkinsfile tests/data_files/Makefile)
git checkout --theirs HEAD -- $tls_files
git add -- $tls_files
```
Resolve the remaining conflicts:
* `library/CMakeLists.txt`:
* Keep the TLS definition of `src_crypto`
* `USE_SHARED_MBEDTLS_LIBRARY`: keep all three libraries, with both
`include` and `crypto/include` in `target_include_directories`, all with
version `2.21.0`.
* `programs/Makefile`:
* Reconcile the APPS lists (add/add from a differently-formatted common
ancestor): insert the `psa/*` from crypto into the tls list.
* Keep the `fuzz` target defined only in tls version.
* Keep the recipe (only in tls version) cleaning `ssl_pthread_server`
stuff for the `clean` target.
* `scripts/config.py`:
* `include_in_full`: add/add conflict. Keep both.
* `tests/scripts/all.sh`:
* `component_test_no_use_psa_crypto_full_cmake_asan`: partially old
version in crypto. Take the tls version.
* `component_test_malloc_0_null` and more: take
`component_test_malloc_0_null` from crypto (with `config.py` rather than
`config.pl`, and with `$ASAN_FLAGS` rather than an explicit list), but
add the call to `ssl-opt.sh` from tls. Take the other components from
crypto.
With this commit, building and running the unit tests with both `make ` and
`cmake` work in the default configuration on Linux. Other platforms, build
systems and configurations are likely not to work, and there is some
regression in test coverage.
There is some loss of functionality because the unremoval step restored older
versions of tls content. This commit contains the latest tls version of
tls-only files, but some changes from the tls side in files that existed on
both sides have regressed. Most problematic changes are hunks that remove some
tls-specific feature and contain either a C preprocessor symbol identifying a
tls-specific module or option, or the name of a tls-specific file. Hunks
that remove a tls-specific preprocessor symbol can be identified with the
regular expression `^-.*MBEDTLS_(ERR_)?(PKCS11|X509|NET|SSL)_`.
Subsequent commits will revert a few parts of the patch from this merge commit
in order to restore the tls functionality that it removes, ensure that the
test coverage includes what was covered in either branch, and fix test
failures.
This reverts commit 8298d70bee.
Conflicts:
* library/Makefile: removal of SOEXT_X509 and SOEXT_TLS vs change of
value of SOEXT_CRYPTO. Keep all, with the new value of SOEXT_CRYPTO.
This commit adds the newly created copy ssl_msg.c of ssl_tls.c
to the build system but guards its content by an `#if 0 ... #endif`
preprocessor guard in order to avoid compilation failures resulting
from code duplication. This guard will be removed once the contents
of ssl_tls.c and ssl_msg.c have been made disjoint.
This commit is the first in a series of commits aiming to split
the content of ssl_tls.c in two files ssl_tls.c and ssl_msg.c.
As a first step, this commit replaces ssl_tls.c by two identical
copies ssl_tls_old.c and ssl_msg.c. Even though the file
ssl_tls_old.c will subsequently be renamed back into ssl_tls.c,
this approach retains the git history in both files.
First deal with deleted files.
* Files deleted by us: keep them deleted.
* Files deleted by them, whether modified by us or not: keep our version.
```
git rm $(git status -s | sed -n 's/^DU //p')
git reset -- $(git status -s | sed -n 's/^D //p')
git checkout -- $(git status -s | sed -n 's/^ D //p')
git add -- $(git status -s | sed -n 's/^UD //p')
```
Individual files with conflicts:
* `3rdparty/everest/library/Hacl_Curve25519_joined.c`: spurious conflict because git mistakenly identified this file as a rename. Keep our version.
* `README.md`: conflict due to their change in a paragraph that doesn't exist in our version. Keep our version of this paragraph.
* `docs/architecture/Makefile`: near-identical additions. Adapt the definition of `all_markdown` and include the clean target.
* `doxygen/input/docs_mainpage.h`: conflict in the version number. Keep our version number.
* `include/mbedtls/config.h`: two delete/modify conflicts. Keep the removed chunks out.
* `library/CMakeLists.txt`: discard all their changes as they are not relevant.
* `library/Makefile`:
* Discard the added chunk about the crypto submodule starting with `INCLUDING_FROM_MBEDTLS:=1`.
* delete/modify: keep the removed chunk out.
* library build: This is almost delete/modify. Their changes are mostly not applicable. Do keep the `libmbedcrypto.$(DLEXT): | libmbedcrypto.a` order dependency.
* `.c.o`: `-o` was added on both sides but in a different place. Change to their place.
* `library/error.c`: to be regenerated.
* `library/version_features.c`: to be regenerated.
* `programs/Makefile`: Most of the changes are not relevant. The one relevant change is in the `clean` target for Windows; adapt it by removing `/S` from our version.
* `programs/test/query_config.c`: to be regenerated.
* `scripts/config.py`: added in parallel on both sides. Keep our version.
* `scripts/footprint.sh`: parallel changes. Keep our version.
* `scripts/generate_visualc_files.pl`: one delete/modify conflict. Keep the removed chunks out.
* `tests/Makefile`: discard all of their changes.
* `tests/scripts/all.sh`:
* `pre_initialize_variables` add `append_outcome`: add it.
* `pre_initialize_variables` add `ASAN_CFLAGS`: already there, keep our version.
* `pre_parse_command_line` add `--no-append-outcome`: add it.
* `pre_parse_command_line` add `--outcome-file`: add it.
* `pre_print_configuration`: add `MBEDTLS_TEST_OUTCOME_FILE`.
* Several changes in SSL-specific components: keep our version without them.
* Several changes where `config.pl` was changed to `config.py` and there was an adjacent difference: keep our version.
* Changes regarding the inclusion of `MBEDTLS_MEMORY_xxx`: ignore them here, they will be normalized in a subsequent commit.
* `component_test_full_cmake_gcc_asan`: add it without the TLS tests.
* `component_test_no_use_psa_crypto_full_cmake_asan`: keep the fixed `msg`, discard other changes.
* `component_test_memory_buffer_allocator_backtrace`, `component_test_memory_buffer_allocator`: add them without the TLS tests.
* `component_test_m32_everest`: added in parallel on both sides. Keep our version.
* `tests/scripts/check-names.sh`, `tests/scripts/list-enum-consts.pl`, `tests/scripts/list-identifiers.sh`, ``tests/scripts/list-macros.sh`: discard all of their changes.
* `tests/scripts/test-ref-configs.pl`: the change in the conflict is not relevant, so keep our version there.
* `visualc/VS2010/*.vcxproj`: to be regenerated.
Regenerate files:
```
scripts/generate_visualc_files.pl
git add visualc/VS2010/*.vcxproj
scripts/generate_errors.pl
git add library/error.c
scripts/generate_features.pl
git add library/version_features.c
scripts/generate_query_config.pl
git add programs/test/query_config.c
```
Rejected changes in non-conflicting files:
* `CMakeLists.txt`: discard their addition which has already been side-ported.
* `doxygen/mbedtls.doxyfile`: keep the version number change. Discard the changes related to `../crypto` paths.
Keep the following changes after examination:
* `.travis.yml`: all of their changes are relevant.
* `include/mbedtls/error.h`: do keep their changes. Even though Crypto doesn't use TLS errors, it must not encroach on TLS's allocated numbers.
* `tests/scripts/check-test-cases.py`: keep the code dealing with `ssl-opt.sh`. It works correctly when the file is not present.
This caused problems when running multiple jobs at once, since
there was no target matching libmbedcrypto.so with the path
prefix. It only worked if it was built first, since such file was found.
Additionally, building of libmbedcrypto.so now waits for the static .a version.
Previously, recipes for both libmbedcrypto.a and libmbedcrypto.so could run
independently when running parallel jobs, which resulted in the .o files
being built twice. It could sometimes be a problem, since linking would start
when building one of the object files was still in progress (the previous one
existed). This in turn resulted in reading (and trying to link) a malformed file.
The "|" character is followed by "order-only-prerequisites", and in this case,
makes linking of the shared version of the library wait for the .a file.
Since it's guaranteed to be always built in the "all" target, it's fine to do that.
All of the .o files are only built once thanks to this change.
If we try to delete a non-existant file using del on Windows, as
can happen when running make clean, del will throw an error. Make
the Makefiles more robust by only deleting files if they exist.
Bring Mbed TLS 2.18.0 and 2.18.1 release changes back into the
development branch. We had branched to release 2.18.0 and 2.18.1 in
order to allow those releases to go out without having to block work on
the `development` branch.
Manually resolve conflicts in the Changelog by moving all freshly addded
changes to a new, unreleased version entry.
Reject changes to include/mbedtls/platform.h made in the mbedtls-2.18
branch, as that file is now sourced from Mbed Crypto.
* mbedtls-2.18:
platform: Include stdarg.h where needed
Update Mbed Crypto to contain mbed-crypto#152
CMake: Add a subdirectory build regression test
README: Enable builds as a CMake subproject
ChangeLog: Enable builds as a CMake subproject
Remove use of CMAKE_SOURCE_DIR
Update library version to 2.18.0
Conflict resolution:
* `scripts/config.pl`:
Take the exclusion of `MBEDTLS_PSA_CRYPTO_SE_C` from the API branch.
Take the removal of `MBEDTLS_PSA_CRYPTO_STORAGE_ITS_C` (obsolete) from
the development branch.
* `tests/scripts/all.sh`:
Multiple instances of factoring a sequence of `config.pl` calls into
a mere `config.pl baremetal` in the development branch, and a change in
the composition of `baremetal` in the API branch. In each case, take the
version from development.
* `tests/suites/test_suite_psa_crypto_slot_management.function`:
A function became non-static in development and disappeared in the API
branch. Keep the version from the API branch. Functions need to be
non-static if they're defined but unused in some configurations,
which is not the case for any function in this file at the moment.
* `tests/suites/test_suite_psa_crypto.function`:
Consecutive changes in the two branches, reconciled.
Resolve conflicts by performing the following operations:
- Reject changes related to building a crypto submodule, since Mbed
Crypto is the crypto submodule.
- Reject X.509, NET, and SSL changes.
- Reject changes to README, as Mbed Crypto is a different project from
Mbed TLS, with a different README.
- Avoid adding mention of ssl-opt.sh in a comment near some modified
code in include/CMakeLists.txt (around where ENABLE_TESTING as added).
- Align config.pl in Mbed TLS with config.pl in Mbed Crypto where PSA
options are concerned, to make future merging easier. There is no
reason for the two to be different in this regard, now that Mbed TLS
always depends on Mbed Crypto. Remaining differences are only the
PSA_CRYPTO_KEY_FILE_ID_ENCODES_OWNER option and the absence of X.509,
NET, and SSL related options in Mbed Crypto's config.pl.
- Align config.h in Mbed Crypto with Mbed TLS's copy, with a few notable
exceptions:
- Leave CMAC on by default.
- Leave storage on by default (including ITS emulation).
- Avoid documenting the PSA Crypto API as is in beta stage in
documentation for MBEDTLS_PSA_CRYPTO_C.
The only remaining differences are a lack of X.509, NET, and SSL
options in Mbed Crypto's config.h, as well as an additional
Mbed-Crypto-specific PSA_CRYPTO_KEY_FILE_ID_ENCODES_OWNER option.
Documentation for the check params feature and related macros is also
updated to match Mbed TLS's description.
- Reject tests/data_files/Makefile changes to generate DER versions of
CRTs and keys, as none of those are used by Mbed Crypto tests.
- Add the "no PEM and no filesystem" test to all.sh, without ssl-opt.sh
run, as Mbed Crypto doesn't have ssl-opt.sh. Also remove use of PSA
Crypto storage and ITS emulation, since those depend on filesystem
support.
- Reject addition of test when no ciphersuites have MAC to all.sh, as
the option being tested, MBEDTLS_SSL_SOME_MODES_USE_MAC, is not
present in Mbed Crypto.
- Use baremetal config in all.sh, as Mbed Crypto's baremetal
configuration does exclude the net module (as it doesn't exist in Mbed
Crypto)
- Reject cmake_subproject_build changes, continuing to link only
libmbedcrypto.
- Reject changes to visualc and associated templates. Mbed Crypto
doesn't need additional logic to handle submodule-sourced headers.
- Avoid adding fuzzers from Mbed TLS. The only relevant fuzzers are the
privkey and pubkey fuzzers, but non-trivial work would be required to
integrate those into Mbed Crypto (more than is comfortable in a merge
commit).
- Reject addition of Docker wrappers for compat.sh and ssl-opt.sh, as
those are not present in Mbed Crypto.
- Remove calls to SSL-related scripts from basic-in-docker.sh
Fix test errors by performing the following:
- Avoid using a link that Doxygen can't seem to resolve in Mbed Crypto,
but can resolve in Mbed TLS. In documentation for
MBEDTLS_CHECK_PARAMS, don't attempt to link to MBEDTLS_PARAM_FAILED.
* origin/development: (339 commits)
Do not build fuzz on windows
No booleans and import config
Removing space before opening parenthesis
Style corrections
Syntax fix
Fixes warnings from MSVC
Add a linker flag to enable gcov in basic-build-test.sh
Update crypto submodule to a revision with the HAVEGE header changes
Test with MBEDTLS_ECP_RESTARTABLE
Allow TODO in code
Use the docstring in the command line help
Split _abi_compliance_command into smaller functions
Record the commits that were compared
Document how to build the typical argument for -s
Allow running /somewhere/else/path/to/abi_check.py
tests: Limit each log to 10 GiB
Warn if VLAs are used
Remove redundant compiler flag
Consistently spell -Wextra
Fix parsing issue when int parameter is in base 16
...
In the generic message digest abstraction, instead of storing method
pointers in the per-algorithm data structure and using wrapper
functions as those methods, call the per-algorithm function directly.
This saves some code size (2336B -> 2043B for md with all algorithms
enabled on M0+ with gcc -Os). This should also make it easier to
optimize the case when a single algorithm is supported. In addition,
this is a very slight security improvement since it removes one
opportunity for a buffer overflow to directly turn into letting the
attacker overwrite a pointer to a function pointer.
This commit does not modify the documented API. However, it removes
the possibility for users to define their own hash implementations and
use them by building their own md_info.
Changing mbedtls_md_context to contain a md type identifier rather
than a pointer to an info structure would save a few more bytes and a
few more runtime memory accesses, but would be a major API break since
a lot of code uses `const mbedtls_md_info *` to keep track of which
hash is in use.
Increase the SO versions of libmbedx509 and libmbedtls due to the
addition of fields in publicly visible (non-opaque) structs:
- mbedtls_ssl_config
- mbedtls_ssl_context
- mbedtls_x509_crt
Adapt tests in all.sh:
- tests with submodule enabled (default) no longer need to enable it
explicitly, and no longer need runtime tests, as those are now handled by
all other test cases in this script
- tests with submodule disabled (old default) now need to disable it
explicitly, and execute some runtime tests, as those are no longer tested
anywhere else in this script
Adapt documentation in Readme: remove the section "building with submodule"
and replace it with a new section before the other building sections.
Purposefully don't document how to build not from the submodule, as that
option is going away soon.
When running lcov, files can't be found relative to the parent project
(Mbed TLS) root. Use full, non-relative paths to refer to files used in
building Mbed Crypto from Mbed TLS in order to enable lcov to locate the
files properly.
Remove debug print added to print list of source files used in making
libmbedcrypto.
Fixes 92da0bd862 ("Makefile: Use generated source files from parent").
When building as a submodule of a parent project, like Mbed TLS, use the
parent projects generated source files (error.c, version.c,
version_features.c)
Don't depend on the C compiler's default output file name and path. Make
knows what it wants to build and where it should go, and this may not
always align with the C compiler default, so tell the C compilter to
output to the Make target explicitly.
Since the ITS API has stabilized and we don't plan to make use of more
than ITS, we don't need an abstraction layer between key storage and
key storage over ITS. Merge the ITS code into the generic storage
module.
Now that we have ITS over files, we no longer need a direct backend
for key storage over files. Remove psa_crypto_storage_file and its
tests.
Switch MBEDTLS_PSA_CRYPTO_STORAGE_ITS_C and MBEDTLS_PSA_ITS_FILE_C on
by default. This preserves functionality and test coverage in the
default configuration, but forgets any key previously stored using the
file backend.
Resolve conflicts by performing the following.
- Take the upstream Mbed TLS ChangeLog verbatim.
- Reject changes to Makefiles and CMake that are related to using Mbed
Crypto as a submodule. It doesn't make sense to use Mbed Crypto as a
submodule of itself.
- Reject README changes, as Mbed Crypto has its own, different README.
- Reject PSA-related changes to config.h. We don't want to disable the
availability of the PSA Crypto API by default in the Mbed Crypto
config.h.
- Don't inadvertently revert dead code removal in
mbedtls_cipher_write_tag() which was added in f2a7529403 ("Fix
double return statement in cipher.c")
- Where Mbed Crypto already had some MBEDTLS_USE_PSA_CRYPTO code (from
past companion PRs) take the latest version from Mbed TLS which
includes integration with MBEDTLS_CHECK_PARAMS.
- Update the version of the shared library files to match what's
currently present in Mbed TLS.
- Reject removal of testing with PSA from config full tests.
- Resolve conflicts in test tests/suites/helpers.function, where both
Mbed Crypto and Mbed TLS both added documentation for TEST_ASSERT.
Combine text from both documentation efforts.
- Reject adding a submodule of ourselves.
- Reject addition of submodule tests in all.sh.
- Reject addition of submodule to library path in
tests/scripts/run-test-suites.pl.
- Avoid using USE_CRYPTO_SUBMODULE=1 in
component_test_use_psa_crypto_full_cmake_asan() in all.sh.
Implement psa_allocate_key, psa_open_key, psa_create_key,
psa_close_key.
Add support for keys designated to handles to psa_get_key_slot, and
thereby to the whole API.
Allocated and non-allocated keys can coexist. This is a temporary
stage in order to transition from the use of direct slot numbers to
allocated handles only. Once all the tests and sample programs have
been migrated to use handles, the implementation will be simplified
and made more robust with support for handles only.
For Makefiles, enable overriding where includes can come from in order to
enable the parent module to set the include path. This allows the parent
module to specify that its config.h should be used, even when the submodule
when built standalone would use a different config.h.
For CMake, always look in the parent's include folder and our own. List the
parent's include folder first, so that preference is given to parent
include files.
The new file is conditionally compiled with the new mbedtls
configuration option that Mbed OS would set by default -
`MBEDTLS_PSA_CRYPTO_STORAGE_ITS_C`.
-
Add new functions, psa_load_persistent_key(),
psa_free_persistent_key_data(), and psa_save_persistent_key(), for
managing persistent keys. These functions load to or save from our
internal representation of key slots. Serialization is a concern of the
storage backend implementation and doesn't abstraction-leak into the
lifetime management code.
An initial implementation for files is provided. Additional storage
backends can implement this interface for other storage types.
