Mbed-TLS
Document lack of API stability for the cipher module in 4.0
We have decided to keep the cipher module in 4.0 but as an internal API that doesn't have API stability guarantees and therefore can be changed or removed in a minor version.
The header will be made internal as part of the repo-split, but it is best to document this fact clearly and say explicitly.
NIST KW and XTS are not available in PSA yet and need to be moved to a separate public header.
I think this is mostly covered by https://github.com/Mbed-TLS/mbedtls/issues/10087 and https://github.com/Mbed-TLS/TF-PSA-Crypto/issues/220 - at least the part mentioned in the title.
Regarding the details:
- NIST-KW is handled by https://github.com/Mbed-TLS/TF-PSA-Crypto/pull/180
- XTS I'm not sure - it doesn't seem to be really available in PSA yet (the only hits in tests are in the metadata test suite), is this a temporary regression we've accepted by making cipher private? Or should we make a subset of cipher public just for XTS?
@yanesca @gilles-peskine-arm wdyt?
My first thought would be to split out the xts part of aes.h and make that public. On a quick look it looks relatively standalone and it feels simpler/more direct than through cipher.
We aren't going to do any coding work for this before 1.0.
XTS is one of the things that we've agreed to sacrified in 1.0.
I think this task does need to remain open, but solely as a documentation task, mostly on the migration guide.
This has been done. cipher.h is no longer a public header, it has now been moved to a private subdirectory of the include path.