Legacy-PSA bridge design: symmetric #8769
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Signed-off-by: Gilles Peskine <[email protected]>
Signed-off-by: Gilles Peskine <[email protected]>
Signed-off-by: Gilles Peskine <[email protected]>
Signed-off-by: Gilles Peskine <[email protected]>
gilles-peskine-arm
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Sorry for picking on names, but if it's about symmetric crypto it's hardly about PK, but rather legacy-PSA? |
gilles-peskine-arm
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Er, yeah, too much copy-paste. Too late for the branch name but I've changed the title. |
mpg
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Feb 7, 2024
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| Applications transitioning to the PSA API may wish to take advantage of PSA accelerated ciphers or opaque keys, while still constrained to provide the legacy `cipher.h` interface. | ||
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| Mbed TLS 3.5 offers `mbedtls_cipher_setup_psa()` for this transition. |
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Notes about this function:
- it's marked as deprecated;
- it only works for a limited number of ciphers / mechanisms : only AES with GCM, CCM, CCM*, CBC, ECB;
- it doesn't when AES is driver-only (it should take advantage of a driver when present, tough, probably just won't work unless
AES_Cis also defined because sorting out the dependencies for this was not a priority considering this function is deprecated).
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Do you think we can reasonably lift these limitations in 3.6.x if there's demand?
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Sure, I don't foresee any problem here. The main reason it wasn't done is it didn't look like a priority.
| * We do not seem to need this much in our own code. TLS has its own conversion, limited to the subset of mechanisms that it uses. | ||
| * The [“Symmetric encryption” section of the transition guide](../../psa-transition.md#symmetric-encryption) does not demonstrate the need for applications to write complex code to bridge the gap, the way it does with asymmetric crytography in Mbed TLS 3.5. However, there is arguably an omission there, since the transition guide does not show how to translate metadata. | ||
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| [OPEN] Do we need conversion functions between encodings of cipher mechanisms? |
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I'm weakly inclined to say no. OTOH, those would be rather easy to provide. Also, I'll note we could easily add those in 3.6.x if requested.
valeriosetti
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For the open points, we're currently planning no action, so I don't think we need issues. |
valeriosetti
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Feb 8, 2024
mpg
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Mbed-TLS:dev/gilles-peskine-arm/pk-psa-bridge-design
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Document requirements for bridging legacy APIs and PSA APIs. The scope of this pull request is symmetric crytography (cipher/AEAD, MAC, key derivation, random generation). Together with #8657, it represents all the classes of cryptographic mechanisms that exist in some form in both APIs.
Follow-up to #8657, to be rebased once that is merged.
PR checklist
Please tick as appropriate and edit the reasons (e.g.: "backport: not needed because this is a new feature")