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Conversion function from ecp group to PSA curve #7764
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Independent proposal
Info proposalAdd Annoyingly, Common questionsIf a curve is supported in the legacy API but not in the PSA API, should the conversion return the correct result or a not-supported indicator? |
Resolves Mbed-TLS#7764. The PSA and ECP sizes are the same, except for Curve25519 where the ECP size is 256 rather than 255 even though private values are 255-bit numbers. Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
We actually already have these conversions functions. I somehow missed them when I was writing the document. They're I'm not sure they are the API I want for the 3.x/4.x transition period. I was looking at how to integrate this more into the ECP module, and the So I think I want to design new, clean functions, well in time for the 3.x LTS so that we can remove the existing functions. |
@mpg notes that this is a good fit for users who want this functionality because they're doing fancy things with the ECP module. But it's not a good fit for users who are merely using Though I still think the sloppy case of |
Now that we have support for driver-only ECC, I'm strongly inclined against the I agree about removing the sloppy case of |
Btw, should these functions really be declared in I think (See Frank's comment on a related issue: #8340 (comment)) |
Moving of
Am I missing something? |
Sounds right to me! |
Quoting from the document added by #8657:
|
There should be a simple way to convert from a
mbedtls_ecp_group
ormbedtls_ecp_group_id
to the corresponding PSA encoding (curve and bit-size). This is needed when migrating code that needs low-levelecp.h
code to create a key, which is then used through the PSA API. For example, to import a compressed point usingmbedtls_ecp_point_read_binary
followed bymbedtls_ecp_point_write_binary
andpsa_import_key
.Goals of this issue:
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