ECP keypair utility functions #7815

gilles-peskine-arm · 2023-06-21T18:46:04Z

Add utility functions to the ECP module to query and construct key pairs and points. This replaces the direct access to mbedtls_ecp_keypair and mbedtls_ecp_point fields that was possible in Mbed TLS 2.x. Fixes #5441, fixes #8367, fixes #8652.

Update the sample programs. They now no longer do any direct access to private fields of mbedtls_ecp_keypair or mbedtls_ecp_point. Fixes #5017. Note that any unrelated improvement of sample programs or their testing is out of scope here. I used the following to test them:

run programs/pkey/ecdsa
run smoke.sh secp256r1 && smoke.sh x25519 using smoke.sh.txt

Follow-up: use the new functions to simplify the PSA transition guide.

PR checklist

Please tick as appropriate and edit the reasons (e.g.: "backport: not needed because this is a new feature")

changelog provided
backport no (new feature)
tests provided

tests/suites/test_suite_ecp.function

tom-cosgrove-arm · 2023-07-24T14:11:31Z

This increases code size by 200 bytes when compiled for TF-M (their config, P-256 only, no programs/ used) with ArmClang 6.19 with -Oz

orig:5647d06be	pr:7815:1c8f9d61d	Delta	Filename
6464, 0	6664, 0	+200+0	`ecp.o`

include/mbedtls/ecp.h

mpg

Only a design review for now. I'm mostly happy except for export_coordinates() where I disagree with the current API and am not convinced we really need it at all (but not opposed to adding it either).

include/mbedtls/ecp.h

ChangeLog.d/ecp-keypair-utilities.txt

include/mbedtls/ecp.h

tests/suites/test_suite_ecp.function

ChangeLog.d/ecp-keypair-utilities.txt

Add a simple function to get the group id from a key object. This information is available via mbedtls_ecp_export, but that function consumes a lot of memory, which is a waste if all you need is to identify the curve. Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

Sometimes you don't need to have all the parts of a key pair object. Relax the behavior of mbedtls_ecp_keypair so that you can extract just the parts that you need. Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

gilles-peskine-arm · 2023-12-24T18:54:16Z

I've pushed a new history that never creates mbedtls_ecp_point_export_coordinates. The actual development history, with that function added and removed and with some commits to fix minor issues based on CI or review feedback, but rebased midway on top of a recent development to avoid merge conflicts, is in https://github.com/gilles-peskine-arm/mbedtls/tree/ecp-export-partial-4.

mpg

Looking pretty good, just a few minor things and a couple of questions.

include/mbedtls/ecp.h

programs/pkey/gen_key.c

include/mbedtls/ecp.h

programs/pkey/gen_key.c

tests/suites/test_suite_ecp.data

tests/suites/test_suite_ecp.function

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

mpg

Looking good, apart from the superfluous BIGNUM_C guards that I'd like removed.

mpg · 2024-01-03T11:45:07Z

I'm removing "needs-design-approval" as I think we know have an agreement on the design.

All of ECP requires the bignum module and there is no plan to change that, so guarding a few bits of code is just noise. Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

mpg

LGTM

minosgalanakis

Looks good overall.

Two notes:

I assume that the setter for public key mbedtls_ecp_read_public_key is intentionally missing?

If a user needs to importa public key they should import the private one using mbedtls_ecp_read_key () and then calculate the public using mbedtls_ecp_keypair_calc_public() ?
The show_ecp_key(const mbedtls_ecp_keypair *ecp, int has_private) method could be either a helper function for programs or even an API call? Given the complexity to produce a readable printout, we should at least point the users to how to do it.

The latter is not a strong ask, and should not block this PR.

gilles-peskine-arm · 2024-01-16T16:36:46Z

I assume that the setter for public key mbedtls_ecp_read_public_key is intentionally missing?

I'm not sure what that would be. How would it differ from mbedtls_ecp_set_public_key?

The show_ecp_key(const mbedtls_ecp_keypair *ecp, int has_private) method could be either a helper function for programs

It could be, but those programs are currently self-contained. They're sample programs, so there's a strong argument that people should be able to just take the one .c file and modify it. That's a high barrier for introducing a new dependency. Conversely, this is code that we rarely modify, so the cost of duplication is low. So this is a rare case where I think code duplication is ok, even if we didn't have time constraints.

or even an API call? Given the complexity to produce a readable printout, we should at least point the users to how to do it.

Printing out keys in a readable format is rarely done apart from demos. So it doesn't belong in the API, and I don't think we need to call it out in documentation.

minosgalanakis

LGTM

gilles-peskine-arm added needs-work needs-design-approval component-crypto Crypto primitives and low-level interfaces needs-ci Needs to pass CI tests size-s Estimated task size: small (~2d) priority-medium Medium priority - this can be reviewed as time permits labels Jun 21, 2023

mpg self-requested a review June 22, 2023 07:27

gilles-peskine-arm force-pushed the ecp-export-partial branch from c7d878d to 895fbf6 Compare June 22, 2023 18:37

gilles-peskine-arm commented Jun 22, 2023

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gilles-peskine-arm added needs-review Every commit must be reviewed by at least two team members, needs-reviewer This PR needs someone to pick it up for review and removed needs-work needs-ci Needs to pass CI tests labels Jun 26, 2023

gilles-peskine-arm mentioned this pull request Jul 26, 2023

Enable DH in generate_psa_tests.py #7909

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gilles-peskine-arm mentioned this pull request Oct 16, 2023

Add accessor (getter/setter) function for mbedtls_ecp_keypair #8367

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minosgalanakis added priority-high High priority - will be reviewed soon and removed priority-medium Medium priority - this can be reviewed as time permits labels Nov 13, 2023

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Review requested MBEDTLS_PRIVATE accessors. #8529

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gilles-peskine-arm commented Nov 27, 2023

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daverodgman self-requested a review November 27, 2023 15:15

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Make bignum non-public #8155

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gilles-peskine-arm added 2 commits December 22, 2023 21:30

Support partial export from mbedtls_ecp_keypair

ba5b5d6

Sometimes you don't need to have all the parts of a key pair object. Relax the behavior of mbedtls_ecp_keypair so that you can extract just the parts that you need. Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

gilles-peskine-arm added 2 commits December 24, 2023 19:51

Add ECP-heavy-only test cases to the driver parity analysis ignore list

3b17ae7

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

Changelog entry for the new ECP functions

28e9d86

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

gilles-peskine-arm force-pushed the ecp-export-partial branch from 13ef596 to 28e9d86 Compare December 24, 2023 18:52

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gilles-peskine-arm added 2 commits January 2, 2024 17:56

Make input parameter const

39b7bba

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

Improve readability of null-argument tests

5d86787

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

mpg reviewed Jan 3, 2024

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mpg removed the needs-design-approval label Jan 3, 2024

Remove useless guards on MBEDTLS_BIGNUM_C

a10d112

All of ECP requires the bignum module and there is no plan to change that, so guarding a few bits of code is just noise. Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

gilles-peskine-arm requested a review from mpg January 3, 2024 13:09

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minosgalanakis added approved Design and code approved - may be waiting for CI or backports and removed needs-review Every commit must be reviewed by at least two team members, labels Jan 17, 2024

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Merged via the queue into Mbed-TLS:development with commit b1f96c0 Jan 18, 2024
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gilles-peskine-arm mentioned this pull request Jan 25, 2024

Option to export single component from ecp structure #8746

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gilles-peskine-arm mentioned this pull request Feb 12, 2024

Cannot anymore load public key into a ecp_keypair in v3.0 #6833

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ECP keypair utility functions #7815

ECP keypair utility functions #7815

gilles-peskine-arm commented Jun 21, 2023 •

edited by mpg

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ECP keypair utility functions #7815

ECP keypair utility functions #7815

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