driver-only-builds: update EC and FFDH sections
Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/docs/driver-only-builds.md b/docs/driver-only-builds.md
index a55bbc5..1a42a3f 100644
--- a/docs/driver-only-builds.md
+++ b/docs/driver-only-builds.md
@@ -76,10 +76,6 @@
Elliptic-curve cryptography (ECC)
---------------------------------
-Note: things are still evolving. This section describes the situation right
-after #7452 has been merged. It will be updated again in #7757 when bignum is
-done.
-
It is possible to have most ECC operations provided only by a driver:
- the ECDH, ECDSA and EC J-PAKE algorithms;
- key import, export, and random generation.
@@ -107,6 +103,11 @@
RSA or FFDH, then you can also disable `MBEDTLS_BIGNUM_C` for further code
size saving.
+[Coming soon] As noted in the "Limitations regarding the selection of curves"
+section below, there is an upcoming requirement for all the required curves to
+be also accelerated in the PSA driver in order to exclude the builtin algs
+support.
+
### Limitations regarding fully removing `ecp.c`
A limited subset of `ecp.c` will still be automatically re-enabled if any of
@@ -144,10 +145,34 @@
### Limitations regarding the selection of curves
-TODO: apparently we don't really support having some curves built-in and
-others driver-only... investigate and describe the situation. See also #7899.
+There is an ongoing work which tries to establish a link/constrain between
+the list of supported curves and supported algorithms both in builtin and PSA
+sides. In particular:
+
+- #8014 ensures that the curves supported on the PSA side (`PSA_WANT_ECC_xxx`)
+ are always a superset of the builtin ones (`MBEDTLS_ECP_DP_xxx`)
+- #8016 forces builtin alg support as soon as there is at least one builtin
+ curve. In other words, in order to exclue all builtin algs, all the required
+ curves should be supported and accelerated by the PSA driver.
Finite-field Diffie-Hellman
---------------------------
-TODO
+Support is pretty similar to the "Elliptic-curve cryptography (ECC)" section
+above.
+Key management and usage can be enabled by means of the usual `PSA_WANT` +
+`MBEDTLS_PSA_ACCEL` pairs:
+
+- `[PSA_WANT|MBEDTLS_PSA_ACCEL]_KEY_TYPE_DH_PUBLIC_KEY`;
+- `[PSA_WANT|MBEDTLS_PSA_ACCEL]_KEY_TYPE_DH_KEY_PAIR_BASIC`;
+- `[PSA_WANT|MBEDTLS_PSA_ACCEL]_KEY_TYPE_DH_KEY_PAIR_IMPORT`;
+- `[PSA_WANT|MBEDTLS_PSA_ACCEL]_KEY_TYPE_DH_KEY_PAIR_EXPORT`;
+- `[PSA_WANT|MBEDTLS_PSA_ACCEL]_KEY_TYPE_DH_KEY_PAIR_GENERATE`;
+
+The same holds for the associated algorithm:
+`[PSA_WANT|MBEDTLS_PSA_ACCEL]_ALG_FFDH` allow to build accelerating FFDH and
+removing builtin support (i.e. `MBEDTLS_DHM_C`).
+
+### Limitations
+Support for deterministic derivation of a DH keypair
+(i.e. `PSA_WANT_KEY_TYPE_RSA_KEY_PAIR_DERIVE`) is not supported.