Quickly mention the status of RSA accel
Not related to other commits in this PR, should have been done in #8616
really, but since I'm updating the document, might as well do it here.
Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/docs/driver-only-builds.md b/docs/driver-only-builds.md
index 1a60bfd..8f70825 100644
--- a/docs/driver-only-builds.md
+++ b/docs/driver-only-builds.md
@@ -55,6 +55,8 @@
- hashes: SHA-3, SHA-2, SHA-1, MD5, etc.
- elliptic-curve cryptography (ECC): ECDH, ECDSA, EC J-PAKE, ECC key types.
- finite-field Diffie-Hellman: FFDH algorithm, DH key types.
+- RSA: PKCS#1 v1.5 and v2.1 signature and encryption algorithms, RSA key types
+ (for now, only crypto, no X.509 or TLS support).
- AEADs:
- GCM and CCM with AES, ARIA and Camellia key types
- ChachaPoly with ChaCha20 Key type
@@ -71,9 +73,6 @@
in the "Limitations" sub-sections of the sections dedicated to each family
below.
-Currently (mid-2023) we don't have plans to extend this to RSA. If
-you're interested in driver-only support for RSA, please let us know.
-
Hashes
------
@@ -138,9 +137,10 @@
still be included in the build, see limitations sub-section below.
In addition, if:
-- `MBEDTLS_ECP_C` is fully removed (see limitation sub-section below), and
-- support for RSA key types and algorithms is fully disabled, and
-- support for DH key types and the FFDH algorithm is either disabled, or
+- `MBEDTLS_ECP_C` is fully removed (see limitation sub-section below),
+- and support for RSA key types and algorithms is either fully disabled or
+ fully provided by a driver,
+- and support for DH key types and the FFDH algorithm is either disabled or
fully provided by a driver,
then you can also disable `MBEDTLS_BIGNUM_C`.
@@ -243,6 +243,29 @@
`[PSA_WANT|MBEDTLS_PSA_ACCEL]_ALG_FFDH` allow builds accelerating FFDH and
removing builtin support (i.e. `MBEDTLS_DHM_C`).
+RSA
+---
+
+It is possible for all RSA operations to be provided only by a driver.
+
+More precisely, if:
+- all the RSA algorithms that are enabled (`PSA_WANT_ALG_RSA_*`) are also
+ accelerated (`MBEDTLS_PSA_ACCEL_ALG_RSA_*`),
+- and all the RSA key types that are enabled (`PSA_WANT_KEY_TYPE_RSA_*`) are
+ also accelerated (`MBEDTLS_PSA_ACCEL_KEY_TYPE_RSA_*`),
+
+then you can disable `MBEDTLS_RSA_C`, `MBEDTLS_PKCS1_V15` and
+`MBEDTLS_PKCS1_V21`, and RSA will still work in PSA Crypto.
+
+### Limitations on RSA acceleration
+
+Unlike other mechanisms, for now in configurations with driver-only RSA, only
+PSA Crypto works. In particular, PK, X.509 and TLS will _not_ work with
+driver-only RSA even if `MBEDTLS_USE_PSA_CRYPTO` is enabled.
+
+Currently (early 2024) we don't have plans to extend this support. If you're
+interested in wider driver-only support for RSA, please let us know.
+
Ciphers (unauthenticated and AEAD)
----------------------------------