commit 654bef0be087a0cd5841fef9b3699d91275c85a5
author Przemek Stekiel <przemyslaw.stekiel@mobica.com> Thu Dec 15 13:28:02 2022 +0100
committer Przemek Stekiel <przemyslaw.stekiel@mobica.com> Wed Apr 26 09:07:20 2023 +0200
tree a36a291af0793384938bcf8fddf0f08ab6b936a4
parent 87d9a4a30c9aa915c900abc31a580173b48fcd62

Fix typos, comments, style, optimize macros

Signed-off-by: Przemek Stekiel <przemyslaw.stekiel@mobica.com>

library/Makefile

diff --git a/library/Makefile b/library/Makefile
index 5c4471e..51e7a15 100644
--- a/library/Makefile
+++ b/library/Makefile
@@ -134,7 +134,7 @@
 	     psa_crypto_client.o \
 	     psa_crypto_driver_wrappers.o \
 	     psa_crypto_ecp.o \
-		 psa_crypto_ffdh.o \
+	     psa_crypto_ffdh.o \
 	     psa_crypto_hash.o \
 	     psa_crypto_mac.o \
 	     psa_crypto_pake.o \

library/psa_crypto_ffdh.c

diff --git a/library/psa_crypto_ffdh.c b/library/psa_crypto_ffdh.c
index 6b07a7d..1e76d13 100644
--- a/library/psa_crypto_ffdh.c
+++ b/library/psa_crypto_ffdh.c
@@ -149,7 +149,7 @@
         MBEDTLS_MPI_CHK(mbedtls_mpi_read_binary(&GY, peer_key,
                                                 peer_key_length));
 
-        /* Calculate shared secret public key: K = G^(XY) mod P */
+        /* Calculate shared secret public key: K = G^(XY) mod P = GY^X mod P */
         MBEDTLS_MPI_CHK(mbedtls_mpi_exp_mod(&K, &GY, &X, &P, NULL));
 
         MBEDTLS_MPI_CHK(mbedtls_mpi_write_binary(&K, shared_secret,
@@ -221,6 +221,9 @@
         PSA_BITS_TO_BYTES(attributes->core.bits), &P, NULL);
 
     if (status == PSA_SUCCESS) {
+        /* RFC7919: Traditional finite field Diffie-Hellman has each peer choose their
+           secret exponent from the range [2, P-2].
+           Select random value in range [4, P] and decrease it by 2. */
         MBEDTLS_MPI_CHK(mbedtls_mpi_random(&X, 4, &P, mbedtls_psa_get_random,
                                            MBEDTLS_PSA_RANDOM_STATE));
         MBEDTLS_MPI_CHK(mbedtls_mpi_sub_int(&X, &X, 2));