commit cf0156f3f3d89f1c7424a70569199557aa326b05
author Przemek Stekiel <przemyslaw.stekiel@mobica.com> Thu Apr 27 11:12:39 2023 +0200
committer Przemek Stekiel <przemyslaw.stekiel@mobica.com> Thu Apr 27 11:12:39 2023 +0200
tree abcf4af7766a647e2d120f7b618e753017061416
parent 6fd72b687fa70778908a898b6a20c61291755f2a

mbedtls_psa_ffdh_generate_key: Fix random number generation

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

library/psa_crypto_ffdh.c

diff --git a/library/psa_crypto_ffdh.c b/library/psa_crypto_ffdh.c
index b6a9bf4..77d51d5 100644
--- a/library/psa_crypto_ffdh.c
+++ b/library/psa_crypto_ffdh.c
@@ -232,10 +232,10 @@
     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,
+           Select random value in range [3, P-1] and decrease it by 1. */
+        MBEDTLS_MPI_CHK(mbedtls_mpi_random(&X, 3, &P, mbedtls_psa_get_random,
                                            MBEDTLS_PSA_RANDOM_STATE));
-        MBEDTLS_MPI_CHK(mbedtls_mpi_sub_int(&X, &X, 2));
+        MBEDTLS_MPI_CHK(mbedtls_mpi_sub_int(&X, &X, 1));
 
         *key_buffer_length = mbedtls_mpi_size(&X);