From a132beb750ada440172804b98ba49c31b932bc9a Mon Sep 17 00:00:00 2001
From: Gilles Peskine <Gilles.Peskine@arm.com>
Date: Fri, 25 Feb 2022 19:20:36 +0100
Subject: [PATCH] Minimal TLS configuration: documentation improvements

Some of the options have been moved around, but there are no semantic
changes.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
---
 configs/config-ccm-psk-tls1_2.h | 46 ++++++++++++++++++---------------
 1 file changed, 25 insertions(+), 21 deletions(-)

diff --git a/configs/config-ccm-psk-tls1_2.h b/configs/config-ccm-psk-tls1_2.h
index cbebf8c00..0e8f570b2 100644
--- a/configs/config-ccm-psk-tls1_2.h
+++ b/configs/config-ccm-psk-tls1_2.h
@@ -21,11 +21,15 @@
  */
 /*
  * Minimal configuration for TLS 1.2 with PSK and AES-CCM ciphersuites
+ *
  * Distinguishing features:
- * - no bignum, no PK, no X509
- * - fully modern and secure (provided the pre-shared keys have high entropy)
- * - very low record overhead with CCM-8
- * - optimized for low RAM usage
+ * - Optimized for small code size, low bandwidth (on a reliable network),
+ *   and low RAM usage.
+ * - No asymmetric cryptography (no certificates, no Diffie-Hellman key
+ *   exchange).
+ * - Fully modern and secure (provided the pre-shared keys are generated and
+ *   stored securely).
+ * - Very low record overhead with CCM-8.
  *
  * See README.txt for usage instructions.
  */
@@ -36,11 +40,7 @@
 //#define MBEDTLS_HAVE_TIME /* Optionally used in Hello messages */
 /* Other MBEDTLS_HAVE_XXX flags irrelevant for this configuration */
 
-/* mbed TLS feature support */
-#define MBEDTLS_KEY_EXCHANGE_PSK_ENABLED
-#define MBEDTLS_SSL_PROTO_TLS1_2
-
-/* mbed TLS modules */
+/* Mbed TLS modules */
 #define MBEDTLS_AES_C
 #define MBEDTLS_CCM_C
 #define MBEDTLS_CIPHER_C
@@ -53,18 +53,9 @@
 #define MBEDTLS_SSL_SRV_C
 #define MBEDTLS_SSL_TLS_C
 
-/* Save RAM at the expense of ROM */
-#define MBEDTLS_AES_ROM_TABLES
-
-/* Save some RAM by adjusting to your exact needs */
-#define MBEDTLS_PSK_MAX_LEN    16 /* 128-bits keys are generally enough */
-
-/*
- * You should adjust this to the exact number of sources you're using: default
- * is the "platform_entropy_poll" source, but you may want to add other ones
- * Minimum is 2 for the entropy test suite.
- */
-#define MBEDTLS_ENTROPY_MAX_SOURCES 2
+/* TLS protocol feature support */
+#define MBEDTLS_KEY_EXCHANGE_PSK_ENABLED
+#define MBEDTLS_SSL_PROTO_TLS1_2
 
 /*
  * Use only CCM_8 ciphersuites, and
@@ -81,6 +72,19 @@
  */
 #define MBEDTLS_SSL_MAX_CONTENT_LEN             1024
 
+/* Save RAM at the expense of ROM */
+#define MBEDTLS_AES_ROM_TABLES
+
+/* Save some RAM by adjusting to your exact needs */
+#define MBEDTLS_PSK_MAX_LEN    16 /* 128-bits keys are generally enough */
+
+/*
+ * You should adjust this to the exact number of sources you're using: default
+ * is the "platform_entropy_poll" source, but you may want to add other ones
+ * Minimum is 2 for the entropy test suite.
+ */
+#define MBEDTLS_ENTROPY_MAX_SOURCES 2
+
 /* These defines are present so that the config modifying scripts can enable
  * them during tests/scripts/test-ref-configs.pl */
 //#define MBEDTLS_USE_PSA_CRYPTO