From e16029027dfdf506566994697138f14cd6dcebd5 Mon Sep 17 00:00:00 2001
From: Tennessee Carmel-Veilleux <tennessee.carmelveilleux@gmail.com>
Date: Wed, 13 Oct 2021 12:17:36 -0400
Subject: [PATCH] Introduce a RNG determinism audit

- Add a temporary audit function in ExchangeMgr.cpp.
- ExchangeMgr.cpp is used because it is used by both
  `DeviceController` and `Server` (i.e. by all modalities)
  and it already relies on random numbers.
- Audit must be run manually since it needs to be done on targets
  and comparisons across reboot.
- Audit validates `GetRandU*` and `Crypto::DRBG_get_bytes()`,
  which may both use different underlying impl.

Testing done:

- Unit tests pass
- Manually tested on Linux by commenting-out `srand(seed);` in
  Entropy.cpp, which forces `GetRandU*` to give the same values
  across calls.
- If you are testing this, search for lines starting with `AUDIT:`
  in the log.

Issue #10454
---
 src/messaging/ExchangeMgr.cpp | 55 +++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/src/messaging/ExchangeMgr.cpp b/src/messaging/ExchangeMgr.cpp
index 6cd46ac7baef51..749a4bdb9616e1 100644
--- a/src/messaging/ExchangeMgr.cpp
+++ b/src/messaging/ExchangeMgr.cpp
@@ -33,6 +33,13 @@
 #include <inttypes.h>
 #include <stddef.h>
 
+// Temporary includes for TemporaryAuditRandomPerformance()
+// TODO: remove once https://github.com/project-chip/connectedhomeip/issues/10454 is done.
+#if 1
+#include <crypto/CHIPCryptoPAL.h>
+#include <lib/support/BytesToHex.h>
+#endif
+
 #include <lib/core/CHIPCore.h>
 #include <lib/core/CHIPEncoding.h>
 #include <lib/support/CHIPFaultInjection.h>
@@ -50,6 +57,49 @@ using namespace chip::System;
 namespace chip {
 namespace Messaging {
 
+namespace {
+
+// Audit random number generator proper initialization with prints.
+// TODO: remove once https://github.com/project-chip/connectedhomeip/issues/10454 is done.
+void TemporaryAuditRandomNumberGenerator()
+{
+    uint8_t buf1[16];
+    uint8_t buf2[16];
+
+    memset(&buf1[0], 0, sizeof(buf1));
+    memset(&buf2[0], 0, sizeof(buf2));
+
+    VerifyOrDie(chip::Crypto::DRBG_get_bytes(&buf1[0], sizeof(buf1)) == CHIP_NO_ERROR);
+    VerifyOrDie(chip::Crypto::DRBG_get_bytes(&buf2[0], sizeof(buf2)) == CHIP_NO_ERROR);
+
+    char hex_buf[sizeof(buf1) * 2 + 1];
+
+    ChipLogProgress(ExchangeManager, "AUDIT: ===== RANDOM NUMBER GENERATOR AUDIT START ====");
+    ChipLogProgress(ExchangeManager, "AUDIT: * Validate buf1 and buf2 are <<<different every run/boot!>>>");
+    ChipLogProgress(ExchangeManager, "AUDIT: * Validate r1 and r2 are <<<different every run/boot!>>>");
+
+    memset(&hex_buf[0], 0, sizeof(hex_buf));
+    VerifyOrDie(Encoding::BytesToUppercaseHexString(&buf1[0], sizeof(buf1), &hex_buf[0], sizeof(hex_buf)) == CHIP_NO_ERROR);
+    ChipLogProgress(ExchangeManager, "AUDIT: * buf1: %s", &hex_buf[0]);
+
+    memset(&hex_buf[0], 0, sizeof(hex_buf));
+    VerifyOrDie(Encoding::BytesToUppercaseHexString(&buf2[0], sizeof(buf2), &hex_buf[0], sizeof(hex_buf)) == CHIP_NO_ERROR);
+    ChipLogProgress(ExchangeManager, "AUDIT: * buf2: %s", &hex_buf[0]);
+
+    VerifyOrDieWithMsg(memcmp(&buf1[0], &buf2[0], sizeof(buf1)) != 0, ExchangeManager,
+                       "AUDIT: FAILED: buf1, buf2 are equal: DRBG_get_bytes() does not function!");
+
+    uint32_t r1 = GetRandU32();
+    uint32_t r2 = GetRandU32();
+
+    ChipLogProgress(ExchangeManager, "AUDIT: * r1: 0x%08" PRIX32 " r2: 0x%08" PRIX32, r1, r2);
+    VerifyOrDieWithMsg(r1 != r2, ExchangeManager,
+                       "AUDIT: FAILED: buf1, buf2 are equal: random number generator does not function!");
+    ChipLogProgress(ExchangeManager, "AUDIT: ===== RANDOM NUMBER GENERATOR AUDIT END ====");
+}
+
+} // namespace
+
 /**
  *  Constructor for the ExchangeManager class.
  *  It sets the state to kState_NotInitialized.
@@ -72,6 +122,11 @@ CHIP_ERROR ExchangeManager::Init(SessionManager * sessionManager)
 
     mSessionManager = sessionManager;
 
+    {
+        // TODO: remove once https://github.com/project-chip/connectedhomeip/issues/10454 is done.
+        TemporaryAuditRandomNumberGenerator();
+    }
+
     mNextExchangeId = GetRandU16();
     mNextKeyId      = 0;