commit 81edb0d3347ec35fa7a3a044a5c5359402b0e91c
author Ningyuan Wang <nywang@google.com> Fri Jan 29 15:57:42 2016 -0800
committer Ningyuan Wang <nywang@google.com> Tue Feb 02 21:35:20 2016 +0000
tree ce27afda8c94db87270a29b4b3c923fb4f970993
parent 57c5f54dae6f34e5569e6e343a7793f7db365deb

DHCPV4: use c++11 random number generator

This uses c++11 random number generator to replace the old
c-style random number generator.
In addition, this deletes the function DHCPMessage::
GenerateTransactionID(). Both the DHCP transaction id and
IP transaction id will be generated by the random engine in
DHCPV4.

Bug: 25642025
TEST=compile and unittest

Change-Id: Ie23600f08f5dab8b373bf19eac7b25c112e1a1c8

dhcp_message.cc

diff --git a/dhcp_message.cc b/dhcp_message.cc
index b1c83e6..7b9a8b2 100644
--- a/dhcp_message.cc
+++ b/dhcp_message.cc
@@ -376,12 +376,6 @@
   return ~static_cast<uint16_t>(sum);
 }
 
-uint32_t DHCPMessage::GenerateTransactionID() {
-  // TODO(nywang): use arc4 random number for better security.
-  srand(time(NULL));
-  return rand() % UINT32_MAX;
-}
-
 void DHCPMessage::SetClientIdentifier(
     const ByteString& client_identifier) {
   client_identifier_ = client_identifier;

dhcp_message.h

diff --git a/dhcp_message.h b/dhcp_message.h
index 3b0a852..39b3929 100644
--- a/dhcp_message.h
+++ b/dhcp_message.h
@@ -60,7 +60,6 @@
                              DHCPMessage* message);
   static DHCPMessage InitRequest();
   static uint16_t ComputeChecksum(const uint8_t* data, size_t len);
-  static uint32_t GenerateTransactionID();
   // Initialize part of the data fields for outbound DHCP message.
   // Serialize the message to a buffer
   bool Serialize(shill::ByteString* data) const;

dhcpv4.cc

diff --git a/dhcpv4.cc b/dhcpv4.cc
index 016d75f..3ef58ed 100644
--- a/dhcpv4.cc
+++ b/dhcpv4.cc
@@ -24,6 +24,8 @@
 #include <netinet/ip.h>
 #include <netinet/udp.h>
 
+#include <random>
+
 #include <base/bind.h>
 #include <base/logging.h>
 
@@ -86,7 +88,8 @@
       from_(INADDR_ANY),
       to_(INADDR_BROADCAST),
       socket_(kInvalidSocketDescriptor),
-      sockets_(new shill::Sockets()) {
+      sockets_(new shill::Sockets()),
+      random_engine_(time(nullptr)) {
 }
 
 DHCPV4::~DHCPV4() {
@@ -266,8 +269,9 @@
   // so fragmentation is not needed.
   ip->frag_off = 0;
   // Identification.
-  // TODO(nywang) Use arc4 random number.
-  ip->id = static_cast<uint16_t>(rand());
+  ip->id = static_cast<uint16_t>(
+      std::uniform_int_distribution<unsigned int>()(
+          random_engine_) % UINT16_MAX + 1);
   // Time to live.
   ip->ttl = IPDEFTTL;
   // Total length.

dhcpv4.h

diff --git a/dhcpv4.h b/dhcpv4.h
index c1ea166..ebe2f5a 100644
--- a/dhcpv4.h
+++ b/dhcpv4.h
@@ -17,6 +17,7 @@
 #ifndef DHCP_CLIENT_DHCPV4_H_
 #define DHCP_CLIENT_DHCPV4_H_
 
+#include <random>
 #include <string>
 
 #include <base/macros.h>
@@ -94,6 +95,8 @@
   // Helper class with wrapped socket relavent functions.
   std::unique_ptr<shill::Sockets> sockets_;
 
+  std::default_random_engine random_engine_;
+
   DISALLOW_COPY_AND_ASSIGN(DHCPV4);
 };