Botan  1.10.9
dev_random.cpp
Go to the documentation of this file.
1 /*
2 * Reader of /dev/random and company
3 * (C) 1999-2009,2013 Jack Lloyd
4 *
5 * Distributed under the terms of the Botan license
6 */
7 
8 #include <botan/internal/dev_random.h>
9 
10 #include <sys/types.h>
11 #include <sys/select.h>
12 #include <sys/stat.h>
13 #include <unistd.h>
14 #include <fcntl.h>
15 #include <string.h>
16 
17 namespace Botan {
18 
19 namespace {
20 
21 int open_nonblocking(const char* pathname)
22  {
23 #ifndef O_NONBLOCK
24  #define O_NONBLOCK 0
25 #endif
26 
27 #ifndef O_NOCTTY
28  #define O_NOCTTY 0
29 #endif
30 
31  const int flags = O_RDONLY | O_NONBLOCK | O_NOCTTY;
32  return ::open(pathname, flags);
33  }
34 
35 }
36 
37 /**
38 Device_EntropySource constructor
39 Open a file descriptor to each (available) device in fsnames
40 */
41 Device_EntropySource::Device_EntropySource(const std::vector<std::string>& fsnames)
42  {
43  for(size_t i = 0; i != fsnames.size(); ++i)
44  {
45  fd_type fd = open_nonblocking(fsnames[i].c_str());
46  if(fd >= 0 && fd < FD_SETSIZE)
47  devices.push_back(fd);
48  }
49  }
50 
51 /**
52 Device_EntropySource destructor: close all open devices
53 */
55  {
56  for(size_t i = 0; i != devices.size(); ++i)
57  ::close(devices[i]);
58  }
59 
60 /**
61 * Gather entropy from a RNG device
62 */
64  {
65  if(devices.empty())
66  return;
67 
68  const size_t ENTROPY_BITS_PER_BYTE = 8;
69  const size_t MS_WAIT_TIME = 32;
70  const size_t READ_ATTEMPT = accum.desired_remaining_bits() / 4;
71 
72  MemoryRegion<byte>& io_buffer = accum.get_io_buffer(READ_ATTEMPT);
73 
74  int max_fd = devices[0];
75  fd_set read_set;
76  FD_ZERO(&read_set);
77  for(size_t i = 0; i != devices.size(); ++i)
78  {
79  FD_SET(devices[i], &read_set);
80  max_fd = std::max(devices[i], max_fd);
81  }
82 
83  struct ::timeval timeout;
84 
85  timeout.tv_sec = (MS_WAIT_TIME / 1000);
86  timeout.tv_usec = (MS_WAIT_TIME % 1000) * 1000;
87 
88  if(::select(max_fd + 1, &read_set, 0, 0, &timeout) < 0)
89  return;
90 
91  for(size_t i = 0; i != devices.size(); ++i)
92  {
93  if(FD_ISSET(devices[i], &read_set))
94  {
95  const ssize_t got = ::read(devices[i], &io_buffer[0], io_buffer.size());
96  if(got > 0)
97  accum.add(&io_buffer[0], got, ENTROPY_BITS_PER_BYTE);
98  }
99  }
100  }
101 
102 }
Device_EntropySource(const std::vector< std::string > &fsnames)
Definition: dev_random.cpp:41
MemoryRegion< byte > & get_io_buffer(size_t size)
Definition: entropy_src.h:38
void add(const void *bytes, size_t length, double entropy_bits_per_byte)
Definition: entropy_src.h:70
#define O_NONBLOCK
void poll(Entropy_Accumulator &accum)
Definition: dev_random.cpp:63
#define O_NOCTTY
size_t size() const
Definition: secmem.h:29
size_t desired_remaining_bits() const
Definition: entropy_src.h:56