Add PRNG reading from /dev/urandom

[Keegan: various small changes]

src/crypto/Makefile.am

@@ -10,5 +10,6 @@ libmoshcrypto_a_SOURCES = \
 	crypto.cc \
 	crypto.h \
 	ocb.cc \
+	prng.h \
 	rijndael-alg-fst.cc \
 	rijndael-alg-fst.h

src/crypto/prng.h

@@ -0,0 +1,77 @@
+/*
+    Mosh: the mobile shell
+    Copyright 2012 Keith Winstein
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef PRNG_HPP
+#define PRNG_HPP
+
+#include <string>
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+#include <stdint.h>
+
+#include "crypto.h"
+
+/* Read random bytes from /dev/urandom.
+
+   We rely on stdio buffering for efficiency. */
+
+static const char rdev[] = "/dev/urandom";
+
+using namespace Crypto;
+
+class PRNG {
+ private:
+  FILE *randfile;
+
+  /* unimplemented to satisfy -Weffc++ */
+  PRNG( const PRNG & );
+  PRNG & operator=( const PRNG & );
+
+ public:
+  PRNG() : randfile( fopen( rdev, "rb" ) )
+  {
+    if ( randfile == NULL ) {
+      throw CryptoException( std::string( rdev ) + ": " + strerror( errno ) );
+    }
+  }
+
+  ~PRNG() {
+    if ( 0 != fclose( randfile ) ) {
+      throw CryptoException( std::string( rdev ) + ": " + strerror( errno ) );
+    }
+  }
+
+  void fill( void *dest, size_t size ) {
+    if ( 0 == size ) {
+      return;
+    }
+
+    if ( 1 != fread( dest, size, 1, randfile ) ) {
+      throw CryptoException( "Could not read from " + std::string( rdev ) );
+    }
+  }
+
+  uint8_t uint8() {
+    uint8_t x;
+    fill( &x, 1 );
+    return x;
+  }
+};
+
+#endif