basic functionalty

modules/Crypto/Random/OSRNG/rng_base.py

@@ -0,0 +1,88 @@
+#
+#  Random/OSRNG/rng_base.py : Base class for OSRNG
+#
+# Written in 2008 by Dwayne C. Litzenberger <dlitz@dlitz.net>
+#
+# ===================================================================
+# The contents of this file are dedicated to the public domain.  To
+# the extent that dedication to the public domain is not available,
+# everyone is granted a worldwide, perpetual, royalty-free,
+# non-exclusive license to exercise all rights associated with the
+# contents of this file for any purpose whatsoever.
+# No rights are reserved.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+# ===================================================================
+
+__revision__ = "$Id$"
+
+import sys
+if sys.version_info[0] == 2 and sys.version_info[1] == 1:
+    from Crypto.Util.py21compat import *
+
+class BaseRNG(object):
+
+    def __init__(self):
+        self.closed = False
+        self._selftest()
+
+    def __del__(self):
+        self.close()
+
+    def _selftest(self):
+        # Test that urandom can return data
+        data = self.read(16)
+        if len(data) != 16:
+            raise AssertionError("read truncated")
+
+        # Test that we get different data every time (if we don't, the RNG is
+        # probably malfunctioning)
+        data2 = self.read(16)
+        if data == data2:
+            raise AssertionError("OS RNG returned duplicate data")
+
+    # PEP 343: Support for the "with" statement
+    def __enter__(self):
+        pass
+    def __exit__(self):
+        """PEP 343 support"""
+        self.close()
+
+    def close(self):
+        if not self.closed:
+            self._close()
+        self.closed = True
+
+    def flush(self):
+        pass
+
+    def read(self, N=-1):
+        """Return N bytes from the RNG."""
+        if self.closed:
+            raise ValueError("I/O operation on closed file")
+        if not isinstance(N, (long, int)):
+            raise TypeError("an integer is required")
+        if N < 0:
+            raise ValueError("cannot read to end of infinite stream")
+        elif N == 0:
+            return ""
+        data = self._read(N)
+        if len(data) != N:
+            raise AssertionError("%s produced truncated output (requested %d, got %d)" % (self.name, N, len(data)))
+        return data
+
+    def _close(self):
+        raise NotImplementedError("child class must implement this")
+
+    def _read(self, N):
+        raise NotImplementedError("child class must implement this")
+
+
+# vim:set ts=4 sw=4 sts=4 expandtab: