add entropy module

2 files changed, 96 insertions, 0 deletions

diff --git a/dns/__init__.py b/dns/__init__.py
index ff94406..2d4cfd7 100644
--- a/dns/__init__.py
+++ b/dns/__init__.py
@@ -18,6 +18,7 @@
 __all__ = [
     'dnssec',
     'e164',
+    'entropy',
     'exception',
     'flags',
     'inet',
diff --git a/dns/entropy.py b/dns/entropy.py
new file mode 100644
index 0000000..a73e5e3
--- /dev/null
+++ b/dns/entropy.py
@@ -0,0 +1,95 @@
+# Copyright (C) 2008 Nominum, Inc.
+#
+# Permission to use, copy, modify, and distribute this software and its
+# documentation for any purpose with or without fee is hereby granted,
+# provided that the above copyright notice and this permission notice
+# appear in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND NOMINUM DISCLAIMS ALL WARRANTIES
+# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL NOMINUM BE LIABLE FOR
+# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
+# OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+import time
+
+class EntropyPool(object):
+    def __init__(self, seed=None):
+        self.pool_index = 0
+        self.digest = None
+        self.next_byte = 0
+        if seed is None:
+            try:
+                r = file('/dev/random')
+                try:
+                    seed = r.read(16)
+                finally:
+                    r.close()
+            except:
+                seed = str(time.time())
+        try:
+            import hashlib
+            self.hash = hashlib.sha1()
+            self.hash_len = 20
+        except:
+            try:
+                import sha
+                self.hash = sha.new()
+                self.hash_len = 20
+            except:
+                import md5
+                self.hash = md5.new()
+                self.hash_len = 16
+        self.pool = '\0' * self.hash_len
+        self.stir(seed)
+
+    def stir(self, entropy):
+        bytes = [ord(c) for c in self.pool]
+        for c in entropy:
+            if self.pool_index == self.hash_len:
+                self.pool_index = 0
+            b = ord(c) & 0xff
+            bytes[self.pool_index] ^= b
+            self.pool_index += 1
+        self.pool = ''.join([chr(c) for c in bytes])
+
+    def random_8(self):
+        if self.digest is None or self.next_byte == self.hash_len:
+            self.hash.update(self.pool)
+            self.digest = self.hash.digest()
+            self.stir(self.digest)
+            self.next_byte = 0
+        value = ord(self.digest[self.next_byte])
+        self.next_byte += 1
+        return value
+
+    def random_16(self):
+        return self.random_8() * 256 + self.random_8()
+
+    def random_32(self):
+        return self.random_16() * 65536 + self.random_16()
+
+    def random_between(self, first, last):
+        size = last - first + 1
+        if size > 4294967296L:
+            raise ValueError, 'too big'
+        if size > 65536:
+            rand = self.random_32
+            max = 4294967295L
+        elif size > 256:
+            rand = self.random_16
+            max = 65535
+        else:
+            rand = self.random_8
+            max = 255
+	return (first + size * rand() // (max + 1))
+
+pool = EntropyPool()
+
+def random_16():
+    return pool.random_16()
+
+def between(first, last):
+    return pool.random_between(first, last)