Include module for desktop build

2012-09-09 17:29:09 +02:00
parent 89426d75ab
commit 36f653f65b
88 changed files with 9967 additions and 1 deletions
@@ -0,0 +1,81 @@
+#  Copyright (c) 2002-2012 Zooko Wilcox-O'Hearn
+#  This file is part of pyutil; see README.rst for licensing terms.
+
+import warnings
+
+"""
+Cryptographically strong pseudo-random number generator based on SHA256.
+"""
+
+class SHA256Expander:
+    """
+    Provide a cryptographically strong pseudo-random number generator based on
+    SHA256.  Hopefully this means that no attacker will be able to predict any
+    bit of output that he hasn't seen, given that he doesn't know anything about
+    the seed and given that he can see as many bits of output as he desires
+    except for the bit that he is trying to predict.  Further it is hoped that
+    an attacker will not even be able to determine whether a given stream of
+    random bytes was generated by this PRNG or by flipping a coin repeatedly.
+    The safety of this technique has not been verified by a Real Cryptographer.
+    ... but it is similar to the PRNG in FIPS-186...
+
+    The seed and counter are encoded in DJB's netstring format so that I
+    don't have to think about the possibility of ambiguity.
+    
+    Note: I've since learned more about the theory of secure hash functions
+    and the above is a strong assumption about a secure hash function.  Use
+    of this class should be considered deprecated and you should use a more
+    well-analyzed KDF (such as the nascent standard HKDF) or stream cipher or
+    whatever it is that you need.
+    """
+    def __init__(self, seed=None):
+        warnings.warn("deprecated", DeprecationWarning)
+        if seed is not None:
+            self.seed(seed)
+
+    def seed(self, seed):
+        import hashlib
+        self.starth = hashlib.sha256('24:pyutil hash expansion v2,10:algorithm:,6:SHA256,6:value:,')
+        seedlen = len(seed)
+        seedlenstr = str(seedlen)
+        self.starth.update(seedlenstr)
+        self.starth.update(':')
+        self.starth.update(seed)
+        self.starth.update(',')
+
+        self.avail = ""
+        self.counter = 0
+
+    def get(self, bytes):
+        bytesleft = bytes
+
+        res = []
+
+        while bytesleft > 0:
+            if len(self.avail) == 0:
+                h = self.starth.copy()
+                counterstr = str(self.counter)
+                counterstrlen = len(counterstr)
+                counterstrlenstr = str(counterstrlen)
+                h.update(counterstrlenstr)
+                h.update(':')
+                h.update(counterstr)
+                h.update(',')
+                self.avail = h.digest()
+                self.counter += 1
+
+            numb = min(len(self.avail), bytesleft)
+
+            (chunk, self.avail,) = (self.avail[:numb], self.avail[numb:],)
+
+            res.append(chunk)
+            
+            bytesleft = bytesleft - numb
+
+        resstr = ''.join(res)
+        assert len(resstr) == bytes
+
+        return resstr
+
+def sha256expand(inpstr, expbytes):
+    return SHA256Expander(inpstr).get(expbytes)