HMAC algorithm as described by RFC 2104, by Gerhard Häring (SF patch

#460112).

1 files changed, 110 insertions, 0 deletions

diff --git a/Lib/hmac.py b/Lib/hmac.py
new file mode 100644
index 0000000..1315903
--- /dev/null
+++ b/Lib/hmac.py
@@ -0,0 +1,110 @@
+"""HMAC (Keyed-Hashing for Message Authentication) Python module.
+
+Implements the HMAC algorithm as described by RFC 2104.
+"""
+
+import string
+
+def _strxor(s1, s2):
+    """Utility method. XOR the two strings s1 and s2 (must have same length).
+    """
+    return "".join(map(lambda x, y: chr(ord(x) ^ ord(y)), s1, s2))
+        
+class HMAC:
+    """RFC2104 HMAC class.
+
+    This (mostly) supports the API for Cryptographic Hash Functions (PEP 247).
+    """ 
+
+    def __init__(self, key, msg = None, digestmod = None):
+        """Create a new HMAC object.
+
+        key:       key for the keyed hash object.
+        msg:       Initial input for the hash, if provided.
+        digestmod: A module supporting PEP 247. Defaults to the md5 module.
+        """
+        if digestmod == None:
+            import md5
+            digestmod = md5
+
+        self.outer = digestmod.new()
+        self.inner = digestmod.new()
+
+        blocksize = 64
+        ipad = "\x36" * blocksize
+        opad = "\x5C" * blocksize
+
+        if len(key) > blocksize:
+            key = digestmod.new(key).digest()
+
+        key = key + chr(0) * (blocksize - len(key))
+        self.outer.update(_strxor(key, opad))
+        self.inner.update(_strxor(key, ipad))
+        if (msg):
+            self.update(msg)
+
+##    def clear(self):
+##        raise NotImplementedError, "clear() method not available in HMAC."
+
+    def update(self, msg):
+        """Update this hashing object with the string msg.
+        """
+        self.inner.update(msg)
+
+    def copy(self):
+        """Return a separate copy of this hashing object.
+
+        An update to this copy won't affect the original object.
+        """
+        return HMAC(self)
+
+    def digest(self):
+        """Return the hash value of this hashing object.
+
+        This returns a string containing 8-bit data.  The object is
+        not altered in any way by this function; you can continue
+        updating the object after calling this function.
+        """
+        h = self.outer.copy()
+        h.update(self.inner.digest())
+        return h.digest()
+
+    def hexdigest(self):
+        """Like digest(), but returns a string of hexadecimal digits instead.
+        """
+        return "".join([string.zfill(hex(ord(x))[2:], 2)
+                        for x in tuple(self.digest())])
+
+def new(key, msg = None, digestmod = None):
+    """Create a new hashing object and return it.
+
+    key: The starting key for the hash.
+    msg: if available, will immediately be hashed into the object's starting
+    state.  
+
+    You can now feed arbitrary strings into the object using its update()
+    method, and can ask for the hash value at any time by calling its digest()
+    method.
+    """
+    return HMAC(key, msg, digestmod)
+
+def test():
+    def md5test(key, data, digest):
+        h = HMAC(key, data)
+        assert(h.hexdigest().upper() == digest.upper())
+
+    # Test vectors from the RFC
+    md5test(chr(0x0b) * 16,
+            "Hi There",
+            "9294727A3638BB1C13F48EF8158BFC9D")
+
+    md5test("Jefe",
+            "what do ya want for nothing?",
+            "750c783e6ab0b503eaa86e310a5db738")
+
+    md5test(chr(0xAA)*16,
+            chr(0xDD)*50,
+            "56be34521d144c88dbb8c733f0e8b3f6")
+
+if __name__ == "__main__":
+    test()