1 files changed, 178 insertions, 0 deletions
diff --git a/python/PyECC/ecc/encoding.py b/python/PyECC/ecc/encoding.py
new file mode 100644
index 000000000..24d3eb5a8
--- /dev/null
+++ b/python/PyECC/ecc/encoding.py
@@ -0,0 +1,178 @@
+#
+#   Encodings and Formats for Elliptic Curve Cryptography
+#
+
+import StringIO
+
+# Big-Endian Encoding
+
+def enc_long(n):
+    '''Encodes arbitrarily large number n to a sequence of bytes.
+    Big endian byte order is used.'''
+    s = ""
+    while n > 0:
+        s = chr(n & 0xFF) + s
+        n >>= 8
+    return s
+
+def enc_int(n):
+    '''Encodes an integer n to a 4-byte string.
+    Big endian byte order is used.'''
+    return chr((n >> 24) & 0xFF) + chr((n >> 16) & 0xFF) + \
+           chr((n >>  8) & 0xFF) + chr( n        & 0xFF)
+
+def enc_fixed_long(n, length):
+    return enc_long(n)[:length].rjust(length, '\x00')
+
+def dec_long(s):
+    '''Decodes s to its numeric representation.
+    Big endian byte order is used.'''
+    n = 0
+    for c in s:
+        n = (n << 8) | ord(c)
+    return n
+
+# dec_int not necessary,
+# dec_long does the same when provided with 4 bytes input.
+
+# Chunks
+
+def enc_chunks(*args):
+    '''Chain given string args or sub-chunks to a single chunk'''
+    return ''.join([enc_int(len(a)) + a for a in args])
+
+def dec_chunks(s):
+    '''Split a chunk into strings or sub-chunks'''
+    i = 0
+    result = []
+    while i < len(s):
+        size = dec_long(s[i : i + 4])
+        i += 4
+        result.append(s[i : i + size])
+        i += size
+    return result
+
+# Point and signature data
+
+def enc_point(p):
+    '''Encode a point p = (x, y)'''
+    x, y = p
+    sx = enc_long(x)
+    sy = enc_long(y)
+    diff = len(sx) - len(sy)
+    if diff > 0:
+        sy = '\x00' * diff + sy
+    elif diff < 0:
+        sx = '\x00' * -diff + sx
+    return sx + sy
+
+def dec_point(s):
+    '''Decode an even length string s to a point(x, y)'''
+    d = len(s) / 2
+    return (dec_long(s[:d]), dec_long(s[d:]))
+
+
+class Encoder:
+
+    def __init__(self):
+        self._io = StringIO.StringIO()
+
+    def int(self, n, size = 4):
+        self._io.write(enc_fixed_long(n, size))
+        return self
+
+    def long(self, n, pre = 2):
+        lstr = enc_long(n)
+        self._io.write(enc_fixed_long(len(lstr), pre) + lstr)
+        return self
+
+    def str(self, s, pre = 2):
+        self._io.write(enc_fixed_long(len(s), pre) + s)
+        return self
+
+    def point(self, p, pre = 2):
+        lstr = enc_point(p)
+        self._io.write(enc_fixed_long(len(lstr), pre) + lstr)
+        return self
+
+    def chunk(self, enc, pre = 2):
+        lstr = enc.out()
+        self._io.write(enc_fixed_long(len(lstr), pre) + lstr)
+        return self
+
+    def out(self):
+        return self._io.getvalue()
+
+class Decoder:
+
+    def __init__(self, data, offset = 0):
+        self._io = StringIO.StringIO(data)
+        self._io.seek(offset)
+        self._res = []
+        self._limit = None
+        self._parent = None
+
+    def _ret(self):
+##        if self._parent and self._io.tell() >= self._limit:
+##            return self.exit()
+##        else:
+##            return self
+        return self
+
+    def int(self, size = 4):
+        self._res.append(dec_long(self._io.read(size)))
+        return self._ret()
+        
+
+    def long(self, pre = 2):
+        llen = dec_long(self._io.read(pre))
+        self._res.append(dec_long(self._io.read(llen)))
+        return self._ret()
+
+    def str(self, pre = 2):
+        llen = dec_long(self._io.read(pre))
+        self._res.append(self._io.read(llen))
+        return self._ret()
+
+    def point(self, pre = 2):
+        llen = dec_long(self._io.read(pre))
+        self._res.append(dec_point(self._io.read(llen)))
+        return self._ret()
+
+    def enter(self, pre = 2):
+        llen = dec_long(self._io.read(pre))
+        subcoder = Decoder("")
+        subcoder._io = self._io
+        subcoder._parent = self
+        subcoder._limit = self._io.tell() + llen
+        return subcoder
+
+    def chunk(self, pre = 2):
+        llen = dec_long(self._io.read(pre))
+        self._res.append(Decoder(self._io.read(llen)))
+        return self._ret()
+
+    def exit(self):
+        if self._parent:
+            self._parent._io.seek(self._limit)
+            self._parent._res.append(self._res)
+            return self._parent
+        else:
+            raise RuntimeError, "Cannont exit top level Decoder"
+
+    def continues(self):
+        return (not self._limit) or (self._io.tell() < self._limit)
+
+    def out(self, exit_all = False):
+        if exit_all and self._parent:
+            return self.exit().out()
+        else:
+            r = self._res
+            self._res = []
+            return r
+
+    def only(self):
+        if self._res:
+            return self._res.pop(0)
+        else:
+            return RuntimeError, "Only what? (Empty decoder stack)"