1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
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)"
|
