redundant, coro.asn1.ber implements BER codec

coro/ssh/keys/ber.py

-# Copyright (c) 2002-2012 IronPort Systems and Cisco Systems
-#
-# Permission is hereby granted, free of charge, to any person obtaining a copy
-# of this software and associated documentation files (the "Software"), to deal
-# in the Software without restriction, including without limitation the rights
-# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-# copies of the Software, and to permit persons to whom the Software is
-# furnished to do so, subject to the following conditions:
-#
-# The above copyright notice and this permission notice shall be included in
-# all copies or substantial portions of the Software.
-#
-# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-# SOFTWARE.
-
-#
-# ssh.keys.ber
-#
-# Very simple ASN.1 BER decoder used for SSH private keys.
-# This implements more than is necessary for SSH, but not the entire
-# ASN.1 standard.
-#
-
-import sys
-sys.stderr.write ('FIX ber.py to use coro.asn1.ber\n')
-
-__version__ = '$Revision: #1 $'
-
-# flags for BER tags
-FLAGS_UNIVERSAL       = 0x00
-FLAGS_STRUCTURED      = 0x20
-FLAGS_APPLICATION     = 0x40
-FLAGS_CONTEXT         = 0x80
-FLAGS_PRIVATE         = 0xC0
-
-# universal BER tags
-TAGS_INTEGER                   = 0x02
-TAGS_OCTET_STRING              = 0x04
-TAGS_SEQUENCE                  = 0x10 | FLAGS_STRUCTURED
-
-class DecodeError (Exception):
-    pass
-
-class InsufficientData (DecodeError):
-    pass
-
-class InvalidData (DecodeError):
-    pass
-
-class UnknownTag (DecodeError):
-    pass
-
-# SAFETY NOTE: it's important for each decoder to correctly handle length == zero.
-
-def decode_string(s, pos, length):
-    # caller guarantees sufficient data in <s>
-    result = s[pos:pos+length]
-    pos += length
-    return result, pos
-
-def decode_integer(s, pos, length):
-    if length == 0:
-        return 0, pos
-    else:
-        n = long(ord(s[pos]))
-        if n & 0x80:
-            # negative
-            n = n - 0x100
-        length -= 1
-        while length:
-            pos += 1
-            n = (n << 8) | ord(s[pos])
-            length -= 1
-        # advance past the last byte
-        pos += 1
-        return n, pos
-
-def decode_structured(s, pos, length):
-    start = pos
-    end = start + length
-    result = []
-    if length:
-        while pos < end:
-            item, pos = decode (s, pos, end)
-            result.append(item)
-    return result, pos
-
-# can an asn1 string *end* with a length?  i.e., can we just do the
-# length check once, at the front, and assume at least three bytes?
-
-def decode(s, pos=0, eos=-1):
-    """decode(s, pos=0, eos=-1) -> (value, pos)
-    Decodes a BER-encoded string.
-    Return value includes the position where decoding stopped.
-    <pos> start of scanning position.
-    <eos> end of scanning.
-    """
-    if eos == -1:
-        eos = len(s)
-    # 1) get tag
-    tag = ord(s[pos])
-    pos += 1
-    # 2) get length
-    if pos > eos:
-        # assure at least one byte [valid for length == 0]
-        raise InsufficientData, pos
-
-    a = ord(s[pos])
-    if a < 0x80:
-        # one-byte length
-        length = a
-        pos += 1
-    elif pos + 1 >= eos:
-        # assure at least two bytes
-        raise InsufficientData, pos
-    elif a == 0x81:
-        # one-byte length (0x80 <= x <= 0xff)
-        length = ord(s[pos+1])
-        pos += 2
-    elif pos + 2 >= eos:
-        # assure at least three bytes
-        raise InsufficientData, pos
-    elif a == 0x82:
-        # two-byte length (0x80 <= x <= 0xffff)
-        length = ord(s[pos+1])
-        length = (length << 8) | ord(s[pos+2])
-        pos += 3
-    else:
-        # longer lengths allowed? >0x82?
-        raise InvalidData, pos
-    # 3) get value
-    # assure at least <length> bytes
-    if (pos + length) > eos:
-        raise InsufficientData, pos
-    elif tag == TAGS_OCTET_STRING:
-        return decode_string (s, pos, length)
-    elif tag == TAGS_INTEGER:
-        return decode_integer (s, pos, length)
-    elif tag == TAGS_SEQUENCE:
-        return decode_structured (s, pos, length)
-    else:
-        raise UnknownTag, tag