rsa_source/rsa/pem.py

   1 # -*- coding: utf-8 -*-
   2 #
   3 #  Copyright 2011 Sybren A. Stüvel <sybren@stuvel.eu>
   4 #
   5 #  Licensed under the Apache License, Version 2.0 (the "License");
   6 #  you may not use this file except in compliance with the License.
   7 #  You may obtain a copy of the License at
   8 #
   9 #      http://www.apache.org/licenses/LICENSE-2.0
  10 #
  11 #  Unless required by applicable law or agreed to in writing, software
  12 #  distributed under the License is distributed on an "AS IS" BASIS,
  13 #  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14 #  See the License for the specific language governing permissions and
  15 #  limitations under the License.
  16
  17 '''Functions that load and write PEM-encoded files.'''
  18
  19 import base64
  20
  21 def _markers(pem_marker):
  22     '''Returns the start and end PEM markers
  23
  24     >>> _markers('RSA PRIVATE KEY')
  25     ('-----BEGIN RSA PRIVATE KEY-----', '-----END RSA PRIVATE KEY-----')
  26
  27     '''
  28
  29     return ('-----BEGIN %s-----' % pem_marker,
  30             '-----END %s-----' % pem_marker)
  31
  32 def load_pem(contents, pem_marker):
  33     '''Loads a PEM file.
  34
  35     @param contents: the contents of the file to interpret
  36     @param pem_marker: the marker of the PEM content, such as 'RSA PRIVATE KEY'
  37         when your file has '-----BEGIN RSA PRIVATE KEY-----' and
  38         '-----END RSA PRIVATE KEY-----' markers.
  39
  40     @return the base64-decoded content between the start and end markers.
  41
  42     @raise ValueError: when the content is invalid, for example when the start
  43         marker cannot be found.
  44
  45     '''
  46
  47     (pem_start, pem_end) = _markers(pem_marker)
  48
  49     pem_lines = []
  50     in_pem_part = False
  51
  52     for line in contents.split('\n'):
  53         line = line.strip()
  54
  55         # Skip empty lines
  56         if not line:
  57             continue
  58
  59         # Handle start marker
  60         if line == pem_start:
  61             if in_pem_part:
  62                 raise ValueError('Seen start marker "%s" twice' % pem_start)
  63
  64             in_pem_part = True
  65             continue
  66
  67         # Skip stuff before first marker
  68         if not in_pem_part:
  69             continue
  70
  71         # Handle end marker
  72         if in_pem_part and line == pem_end:
  73             in_pem_part = False
  74             break
  75
  76         # Load fields
  77         if ':' in line:
  78             continue
  79
  80         pem_lines.append(line)
  81
  82     # Do some sanity checks
  83     if not pem_lines:
  84         raise ValueError('No PEM start marker "%s" found' % pem_start)
  85
  86     if in_pem_part:
  87         raise ValueError('No PEM end marker "%s" found' % pem_end)
  88
  89     # Base64-decode the contents
  90     pem = ''.join(pem_lines)
  91     return base64.decodestring(pem)
  92
  93 def save_pem(contents, pem_marker):
  94     '''Saves a PEM file.
  95
  96     @param contents: the contents to encode in PEM format
  97     @param pem_marker: the marker of the PEM content, such as 'RSA PRIVATE KEY'
  98         when your file has '-----BEGIN RSA PRIVATE KEY-----' and
  99         '-----END RSA PRIVATE KEY-----' markers.
 100
 101     @return the base64-encoded content between the start and end markers.
 102
 103     '''
 104
 105     (pem_start, pem_end) = _markers(pem_marker)
 106
 107     b64 = base64.encodestring(contents).replace('\n', '')
 108     pem_lines = [pem_start]
 109
 110     for block_start in range(0, len(b64), 64):
 111         block = b64[block_start:block_start + 64]
 112         pem_lines.append(block)
 113
 114     pem_lines.append(pem_end)
 115     pem_lines.append('')
 116
 117     return '\n'.join(pem_lines)
 118