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'''Functions that load and write PEM-encoded files.'''
import base64
def load_pem(contents, pem_start, pem_end):
'''Loads a PEM file.
Only considers the information between lines "pem_start" and "pem_end". For
private keys these are '-----BEGIN RSA PRIVATE KEY-----' and
'-----END RSA PRIVATE KEY-----'
@param contents: the contents of the file to interpret
@param pem_start: the start marker of the PEM content, such as
'-----BEGIN RSA PRIVATE KEY-----'
@param pem_end: the end marker of the PEM content, such as
'-----END RSA PRIVATE KEY-----'
@return the base64-decoded content between the start and end markers.
@raise ValueError: when the content is invalid, for example when the start
marker cannot be found.
'''
pem_lines = []
in_pem_part = False
for line in contents.split('\n'):
line = line.strip()
# Handle start marker
if line == pem_start:
if in_pem_part:
raise ValueError('Seen start marker "%s" twice' % pem_start)
in_pem_part = True
continue
# Skip stuff before first marker
if not in_pem_part:
continue
# Handle end marker
if in_pem_part and line == pem_end:
in_pem_part = False
break
pem_lines.append(line)
# Do some sanity checks
if not pem_lines:
raise ValueError('No PEM start marker "%s" found' % pem_start)
if in_pem_part:
raise ValueError('No PEM end marker "%s" found' % pem_end)
# Base64-decode the contents
pem = ''.join(pem_lines)
return base64.decodestring(pem)
def save_pem(contents, pem_start, pem_end):
'''Saves a PEM file.
The PEM file will start with the 'pem_start' marker, then the
base64-encoded content, and end with the 'pem_end' marker.
@param contents: the contents to encode in PEM format
@param pem_start: the start marker of the PEM content, such as
'-----BEGIN RSA PRIVATE KEY-----'
@param pem_end: the end marker of the PEM content, such as
'-----END RSA PRIVATE KEY-----'
@return the base64-encoded content between the start and end markers.
'''
b64 = base64.encodestring(contents).strip()
pem_lines = [pem_start]
for block_start in range(0, len(b64), 64):
block = b64[block_start:block_start + 64]
pem_lines.append(block)
pem_lines.append(pem_end)
pem_lines.append('')
return '\n'.join(pem_lines)
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