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import base64
import regex as re
import six
import time
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.asymmetric import padding
_BODY_TRAILING_WSP = re.compile(br"[\t ]+\r\n")
_BODY_WSP_RE = re.compile(br"[\t ]+")
class SimpleCanonicalization(object):
name = b"simple"
def canonicalize_header(self, header, value):
return header, value
def canonicalize_body(self, body):
return body.rstrip(b"\r\n") + b"\r\n"
class RelaxedCanonicalization(object):
name = b"relaxed"
def canonicalize_header(self, header, value):
header = header.lower()
value = _BODY_WSP_RE.sub(b" ", value.replace(b"\r\n", b""))
return header, value.strip() + b"\r\n"
def canonicalize_body(self, body):
body = _BODY_TRAILING_WSP.sub(b"\r\n", body)
body = _BODY_WSP_RE.sub(b" ", body)
body = body.rstrip(b"\r\n")
return body + b"\r\n" if body else b""
class NoFWSCanonicalization(object):
_header_fws_re = re.compile(br"[\t \r\n]+")
_body_orphan_cr_re = re.compile(br"\r([^\n])")
def canonicalize_header(self, header, value):
return header, self._header_fws_re.sub(b"", value) + b"\r\n"
def canonicalize_body(self, body):
body = _BODY_WSP_RE.sub(b"", body)
body = self._body_orphan_cr_re.sub(br"\1", body)
body = body.rstrip()
return body + b"\r\n" if body else b""
def _fold(header):
"""Fold a header line into multiple crlf-separated lines at column 72."""
i = header.rfind(b"\r\n ")
if i == -1:
pre = b""
else:
i += 3
pre = header[:i]
header = header[i:]
while len(header) > 72:
i = header[:72].rfind(b" ")
if i == -1:
i = j = 72
else:
j = i + 1
pre += header[:i] + b"\r\n "
header = header[j:]
return pre + header
class DomainKeySigner(object):
def __init__(self, key, selector, domain, signed_headers=None):
self._key = key
self._selector = selector
if six.PY3 and isinstance(selector, six.text_type):
self._selector = selector.encode('utf-8')
self._domain = domain
if six.PY3 and isinstance(domain, six.text_type):
self._domain = domain.encode('utf-8')
self._signed_headers = None
def sign(self, message):
canonicalization = NoFWSCanonicalization()
signer = self._key.signer(padding.PKCS1v15(), hashes.SHA1())
if six.PY3 and isinstance(message, six.text_type):
message = message.encode('utf-8')
headers, body = _rfc822_parse(message)
h_field = []
for header, value in headers:
if self._signed_headers is None or header in self._signed_headers:
h_field.append(header)
header, value = canonicalization.canonicalize_header(
header, value)
signer.update(header)
signer.update(b":")
signer.update(value)
body = canonicalization.canonicalize_body(body)
if body:
signer.update(b"\r\n")
signer.update(body)
return _fold(b"DomainKey-Signature: a=rsa-sha1; c=nofws; d=%s; s=%s;"
b" q=dns; h=%s; b=%s"
% (self._domain,
self._selector,
b": ".join(h_field),
base64.b64encode(signer.finalize()))) + b"\r\n"
class DKIMSigner(object):
def __init__(self, key, selector, domain,
header_canonicalization=SimpleCanonicalization(),
body_canonicalization=SimpleCanonicalization(),
signed_headers=None):
self._key = key
self._selector = selector
if six.PY3 and isinstance(selector, six.text_type):
self._selector = selector.encode('utf-8')
self._domain = domain
if six.PY3 and isinstance(domain, six.text_type):
self._domain = domain.encode('utf-8')
self._header_canonicalization = header_canonicalization
self._body_canonicalization = body_canonicalization
self._signed_headers = signed_headers
def sign(self, message, current_time=None):
if current_time is None:
current_time = int(time.time())
signer = self._key.signer(padding.PKCS1v15(), hashes.SHA256())
headers, body = _rfc822_parse(message)
h_field = []
for header, value in headers:
if self._signed_headers is None or header in self._signed_headers:
h_field.append(header)
h, v = self._header_canonicalization.canonicalize_header(
header, value)
signer.update(h)
signer.update(b":")
signer.update(v)
h = hashes.Hash(hashes.SHA256(), backend=default_backend())
h.update(self._body_canonicalization.canonicalize_body(body))
dkim_header_value = _fold(b" a=rsa-sha256; v=1; c=%s/%s; d=%s; "
b"q=dns/txt; s=%s; t=%d; h=%s; bh=%s; b="
% (self._header_canonicalization.name,
self._body_canonicalization.name,
self._domain,
self._selector,
current_time,
b": ".join(h_field),
base64.b64encode(h.finalize())))
h, v = self._header_canonicalization.canonicalize_header(
b"DKIM-Signature", dkim_header_value)
signer.update(h)
signer.update(b":")
signer.update(v)
return b"DKIM-Signature:%s%s\r\n" % (
v, _fold(base64.b64encode(signer.finalize())))
_RFC822_NEWLINE_RE = re.compile(br"\r?\n")
_RFC822_WS_RE = re.compile(br"[\t ]")
_RFC822_HEADER_RE = re.compile(br"([\x21-\x7e]+?):")
def _rfc822_parse(message):
headers = []
lines = _RFC822_NEWLINE_RE.split(message)
i = 0
while i < len(lines):
if len(lines[i]) == 0:
# End of headers, return what we have plus the body, excluding the
# blank line.
i += 1
break
if _RFC822_WS_RE.match(lines[i][:1]):
headers[-1][1] += lines[i] + b"\r\n"
else:
m = _RFC822_HEADER_RE.match(lines[i])
if m is not None:
headers.append([m.group(1), lines[i][m.end(0):] + b"\r\n"])
elif lines[i].startswith(b"From "):
pass
else:
raise ValueError("Unexpected characters in RFC822 header: %s"
% lines[i])
i += 1
return (headers, b"\r\n".join(lines[i:]))
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