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# Copyright (C) 2011-2012 Patrick Totzke <patricktotzke@gmail.com>
# This file is released under the GNU GPL, version 3 or a later revision.
# For further details see the COPYING file
import re
from email.generator import Generator
from cStringIO import StringIO
from alot.errors import GPGProblem
from email.mime.multipart import MIMEMultipart
import gpgme
def email_as_string(mail):
"""
Converts the given message to a string, without mangling "From" lines
(like as_string() does).
:param mail: email to convert to string
:rtype: str
"""
fp = StringIO()
g = Generator(fp, mangle_from_=False, maxheaderlen=78)
g.flatten(mail)
as_string = RFC3156_canonicalize(fp.getvalue())
if isinstance(mail, MIMEMultipart):
# Get the boundary for later
boundary = mail.get_boundary()
# Workaround for http://bugs.python.org/issue14983:
# Insert a newline before the outer mail boundary so that other mail
# clients can verify the signature when sending an email which contains
# attachments.
as_string = re.sub(r'--(\r\n)--' + boundary,
'--\g<1>\g<1>--' + boundary,
as_string, flags=re.MULTILINE)
return as_string
def _hash_algo_name(hash_algo):
"""
Re-implements GPGME's hash_algo_name as long as pygpgme doesn't wrap that
function.
:param hash_algo: GPGME hash_algo
:rtype: str
"""
mapping = {
gpgme.MD_MD5: "MD5",
gpgme.MD_SHA1: "SHA1",
gpgme.MD_RMD160: "RIPEMD160",
gpgme.MD_MD2: "MD2",
gpgme.MD_TIGER: "TIGER192",
gpgme.MD_HAVAL: "HAVAL",
gpgme.MD_SHA256: "SHA256",
gpgme.MD_SHA384: "SHA384",
gpgme.MD_SHA512: "SHA512",
gpgme.MD_MD4: "MD4",
gpgme.MD_CRC32: "CRC32",
gpgme.MD_CRC32_RFC1510: "CRC32RFC1510",
gpgme.MD_CRC24_RFC2440: "CRC24RFC2440",
}
if hash_algo in mapping:
return mapping[hash_algo]
else:
raise GPGProblem(("Invalid hash_algo passed to hash_algo_name."
" Please report this as a bug in alot."))
def RFC3156_micalg_from_algo(hash_algo):
"""
Converts a GPGME hash algorithm name to one conforming to RFC3156.
GPGME returns hash algorithm names such as "SHA256", but RFC3156 says that
programs need to use names such as "pgp-sha256" instead.
:param hash_algo: GPGME hash_algo
:rtype: str
"""
# hash_algo will be something like SHA256, but we need pgp-sha256.
hash_algo = _hash_algo_name(hash_algo)
return 'pgp-' + hash_algo.lower()
def RFC3156_canonicalize(text):
"""
Canonicalizes plain text (MIME-encoded usually) according to RFC3156.
This function works as follows (in that order):
1. Convert all line endings to \\\\r\\\\n (DOS line endings).
2. Ensure the text ends with a newline (\\\\r\\\\n).
3. Encode all occurences of "From " at the beginning of a line
to "From=20" in order to prevent other mail programs to replace
this with "> From" (to avoid MBox conflicts) and thus invalidate
the signature.
:param text: text to canonicalize (already encoded as quoted-printable)
:rtype: str
"""
text = re.sub("\r?\n", "\r\n", text)
if not text.endswith("\r\n"):
text += "\r\n"
text = re.sub("^From ", "From=20", text, flags=re.MULTILINE)
return text
def get_key(keyid):
"""
Gets a key from the keyring by filtering for the specified keyid, but
only if the given keyid is specific enough (if it matches multiple
keys, an exception will be thrown).
:param keyid: filter term for the keyring (usually a key ID)
:rtype: gpgme.Key
"""
ctx = gpgme.Context()
try:
key = ctx.get_key(keyid)
except gpgme.GpgmeError as e:
if e.code == gpgme.ERR_AMBIGUOUS_NAME:
# Deferred import to avoid a circular import dependency
from alot.db.errors import GPGProblem
raise GPGProblem(("More than one key found matching this filter."
" Please be more specific (use a key ID like 4AC8EE1D)."))
else:
raise e
return key
def detached_signature_for(plaintext_str, key=None):
"""
Signs the given plaintext string and returns the detached signature.
A detached signature in GPG speak is a separate blob of data containing
a signature for the specified plaintext.
:param plaintext_str: text to sign
:param key: gpgme_key_t object representing the key to use
:rtype: tuple of gpgme.NewSignature array and str
"""
ctx = gpgme.Context()
ctx.armor = True
if key is not None:
ctx.signers = [key]
plaintext_data = StringIO(plaintext_str)
signature_data = StringIO()
sigs = ctx.sign(plaintext_data, signature_data, gpgme.SIG_MODE_DETACH)
signature_data.seek(0, 0)
signature = signature_data.read()
return sigs, signature
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