a signature key should be set as a fallback key

[edward.git] / edward

#! /usr/bin/env python3
# -*- coding: utf-8 -*-
"""*********************************************************************
* Edward is free software: you can redistribute it and/or modify       *
* it under the terms of the GNU Affero Public License as published by  *
* the Free Software Foundation, either version 3 of the License, or    *
* (at your option) any later version.                                  *
*                                                                      *
* Edward is distributed in the hope that it will be useful,            *
* but WITHOUT ANY WARRANTY; without even the implied warranty of       *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the        *
* GNU Affero Public License for more details.                          *
*                                                                      *
* You should have received a copy of the GNU Affero Public License     *
* along with Edward.  If not, see <http://www.gnu.org/licenses/>.      *
*                                                                      *
* Copyright (C) 2014-2015 Andrew Engelbrecht                (AGPLv3+)  *
* Copyright (C) 2014      Josh Drake                        (AGPLv3+)  *
* Copyright (C) 2014      Lisa Marie Maginnis               (AGPLv3+)  *
* Copyright (C) 2009-2015 Tails developers <tails@boum.org> ( GPLv3+)  *
* Copyright (C) 2009      W. Trevor King <wking@drexel.edu> ( GPLv2+)  *
*                                                                      *
* Special thanks to Josh Drake for writing the original edward bot! :) *
*                                                                      *
************************************************************************

Code sourced from these projects:

  * http://agpl.fsf.org/emailselfdefense.fsf.org/edward/CURRENT/edward.tar.gz
  * https://git-tails.immerda.ch/whisperback/tree/whisperBack/encryption.py?h=feature/python3
  * http://www.physics.drexel.edu/~wking/code/python/send_pgp_mime
"""

import sys
import gpgme
import re
import io
import os
import importlib

import email.parser
import email.message
import email.encoders

from email.mime.multipart       import MIMEMultipart
from email.mime.application     import MIMEApplication
from email.mime.nonmultipart    import MIMENonMultipart

import edward_config

langs = ["an", "de", "el", "en", "fr", "ja", "pt-br", "ro", "ru", "tr"]

match_types =  [('clearsign',
                '-----BEGIN PGP SIGNED MESSAGE-----.*?-----BEGIN PGP SIGNATURE-----.*?-----END PGP SIGNATURE-----'),
                ('message',
                '-----BEGIN PGP MESSAGE-----.*?-----END PGP MESSAGE-----'),
                ('pubkey',
                '-----BEGIN PGP PUBLIC KEY BLOCK-----.*?-----END PGP PUBLIC KEY BLOCK-----'),
                ('detachedsig',
                '-----BEGIN PGP SIGNATURE-----.*?-----END PGP SIGNATURE-----')]


class EddyMsg (object):
    def __init__(self):
        self.multipart          = False
        self.subparts           = []

        self.charset            = None
        self.payload_bytes      = None
        self.payload_pieces     = []

        self.filename           = None
        self.content_type       = None
        self.description_list   = None


class PayloadPiece (object):
    def __init__(self):
        self.piece_type         = None
        self.string             = None
        self.gpg_data           = None


class GPGData (object):
    def __init__(self):
        self.decrypted          = False

        self.plainobj           = None
        self.sigs               = []
        self.keys               = []

class ReplyInfo (object):
    def __init__(self):
        self.replies                = None

        self.target_key             = None
        self.fallback_target_key    = None
        self.msg_to_quote           = ""

        self.success_decrypt        = False
        self.failed_decrypt         = False
        self.public_key_received    = False
        self.no_public_key          = False
        self.sig_success            = False
        self.sig_failure            = False


def main ():

    handle_args()

    gpgme_ctx = get_gpg_context(edward_config.gnupghome,
                              edward_config.sign_with_key)

    email_text = sys.stdin.read()
    email_struct = parse_pgp_mime(email_text, gpgme_ctx)

    email_to, email_from, email_subject = email_to_from_subject(email_text)
    lang = import_lang(email_to)

    replyinfo_obj = ReplyInfo()
    replyinfo_obj.replies = lang.replies

    prepare_for_reply(email_struct, replyinfo_obj)
    encrypt_to_key = get_key_from_fp(replyinfo_obj, gpgme_ctx)
    reply_plaintext = write_reply(replyinfo_obj)

    # TODO error handling for missing keys and setting .no_public_key
    reply_mime = generate_encrypted_mime(reply_plaintext, email_from, \
                                         email_subject, encrypt_to_key,
                                         gpgme_ctx)

    print(reply_mime)


def get_gpg_context (gnupghome, sign_with_key_fp):

    os.environ['GNUPGHOME'] = gnupghome

    gpgme_ctx = gpgme.Context()
    gpgme_ctx.armor = True

    try:
        sign_with_key = gpgme_ctx.get_key(sign_with_key_fp)
    except:
        error("unable to load signing key. is the gnupghome "
                + "and signing key properly set in the edward_config.py?")
        exit(1)

    gpgme_ctx.signers = [sign_with_key]

    return gpgme_ctx


def parse_pgp_mime (email_text, gpgme_ctx):

    email_struct = email.parser.Parser().parsestr(email_text)

    eddymsg_obj = parse_mime(email_struct)
    split_payloads(eddymsg_obj)
    gpg_on_payloads(eddymsg_obj, gpgme_ctx)

    return eddymsg_obj


def parse_mime(msg_struct):

    eddymsg_obj = EddyMsg()

    if msg_struct.is_multipart() == True:
        payloads = msg_struct.get_payload()

        eddymsg_obj.multipart = True
        eddymsg_obj.subparts = list(map(parse_mime, payloads))

    else:
        eddymsg_obj = get_subpart_data(msg_struct)

    return eddymsg_obj


def scan_and_split (payload_piece, match_type, pattern):

    # don't try to re-split pieces containing gpg data
    if payload_piece.piece_type != "text":
        return [payload_piece]

    flags = re.DOTALL | re.MULTILINE
    matches = re.search("(?P<beginning>.*?)(?P<match>" + pattern +
                        ")(?P<rest>.*)", payload_piece.string, flags=flags)

    if matches == None:
        pieces = [payload_piece]

    else:

        beginning               = PayloadPiece()
        beginning.string        = matches.group('beginning')
        beginning.piece_type    = payload_piece.piece_type

        match                   = PayloadPiece()
        match.string            = matches.group('match')
        match.piece_type        = match_type

        rest                    = PayloadPiece()
        rest.string             = matches.group('rest')
        rest.piece_type         = payload_piece.piece_type

        more_pieces = scan_and_split(rest, match_type, pattern)
        pieces = [beginning, match ] + more_pieces

    return pieces


def get_subpart_data (part):

    obj = EddyMsg()

    obj.charset             = part.get_content_charset()
    obj.payload_bytes       = part.get_payload(decode=True)

    obj.filename            = part.get_filename()
    obj.content_type        = part.get_content_type()
    obj.description_list    = part['content-description']

    # your guess is as good as a-myy-ee-ine...
    if obj.charset == None:
        obj.charset = 'utf-8'

    if obj.payload_bytes != None:
        try:
            payload = PayloadPiece()
            payload.string = obj.payload_bytes.decode(obj.charset)
            payload.piece_type = 'text'

            obj.payload_pieces = [payload]
        except UnicodeDecodeError:
            pass

    return obj


def do_to_eddys_pieces (function_to_do, eddymsg_obj, data):

    if eddymsg_obj.multipart == True:
        for sub in eddymsg_obj.subparts:
            do_to_eddys_pieces(function_to_do, sub, data)
    else:
        function_to_do(eddymsg_obj, data)


def split_payloads (eddymsg_obj):

    for match_type in match_types:
        do_to_eddys_pieces(split_payload_pieces, eddymsg_obj, match_type)


def split_payload_pieces (eddymsg_obj, match_type):

    (match_name, pattern) = match_type

    new_pieces_list = []
    for piece in eddymsg_obj.payload_pieces:
        new_pieces_list += scan_and_split(piece, match_name, pattern)

    eddymsg_obj.payload_pieces = new_pieces_list


def gpg_on_payloads (eddymsg_obj, gpgme_ctx, prev_parts=[]):

    if eddymsg_obj.multipart == True:
        prev_parts=[]
        for sub in eddymsg_obj.subparts:
            gpg_on_payloads (sub, gpgme_ctx, prev_parts)
            prev_parts += [sub]

        return

    for piece in eddymsg_obj.payload_pieces:

        if piece.piece_type == "text":
            # don't transform the plaintext.
            pass

        elif piece.piece_type == "message":
            (plaintext, sigs) = decrypt_block(piece.string, gpgme_ctx)

            if plaintext:
                piece.gpg_data = GPGData()
                piece.gpg_data.decrypted = True
                piece.gpg_data.sigs = sigs
                # recurse!
                piece.gpg_data.plainobj = parse_pgp_mime(plaintext, gpgme_ctx)

        elif piece.piece_type == "pubkey":
            key_fps = add_gpg_key(piece.string, gpgme_ctx)

            if key_fps != []:
                piece.gpg_data = GPGData()
                piece.gpg_data.keys = key_fps

        elif piece.piece_type == "clearsign":
            (plaintext, sig_fps) = verify_clear_signature(piece.string, gpgme_ctx)

            if sig_fps != []:
                piece.gpg_data = GPGData()
                piece.gpg_data.sigs = sig_fps
                piece.gpg_data.plainobj = parse_pgp_mime(plaintext, gpgme_ctx)

        elif piece.piece_type == "detachedsig":
            for prev in prev_parts:
                payload_bytes = prev.payload_bytes
                sig_fps = verify_detached_signature(piece.string, payload_bytes, gpgme_ctx)

                if sig_fps != []:
                    piece.gpg_data = GPGData()
                    piece.gpg_data.sigs = sig_fps
                    piece.gpg_data.plainobj = prev
                    break

        else:
            pass


def prepare_for_reply (eddymsg_obj, replyinfo_obj):

    do_to_eddys_pieces(prepare_for_reply_pieces, eddymsg_obj, replyinfo_obj)

def prepare_for_reply_pieces (eddymsg_obj, replyinfo_obj):

    for piece in eddymsg_obj.payload_pieces:
        if piece.piece_type == "text":
            # don't quote the plaintext part.
            pass

        elif piece.piece_type == "message":
            if piece.gpg_data == None:
                replyinfo_obj.failed_decrypt = True
            else:
                replyinfo_obj.success_decrypt = True

                if replyinfo_obj.target_key != None:
                    continue
                if piece.gpg_data.sigs != []:
                    replyinfo_obj.target_key = piece.gpg_data.sigs[0]
                    replyinfo_obj.msg_to_quote = flatten_payloads(piece.gpg_data.plainobj)

                # to catch public keys in encrypted blocks
                prepare_for_reply(piece.gpg_data.plainobj, replyinfo_obj)

        elif piece.piece_type == "pubkey":
            if piece.gpg_data == None:
                replyinfo_obj.no_public_key = True
            else:
                replyinfo_obj.public_key_received = True

        elif (piece.piece_type == "clearsign") \
                or (piece.piece_type == "detachedsig"):
            if piece.gpg_data == None:
                replyinfo_obj.sig_failure = True
            else:
                replyinfo_obj.sig_success = True

                if replyinfo_obj.fallback_target_key == None:
                    replyinfo_obj.fallback_target_key = piece.gpg_data.sigs[0]



def flatten_payloads (eddymsg_obj):

    flat_string = ""

    if eddymsg_obj == None:
        return ""

    if eddymsg_obj.multipart == True:
        for sub in eddymsg_obj.subparts:
            flat_string += flatten_payloads (sub)

        return flat_string

    # todo: don't include nested decrypted messages.
    for piece in eddymsg_obj.payload_pieces:
        if piece.piece_type == "text":
            flat_string += piece.string
        elif piece.piece_type == "message":
            flat_string += flatten_payloads(piece.plainobj)
        elif ((piece.piece_type == "clearsign") \
                or (piece.piece_type == "detachedsig")) \
                and (piece.gpg_data != None):
                    flat_string += flatten_payloads (piece.gpg_data.plainobj)


    return flat_string


def get_key_from_fp (replyinfo_obj, gpgme_ctx):

    if replyinfo_obj.target_key == None:
        replyinfo_obj.target_key = replyinfo_obj.fallback_target_key

    if replyinfo_obj.target_key != None:
        try:
            encrypt_to_key = gpgme_ctx.get_key(replyinfo_obj.target_key)
            return encrypt_to_key

        except:
            pass

    # no available key to use
    replyinfo_obj.target_key = None
    replyinfo_obj.fallback_target_key = None

    replyinfo_obj.no_public_key = True
    replyinfo_obj.public_key_received = False

    return None


def write_reply (replyinfo_obj):

    reply_plain = ""

    if replyinfo_obj.success_decrypt == True:
        reply_plain += replyinfo_obj.replies['success_decrypt']

        if replyinfo_obj.no_public_key == False:
            quoted_text = email_quote_text(replyinfo_obj.msg_to_quote)
            reply_plain += quoted_text

    elif replyinfo_obj.failed_decrypt == True:
        reply_plain += replyinfo_obj.replies['failed_decrypt']


    if replyinfo_obj.sig_success == True:
        reply_plain += "\n\n"
        reply_plain += replyinfo_obj.replies['sig_success']

    elif replyinfo_obj.sig_failure == True:
        reply_plain += "\n\n"
        reply_plain += replyinfo_obj.replies['sig_failure']


    if replyinfo_obj.public_key_received == True:
        reply_plain += "\n\n"
        reply_plain += replyinfo_obj.replies['public_key_received']

    elif replyinfo_obj.no_public_key == True:
        reply_plain += "\n\n"
        reply_plain += replyinfo_obj.replies['no_public_key']


    reply_plain += "\n\n"
    reply_plain += replyinfo_obj.replies['signature']

    return reply_plain


def add_gpg_key (key_block, gpgme_ctx):

    fp = io.BytesIO(key_block.encode('ascii'))

    result = gpgme_ctx.import_(fp)
    imports = result.imports

    key_fingerprints = []

    if imports != []:
        for import_ in imports:
            fingerprint = import_[0]
            key_fingerprints += [fingerprint]

            debug("added gpg key: " + fingerprint)

    return key_fingerprints


def verify_clear_signature (sig_block, gpgme_ctx):

    # FIXME: this might require the un-decoded bytes
    # or the correct re-encoding with the carset of the mime part.
    msg_fp = io.BytesIO(sig_block.encode('utf-8'))
    ptxt_fp = io.BytesIO()

    result = gpgme_ctx.verify(msg_fp, None, ptxt_fp)

    # FIXME: this might require using the charset of the mime part.
    plaintext = ptxt_fp.getvalue().decode('utf-8')

    sig_fingerprints = []
    for res_ in result:
        sig_fingerprints += [res_.fpr]

    return plaintext, sig_fingerprints


def verify_detached_signature (detached_sig, plaintext_bytes, gpgme_ctx):

    detached_sig_fp = io.BytesIO(detached_sig.encode('ascii'))
    plaintext_fp = io.BytesIO(plaintext_bytes)
    ptxt_fp = io.BytesIO()

    result = gpgme_ctx.verify(detached_sig_fp, plaintext_fp, None)

    sig_fingerprints = []
    for res_ in result:
        sig_fingerprints += [res_.fpr]

    return sig_fingerprints


def decrypt_block (msg_block, gpgme_ctx):

    block_b = io.BytesIO(msg_block.encode('ascii'))
    plain_b = io.BytesIO()

    try:
        sigs = gpgme_ctx.decrypt_verify(block_b, plain_b)
    except:
        return ("",[])

    plaintext = plain_b.getvalue().decode('utf-8')

    fingerprints = []
    for sig in sigs:
        fingerprints += [sig.fpr]
    return (plaintext, fingerprints)


def choose_reply_encryption_key (gpgme_ctx, fingerprints):

    reply_key = None
    for fp in fingerprints:
        try:
            key = gpgme_ctx.get_key(fp)

            if (key.can_encrypt == True):
                reply_key = key
                break
        except:
            continue


    return reply_key


def email_to_from_subject (email_text):

    email_struct = email.parser.Parser().parsestr(email_text)

    email_to        = email_struct['To']
    email_from      = email_struct['From']
    email_subject   = email_struct['Subject']

    return email_to, email_from, email_subject


def import_lang(email_to):

    if email_to != None:
        for lang in langs:
            if "edward-" + lang in email_to:
                lang = "lang." + re.sub('-', '_', lang)
                language = importlib.import_module(lang)

                return language

    return importlib.import_module("lang.en")


def generate_encrypted_mime (plaintext, email_from, email_subject, encrypt_to_key,
                    gpgme_ctx):

    # quoted printable encoding lets most ascii characters look normal
    # before the decrypted mime message is decoded.
    char_set = email.charset.Charset("utf-8")
    char_set.body_encoding = email.charset.QP

    # MIMEText doesn't allow setting the text encoding
    # so we use MIMENonMultipart.
    plaintext_mime = MIMENonMultipart('text', 'plain')
    plaintext_mime.set_payload(plaintext, charset=char_set)

    if (encrypt_to_key != None):

        encrypted_text = encrypt_sign_message(plaintext_mime.as_string(),
                                              encrypt_to_key,
                                              gpgme_ctx)

        control_mime = MIMEApplication("Version: 1",
                                       _subtype='pgp-encrypted',
                                       _encoder=email.encoders.encode_7or8bit)
        control_mime['Content-Description'] = 'PGP/MIME version identification'
        control_mime.set_charset('us-ascii')

        encoded_mime = MIMEApplication(encrypted_text,
                                       _subtype='octet-stream; name="encrypted.asc"',
                                       _encoder=email.encoders.encode_7or8bit)
        encoded_mime['Content-Description'] = 'OpenPGP encrypted message'
        encoded_mime['Content-Disposition'] = 'inline; filename="encrypted.asc"'
        encoded_mime.set_charset('us-ascii')

        message_mime = MIMEMultipart(_subtype="encrypted", protocol="application/pgp-encrypted")
        message_mime.attach(control_mime)
        message_mime.attach(encoded_mime)
        message_mime['Content-Disposition'] = 'inline'

    else:
        message_mime = plaintext_mime

    message_mime['To'] = email_from
    message_mime['Subject'] = email_subject

    reply = message_mime.as_string()

    return reply


def email_quote_text (text):

    quoted_message = re.sub(r'^', r'> ', text, flags=re.MULTILINE)

    return quoted_message


def encrypt_sign_message (plaintext, encrypt_to_key, gpgme_ctx):

    plaintext_bytes = io.BytesIO(plaintext.encode('ascii'))
    encrypted_bytes = io.BytesIO()

    gpgme_ctx.encrypt_sign([encrypt_to_key], gpgme.ENCRYPT_ALWAYS_TRUST,
            plaintext_bytes, encrypted_bytes)

    encrypted_txt = encrypted_bytes.getvalue().decode('ascii')
    return encrypted_txt


def error (error_msg):

    sys.stderr.write(progname + ": " + str(error_msg) + "\n")


def debug (debug_msg):

    if edward_config.debug == True:
        error(debug_msg)


def handle_args ():
    if __name__ == "__main__":

        global progname
        progname = sys.argv[0]

        if len(sys.argv) > 1:
            print(progname + ": error, this program doesn't " \
                    "need any arguments.", file=sys.stderr)
            exit(1)


main()