GPGMail: Sending emails without MDC

Johnny's Avatar

Johnny

12 Jun, 2018 12:56 PM

Received email with MDC error (encryption aborted). Replied to all, sent email successfully signed + encrypted. Browse to Sent folder, open my reply, I only see two files “Mail attachment” and “encrypted.asc” with message “Decryption of the message was aborted”, with details “The modification detection code (MDC) for this encrypted message is missing or has been modified. This could mean that an attacker has been trying to modify the contents within the encrypted message. Please have the message re-sent to you and tell the sender, that their encrypted message didn't include a modification detection code.” Also, the recipients couldn’t open the email.

I tried sending a new email to the same recipients (instead of a forward or reply-all); same error, the recipients couldn’t open the email.

I checked my sent folder and noticed that also I couldn’t open both emails I sent (both the new email as well as the reply-all email). Seems the GPG on my side is stripping the email of MDC or modifying it?!

I checked the showpref for each recipient key (including my key), and all show MDC as a feature.

I sent an email to each person individually (including to myself), and all worked without error. So seems to be a bug when sending to multiple recipients?

Expected
That all emails sent from my client would have a MDC.

Additional info
gpg (GnuPG) 2.2.8
libgcrypt 1.8.2
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later https://gnu.org/licenses/gpl.html
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Home: /Users/jd/.gnupg
Supported algorithms:
Pubkey: RSA, ELG, DSA, ECDH, ECDSA, EDDSA
Cipher: IDEA, 3DES, CAST5, BLOWFISH, AES, AES192, AES256, TWOFISH,
CAMELLIA128, CAMELLIA192, CAMELLIA256 Hash: SHA1, RIPEMD160, SHA256, SHA384, SHA512, SHA224
Compression: Uncompressed, ZIP, ZLIB, BZIP2

Using GPG Suite 2018.2, nightly 2205n

macOS                   10.13.5     17F77
GPG Suite               2018.2      2205n   (bef9c89)
GPGMail                 3.0         1315n   (3d99a0fc)
GPG Keychain            1.4.3       1454n   (715e771)
GPGServices             1.11.3      1005n   (185b7dd)
MacGPG                  2.2.7       910n    (099ae46)
GPG Suite Preferences   2.1.2       1034n   (1a09bc7)
Libmacgpg               0.8.4       859n    (f7976ad)
pinentry                1.1.1       26n     (74d8675)
  1. Support Staff 1 Posted by Steve on 23 Jun, 2018 12:24 PM

    Steve's Avatar

    Hi Johnny,

    please excuse the late reply. Please update to GPG Suite 2018.3 if you haven't already.

    What happens if you send yourself an encrypted + signed email? Are you also seeing the no MDC error?

    Best,
    steve

  2. 2 Posted by JD on 25 Jun, 2018 05:29 AM

    JD's Avatar

    Hi Steve!

    Please excuse my late reply also. I’ve updated to the latest version. It could be that the issue is with other people’s mail clients, as I checked each recipient key individually and they all have MDC enabled under features, and when sending to each individually I can decrypt, however when sending to them all I get the error, even if it’s a new email.

    I will run some further troubleshooting as soon as I get the chance and will let you know if I find any new clues.

    Thanks,
    Johnny

  3. Support Staff 3 Posted by Steve on 25 Jun, 2018 11:36 AM

    Steve's Avatar

    So the test to send yourself an encrypted + signed email works just fine?

    My feeling tells me that there may be an issue with one of the keys. It would be important to play with the keys and see if you are somehow able to isolate when the problem occurs and what factors trigger it.

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