Implement better detection of "multipart/encrypted" email with PGP encrypted message

[martgil]

Description: The FlowCrypt iOS didn't recognize "multipart/encrypted" email with PGP encrypted message. Emails at https://mail.google.com/mail/u/[email protected]/#inbox/FMfcgzGxTFXMFnDNbgknpqvXKtSmMgSK isn't recognized by the FlowCrypt app and shows not encrypted + no signed blank email thread.

Reference:

• #5726 Improve encrypted message detection for multipart/encrypted email flowcrypt-browser#5727
• https://github.com/FlowCrypt/flowcrypt-android/blob/e58d040f8eade675ca8c6bd18cb608d46bcdb44b/FlowCrypt/src/main/java/com/flowcrypt/email/extensions/jakarta/mail/PartExt.kt#L82

[ioanmo226]

@sosnovsky I think better to finish this task first and then release current 1.3.1 version?

[sosnovsky]

Yes, after fixing this one we can publish a new release to App Store and switch back to flowcrypt-browser tasks.

[ioanmo226]

@sosnovsky I don't have task assigned for iOS at the moment as you plan to migrate to Swift6 in the future. Do I have to move on browser extension?

[sosnovsky]

Oh, I've missed that this one was assigned to Mart, re-assigned it to you

[ioanmo226]

Okay, I see
I thought Mart was already working on it.

[ioanmo226]

@martgil I can reproduce this issue in iOS app with email flowcrypt.compatibility account.
However could you guide me how to reproduce such email for UI testing?
Thank you

[martgil]

Hi @ioanmo226, I'll try if I can craft one for you. Reason is that, the particular test email we have was just sent by the user and haven't had the chance to know to generate one for ourselves that time.

[martgil]

Hello @ioanmo226 - I can't seemed to craft a test email for this one easily, may I ask for a little more time.

Upon reviewing, it possibly be able to craft such email by using Enigmail in Thunderbird but upon testing, the Enigmail extension is no longer available and supported by Thunderbird Client.

My plan is to craft and send a mime email that contains the following format in the test email from: FlowCrypt/flowcrypt-browser#5726, in which, it has "multipart/encrypted" part that has 2 attachment of the following:

1.) noname file with content: Version: 1.
2.) noname file with content:

Version: 1
----BEGIN PGP MESSAGE-----

Encrypted message goes here...
-----END PGP MESSAGE-----

[ioanmo226]

I see. Thank you
No problem
I haven't even implemented a fix yet.

[martgil]

Hello @ioanmo226, there's some bad news here. I'm unable to generate such email even after making such similar mime email.

I'm using the python (3.11.9) code below, while it sends similar mime email and being recognizable by FlowCrypt, the decryption fails:

import smtplib
from email.mime.multipart import MIMEMultipart
from email.mime.base import MIMEBase
from email import encoders

# Email account credentials
sender_email = "[email protected]"
recipient_email = "[email protected]"
password = "app specific password" # this canbe obtained in https://myaccount.google.com/apppasswords

boundary = "----=_Part_7_39145192.1715228097793"
msg = MIMEMultipart("encrypted", boundary=boundary)
msg["From"] = sender_email
msg["To"] = recipient_email
msg["Subject"] = "test multipart/encrypted"
msg["MIME-Version"] = "1.0"  

pgp_encrypted_part = MIMEBase("application", "pgp-encrypted")
pgp_encrypted_part.add_header("Content-Transfer-Encoding", "7bit")
pgp_encrypted_part.set_payload("Version: 1")

# The email.txt contains ascii armored pgp encrypted email similar to the sample email in flowcrypt.compatibility
with open("email.txt", "r") as file:
    encrypted_message = file.read()

pgp_data_part = MIMEBase("application", "octet-stream")
pgp_data_part.add_header("Content-Transfer-Encoding", "7bit")
pgp_data_part.set_payload(encrypted_message)

msg.attach(pgp_encrypted_part) 
msg.attach(pgp_data_part)       

# Send the email via Gmail's SMTP server
with smtplib.SMTP_SSL("smtp.gmail.com", 465) as server:
    server.login(sender_email, password)
    server.sendmail(sender_email, recipient_email, msg.as_string())

print("Email sent successfully.")

[ioanmo226]

You mean that test email was recognized by Flowcrypt which means Flowcrypt knows it is PGP but can't decrypt that email?

[martgil]

Yes, that's what is happening in the test email generated using the python script when opened through the FlowCrypt browser extension.

[ioanmo226]

I see.
Seems like I have to replace sensitive infos from test email from flowcrypt compatibility email.(Like you did in FlowCrypt/flowcrypt-browser#5727)

[martgil]

If I remember it correctly, what I did there was just to replace the sensitive infos like exact email subject and sender while retaining the format for a "multipart/encrypted" mime email.