SSL: CERTIFICATE_VERIFY_FAILED during handshake

samaklis

I have a very simple snippet of code which makes a connection to my server running MQTT and subscribes to a topic. This is a simplified example of a bigger application. The code was working fine until today on both my iPhone and iPad.

All of the sudden I am getting an error in the Framework/pylib/ssl.py in do_handshake saying: SSL: CERTIFICATE_VERIFY_FAILED

If i take the same piece of code and run it from Windows, or Mac it works fine so to me that eliminates anything being wrong with the server.

Pythonista has not had any updates so I am at a loss as to why I am having this issue all of the sudden and especially on the Pythonista side only.

Any help would be appreciated

import paho.mqtt.client as mqtt

# The callback for when the client receives a CONNACK response from the server.
def on_connect(client, userdata, flags, rc):
    print("Connected with result code "+str(rc))

    # Subscribing in on_connect() means that if we lose the connection and
    # reconnect then subscriptions will be renewed.
    client.subscribe("weather/#")

# The callback for when a PUBLISH message is received from the server.
def on_message(client, userdata, msg):
    print(msg.topic+" "+str(msg.payload))

client = mqtt.Client(transport="websockets")
client.tls_set()
client.on_connect = on_connect
client.on_message = on_message

client.connect("myHostName", 9001, 60)

client.loop_forever()

mcriley821

If it worked fine before, it’s probably that your server has put your phone/script/whatever on a Do Not Trust list after repetitive problems.

This has some good info on identifying problems with specifically Python-based client-server setups:
https://access.redhat.com/articles/2039753

samaklis

Turns out that the service publishing to MQTT had some errors, and also Pythonista somehow was caching the handshake. After restarting both the error cleared out.

Thanks for the reply.

samaklis

Unfortunately, this issue is back again. I came to realize that there must be something related to iOS 13.5 vs 13.4.* that breaks the SSL for Pythonista. It has nothing to do with a do not trust list or configuration on the server side. Every other client can connect fine.

I noticed that the ssl.py in Pythonista is from 2016. At this point I cannot open a secure websocket connection on my iOS devices where every other client, Windows, Mac, run the below code fine. In addition browsers have no issues connecting to the server as well.

This leaves me to believe that there must be some connection to the iOS update and the SSL version in Pythonista that breaks the ability to talk via secure websocets on iOS.

I am on Pythonista version 3.3 (330025) default interpreter 3.6.1
iOS 13.5.1

I have also submitted a bug: https://github.com/omz/Pythonista-Issues/issues/652

import ssl
import socket


host = 'my_host'

context = ssl.create_default_context()

with socket.create_connection((host, 9001)) as sock:
    with context.wrap_socket(sock, server_hostname=host) as ssock:
        print(ssock.version())

I have tested the issue by installing a local version of openssl: OpenSSL 1.0.2f 28 Jan 2016 which is the same that Pythonista comes with and when I issue the command openssl s_client connect host:port I get the below (look at error in return code)

No client certificate CA names sent
Peer signing digest: SHA512
Server Temp Key: ECDH, P-256, 256 bits
---
SSL handshake has read 5357 bytes and written 443 bytes
---
New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES256-GCM-SHA384
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
    Protocol  : TLSv1.2
    Cipher    : ECDHE-RSA-AES256-GCM-SHA384
    Session-ID: 3B19973E06CB84FCBB96178FA11FE78A13AC697854FBBD51A895B39B65829C4E
    Session-ID-ctx:
    Master-Key: DDBE9EAFC7FC20E6956EB694FCF1621B495E24EAB134D5EB44BB4A22134138B638047F571DB113CCA3D86DC1C9196D8B
    Key-Arg   : None
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    TLS session ticket lifetime hint: 7200 (seconds)
    TLS session ticket:
    0000 - 04 f6 10 db 51 72 36 ff-01 ef 3a a0 16 c8 62 02   ....Qr6...:...b.
    0010 - b1 98 95 76 50 76 e4 12-af 28 d8 4c d1 26 75 2f   ...vPv...(.L.&u/
    0020 - 7a de ed e0 0b d7 0a 9f-b1 c9 6c af f3 4a 4c 1d   z.........l..JL.
    0030 - 41 7a 23 37 73 8b 21 90-2c a6 23 f7 11 30 28 8b   Az#7s.!.,.#..0(.
    0040 - 9f fc 1f d2 f9 07 f8 e5-5d a6 00 02 9d 9f ad f1   ........].......
    0050 - e1 a6 c9 48 3a 17 25 95-98 ae 16 f5 38 e0 a0 f8   ...H:.%.....8...
    0060 - ce f1 51 59 31 57 fa 30-49 39 f1 55 b9 e7 48 b7   ..QY1W.0I9.U..H.
    0070 - ae 12 a3 fb 6c 76 52 23-d5 53 08 0b 59 01 77 b2   ....lvR#.S..Y.w.
    0080 - 31 0e 3a b5 10 b7 6b a4-b6 1f 2b b5 73 af b9 c7   1.:...k...+.s...
    0090 - 7f 56 85 15 07 33 c4 4c-d9 11 00 7b 2d b1 b3 26   .V...3.L...{-..&

    Start Time: 1591927357
    Timeout   : 300 (sec)
    Verify return code: 20 (unable to get local issuer certificate)

When I run the same command with version: OpenSSL 1.1.1f 31 Mar 2020 I get no errors (look at return code=0):

No client certificate CA names sent
Peer signing digest: SHA512
Peer signature type: RSA
Server Temp Key: ECDH, P-256, 256 bits
---
SSL handshake has read 5381 bytes and written 434 bytes
Verification: OK
---
New, TLSv1.2, Cipher is ECDHE-RSA-AES256-GCM-SHA384
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
    Protocol  : TLSv1.2
    Cipher    : ECDHE-RSA-AES256-GCM-SHA384
    Session-ID: 2D876927EB37E715EACF58C6AEA2EDA5EC8EE3D4067D089C2CAE256345B83A8C
    Session-ID-ctx:
    Master-Key: 2AF552551C08BF01A0B8F166510E83BFDF03439A67698DA68502BC9B84891DD099C04545B73CD2D9EC729CF47D533AF5
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    TLS session ticket lifetime hint: 7200 (seconds)
    TLS session ticket:
    0000 - 04 f6 10 db 51 72 36 ff-01 ef 3a a0 16 c8 62 02   ....Qr6...:...b.
    0010 - 15 49 44 26 0e 71 18 58-54 27 28 0c 8b bb ce 38   .ID&.q.XT'(....8
    0020 - 5c b2 f8 33 13 f8 3a 14-ee 23 c8 c5 40 fe 80 c0   \..3..:..#..@...
    0030 - 05 ea f5 5e 94 4b bb 33-54 ab 46 f1 0c e8 b0 b7   ...^.K.3T.F.....
    0040 - 52 e3 51 e1 20 d6 9f 58-c6 40 5f 11 58 e1 dd de   R.Q. ..X.@_.X...
    0050 - db 05 3c 69 74 38 3b 6e-3f 93 21 bb 1d 4e 48 4a   ..<it8;n?.!..NHJ
    0060 - cf 19 f1 fd ec ac 0b e3-93 b4 4e 12 d1 03 61 9a   ..........N...a.
    0070 - 24 d6 c8 13 19 ba cd 9c-5a 1d 0c da ab e3 c5 b2   $.......Z.......
    0080 - 2d 79 f2 91 31 29 08 32-c7 1b c5 ef 89 bf fb db   -y..1).2........
    0090 - e4 66 2b a8 bb e3 23 76-ac a1 83 bb 4a 5f 4b 6c   .f+...#v....J_Kl
    00a0 - 6d 36 e2 71 ac 68 23 4b-de 6f 5c d7 b1 8c d1 5c   m6.q.h#K.o\....\

    Start Time: 1591927401
    Timeout   : 7200 (sec)
    Verify return code: 0 (ok)
    Extended master secret: yes

I think this proves that the included openssl that comes with Pythonista (which ssl.py sources) needs to be upgraded to a later version

JonB

I wonder if the cert authority that certified your server is trusted by your iOS version.

See
https://support.apple.com/en-us/HT210770

You may be able to install the server cert directly onto your device to trust it implicitly.

Have you looked at the change logs between those two openssl versions? Might give a hint as to what is wrong.

samaklis

Thanks for the feedback.

Not sure how exactly to interpret the below but below is what I get back as the "Issuer" information from my certificate. COMODO Certification Authority seems to be trusted based on the list in the link you provided.

CN = COMODO RSA Domain Validation Secure Server CA
O = COMODO CA Limited
L = Salford
S = Greater Manchester
C = GB

In regards to the openssl changes, they are quite extensive (4 years) worth, and I am not sure I can quite pick out what change may have had an adverse effect, although I did go through their CHANGES file.

Wouldn't the fact that I can replicate the issue outside of Pythonista "prove" that this is not specific to iOS but specific to the openssl version used by it?

PrivateTech

Does anybody know what's going on with SSL certificate errors in Pythonista on iPhone?

EDIT: This very forum page on omz-software.com shows a certificate error in Google Chrome on a desktop.

I tried the simplest code to retrieve a small plain text web page. I tried the same code on iPhone in Pythonista and in Pyto. Tried many other pages too.

Pyto works fine every time.

Pyntonosta fails with error message on some web sites but not others.

I think I’ve identified a pattern. Pythonista breaks on web sites with Let’s Encrypt SSL Certificate.

Even stranger behavior is that some pages fail on some days but the very same pages seem to return no errors on another day when I tested again. And back to errors again a day later.

I contacted omz-software (omz:software) support via email a few days ago but haven’t heard from them yet.

The script is extremely simple:

with urllib.request.urlopen(URL) as response:
     html = response.read()

The error I get:

urllib.error.URLError: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:749)

/var/containers/Bundle/Application/08EAF123-C40E-4CCA-98BE-395691A7AC9D/Pythonista3.app/Frameworks/Py3Kit.framework/pylib/urllib/request.py", line 1321, in do_open

var/containers/Bundle/Application/08EAF123-C40E-4CCA-98BE-395691A7AC9D/Pythonista3.app/Frameworks/Py3Kit.framework/pylib/urllib/request.py", line 1362, in https_open
context=self._context, check_hostname=self._check_hostname)

Any Ideas?

It is also posed here in case if someone responds there as well

omz

@PrivateTech I'll look into it. The workaround in this StackOverflow answer should also work in Pythonista.