defeating whatsapp’s lack of encryption - bh sao paulo 2013

DEFEATING WHATSAPP’S

Defeating`s

Lack of Privacy

Defeating WhatsApp’s Lack of Privacy

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WHO WE AREJaime Sánchez

- Computer Engineer & Security Researcher - Executive MBA, CISSP, CISA and CISM - Speaker at Rootedcon, Nuit du Hack, BH Arsenal, Defcon, DerbyCon, NoConName, DeepSec etc. - Twitter : @segofensiva - http://www.seguridadofensiva.com

!!Pablo San Emeterio

- Computer Engineer / I+D Optenet - Master of Science in Computer Security by UPM, CISA and CISM - Speaker at NoConName and CiberSeg - Previous experience with WhatsApp :) - Twitter : @psaneme

http://www.seguridadofensiva.com


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CONGRATS PABLO! :)

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- WhatsApp is a cross-platform (no desktop clients) instant messaging subscr iption ser vice for smartphones, that let users send messages and multimedia files to each other. !- Because it uses your internet data plan and there's no additional cost for these messages, it's mostly used young people. !- Was founded in 2009 by American Brian Acton and Ukrainian Jan Koum (also the CEO), both former employees of Yahoo!, and is based in Santa Clara, California. !- WhatsApp might not be as widely known as Twitter, but it is definitely just as popular in terms of users.

¿ WHAT IS WHATSAPP ?

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USERS STATS

It’s interesting to compare that stat to Twitter, which has 230 million active monthly users, and to Instagram, which has 150 million on its platform.

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MESSAGE STATS

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Just how much is 10 billion messages?

416,666,670 messages an hour

6,944,440 messages a minute

115,704 messages a second

- WhatsApp has done to SMS on mobile phones what Skype did to international calling on landlines!

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NoConName 2013Black Hat Sao Paulo

Hardware Specs - Dual octo-core E5-2690 (32 logical CPUs) - 256GB RAM (128GB for A/V hosts) - 6 x 800GB SSD (4TB SATA for A/V hosts) - 2 x dual link-agg gig-E (public, private) !New features - Resumable uploads and downloads - Reference counting

Peak Scalability - 214M images in a day - 8.8K images/sec downloaded - 29 Gb/sec output bandwidth !

NEW ARCHITECTURE

Holiday Week


NoConName 2013

SECURITY FLAWS- WhatsApp communications were not encrypted, and data was sent and received in plaintext, meaning messages to easily be read if packet traces are available (WhatsApp Sniffer) !- WhatsApp began using IMEI numbers and MAC addresses as passwords. !- Remote storage of virus, programs, html etc. on WhatsApp servers !- Critical flaw lead to control any account (modify account, send and receive messages etc.) !- Data stored in plaintext on database !- An unknown hacker published a website (WhatsAppStatus.net) that made it possible to change the status of an arbitrary WhatsApp user, as long as the phone number was known. (To make it work, it only required a restart of the app)

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NoConName 2013

MORE SECURITY FLAWS- On January 13, 2012, WhatsApp was pulled from the iOS App Store, and the reason was not disclosed. The app was added back to the App Store four days later !- Priyanka appeared spreading on Whatsapp through a contacts file that if you add to your contacts. !- WhatsApp Voyeur: allows you to view the profile picture and current "Status" of every user without using a mobile phone or registered account !- No authorization required to send messages, so any user can contact you or any custom designed bot could be created to send you spam. !- Serious WhatsApp flaw allows decrypting user messages !!!- This is what we know so far ...

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BLOCKING- Saudi Arabia plans to block Internet-based communication tool WhatsApp within weeks if the U.S.-based firm fails to comply with requirements set by the kingdom's telecom regulator, local newspapers reported this week. !- This month the Communications and Information Technology Commission (CITC) banned Viber, another such tool, which like WhatsApp is hard for the state to monitor and deprives telecom companies of revenue from international calls and texts. !- The regulator issued a directive saying tools such as Viber, WhatsApp and Skype broke local laws, without specifying how.

http://www.reuters.com/article/2013/06/16/us-saudi-internet-idUSBRE95F04R20130616

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http://www.reuters.com/article/2013/06/16/us-saudi-internet-idUSBRE95F04R20130616


NoConName 2013

SURVEILLANCE- Reports and documents leaked by Edward Snowden in June 2013 indicate that PRISM is used for monitoring communications and other stored information. !- The data that the NSA is supposedly able to get by PRISM includes email, video, voice chat, photos, IP addresses, login notifications, file transfer and details about social networking profiles. !- Internet companies such as Microsoft, Google, Yahoo, Dropbox, Apple and Facebook are inside the program. !- The objectives of the PRISM program are those citizens living outside the United States, but U.S. citizens are included too.

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NoConName 2013

¿ Could WhatsApp be one of these companies ?

The NSA infected more than 50,000 computers worldwide with malicious software designed to steal confidential

information. Some countries affected are Venezuela, Bolivia, Brazil, Ecuador, Cuba, Colombia and Honduras, among others.

The attacks are performed by a special department called Tailored Access Operations (TAO), which has more than a

thousand hackers.

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THE IDEA

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- The main objective of the research is to add a new layer of security and privacy to ensure that in the exchange of messages between members of a conversation both the integrity and confidentiality could not be affected by an external attacker :

GOALS

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- Add secure encryption to the client. If an attacker intercepts the messages, or any governments try to intercept our messages at WhatsApp's server , they won't find any legible information. - Give a certain level of anonymity to the conversation by using fake/anonymous accounts and intermediate communication nodes. - Modify the inner workings of the appl icat ion , rout ing a l l t r a ffic and conversation messages to own server (XMPP).


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- This technique has been developed to be used in a manner completely transparent to the users. !- The software works for all WhatsApp’s platforms: we have developed a Linux-based solution (it works inside a Raspberry Pi, your laptop computer or you could use a VPN). !- Could be ported to run inside Android.

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GOALS


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INSIDE THE WORLD OF WHATSAPP

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FUNXMPP- WhatsApp uses a customized version of the open standard eXtensible Messaging and Presence Platform (XMPP), called FunXMPP, that uses XML as its syntax.. !- Without going into technical details, it is a messaging protocol that uses XML syntax: !

<message from=”[email protected]” id=”1339831077-7” type=”chat” timestamp=”1339848755”> <notify xmlns=”urn:xmpp:whatsapp” name=”NcN” /> <request xmlns=”urn:xmpp:receipts” /> <body>Hello</body> </message>

!- Since WhatsApp is intended for mobile devices, they wanted to use as little overhead as possible. !- ¿ How did they achieve this ?

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mailto:[email protected]


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FUNXMPP- First of all, all keywords are assigned a byte each. If you can replace each by just one byte, it would reduce the overhead a lot. !- FunXMPP uses a HashTable for this, containing most (if not all) keywords !- Given the syntax \xnn for one byte with the hexadecimal value nn, the example above could be reduced to the following: !

<\x5d \x38=”01234567890@\x8a” \x43=”1339831077-7” \xa2=”\x1b” \x9d=”1339848755”> <\x65 \xbd=”\xae” \x61=”NcN” /> <\x83 \xbd=”\xad” /> <\x16>Hello</\x16> </\x5d> !

- All remaining ascii values cannot be replaced by a representative byte-value, because they are variable/no fixed keywords.

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BYTES- Byte \xfc: This byte signifies a sequence of ascii characters will be used as the value. The length of this sequence can be found in the next byte (max length 255). - Byte \xfd: Where \xfc reads one byte for the length,\xfd reads three bytes. This allows for strings up to a max of 16777215 characters. - Byte \xf8 y \xf9: Declare the beginning of a list and it is followed by its number of elements and subsequently the content,.

The way members are counted is: ! 1 2 3 <message from=”[email protected]” 4 5 id=”1339831077-7” 6 7 type=”chat” 8 9 timestamp=”1339848755”> <notify xmlns=”urn:xmpp:whatsapp” | name=”NcN” /> | 10 <request xmlns=”urn:xmpp:receipts” /> | <body>Hello</body> |

</message>

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mailto:[email protected]


NoConName 2013

57:41 => WA 01:02 => PROTOCOL VERSION 1.2 !f8:05:01:c8:ab:a5:fc:12:69:50:68:6f:6e:65:2d:32:2e:31:30:2e:32:2d:35:32:32:32:00:00 0x01 => stream:stream 0xc8 => to 0xab: s.whatsapp.net 0xa5 => resource 0xfc => String 12caracteres => iPhone-2.10.2-5222 <stream:stream to=”s.whatsapp.net” resource=”iPhone-2.10.2-5222” /> !

f8:02:bb => 0xbb => stream:features f8:04 f8:03:70:31:ca => 0x70 => message_acks 0x31 => enable 0xca => TRUE f8:01:9c => 0x9c => receipt_acks f8:03:e4:cb:0c => 0xe4 => w:profile:picture 0xcb => type 0x0c => all f8:03:b9:7c:ca => 0xb9 => status 0x7c => notification 0xca => TRUE <stream:features> <message_acks enable=TRUE /> <receipt_acks /> <w:profile:picture type=ALL /> <status notification=TRUE /> </stream:features> !

f8:08:10:6d:ec:da:fc:0b:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:X:e8:cf 0x10 => auth 0x6d => mechanism 0xec => WAUTH-1 user => 34XXXXXXXXX 0x31 => enable 0xe8 => xmlns 0xcf => urn:ietf:params:xml:ns:xmpp-sasl <auth mechanism=”WAUTH-1” user=”XXXXXXXXXXX” xmlns=”urn:ietf:params:xml:ns:xmpp-sasl” />

LOGIN

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http://s.whatsapp.net/


NoConName 2013

LOGGING IN ON A NEW DEVICE1) WhatsApp will send the user’s phone number to servers, through HTTPS, requesting an authentication code 2) The mobile phone receives, through text message, the authentication code 3) This authentication code is sent and compared, and if matches, WhatsApp obtains the password !

- To log in, the client uses a custom SASL mechanism, called WAUTH-1. First, the client sends:

<auth xmlns="urn:ietf:params:xml:ns:xmpp-sasl" user="XXXXXXXXXXXX" mechanism="WAUTH-1" /> !

- Server will answer with a challenge: <challenge xmlns="urn:ietf:params:xml:ns:xmpp-sasl">YYYYYYYYYYYYYYYYYYYY </challenge> !

- To respond the challenge, the client will generate a key using PKBDF2 with user’s password, challenge as salt and SHA1 as hash function. Only 20 bytes from result will be used as key <phone number> || <20 bytes> || UNIX timestamp:

<response xmlns="urn:ietf:params:xml:ns:xmpp-sasl">ZZZZZZZZZZZZZ</response>

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ARE MY MESSAGES SECURE ?

- RC4, the most widely used software stream cipher and is used in popular protocols such as Transport Layer Security (TLS) and WEP, was designed by Ron Rivest of RSA Security in 1987 !- RC4 has two stages - a KSA, that initializes the state table to be a "random" permutation based on the key, and the PRGA, which actually returns a random byte.

¿ Where is the problem ?

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From the creators of: - Don't run with scissors - Don't run near the pool - Don't run near the pool while carrying scissors !!Now comes:

DON’T re-use the same RC4 keystream to encrypt two different messages

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EVERY TIME ALICE ENCRYPTS A MESSAGE

Suppose Alice wants to send encryptions of m1 and m2 to Bob over a public channel. Alice and Bob have a shared key k; however, both messages are the same length as the key k. Since Alice is extraordinary lazy (and doesn't know about stream ciphers), she decides to just reuse the key. !Alice sends ciphertexts c1 = m1 ⊕ k and c2 = m2 ⊕ k to Bob through a public channel. Unfortunately, Eve intercepts both of these ciphertexts and calculates c1 ⊕ c2= m1 ⊕ m2.

c1 = m1 ⊕ k c2 = m2 ⊕ k

c1 ⊕ c2 = m1 ⊕ m2

m1 = c1 ⊕ k m2 = c2 ⊕ k

REUSED KEY ATTACK

, GOD KILLS A KITTEN ...

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ATTACKING WHATSAPP’S ENCRYPTION- From here, the task becomes separating the two plaintexts from one another (plaintext attack or Crib-Dragging), following the steps bellow: 1) Guess a word that might appear in one of the messages 2) Encode the word from step 1 to a hex string 3) XOR the two cipher-text messages 4) XOR the hex string from step 2 at each position of the XOR of the two cipher-texts (from step 3) 5) When the result from step 4 is readable text, we guess the English word and expand our crib search. 6) If the result is not readable text, we try an XOR of the crib word at the next position. !- To do this, we have to do a little guessing about the plaintexts themselves. !- The idea is to use a Frecuency Analysis based on the original language used in the plaintext.

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NoConName 2013

"WhatsApp takes security seriously and is continually thinking of ways to improve our product. While we appreciate feedback, we're concerned that the blogger's story describes a scenario that is more theoretical in nature. Also stating that all conversations should be considered compromised is inaccurate" the company said.

WTF!Official response to https://blog.thijsalkema.de/blog/2013/10/08/piercing-through-whatsapp-s-encryption/

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https://blog.thijsalkema.de/blog/2013/10/08/piercing-through-whatsapp-s-encryption/



-‐ DEMO -‐


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ANONYMITY

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VIRTUAL NUMBERS

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ADDITIONAL ENCRYPTION

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INTERCEPT MESSAGES- We have verified that the encryption used to protect the information and privacy of our conversations is easy to break. !- ¿What can we do? We will intercept WhatsApp's message before you leaving the mobile phone. We'll decipher the original message with our key and we will apply a new cipher and then encrypt it with the original algorithm and key, not breaking the application. !- From now on, we’ll be working this way:

REAL-TIME MODIFICATION

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CHALLENGE AND iOS

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- In iOS version we’ll use a little trick to get the challenge. Instead of exchanging it during the log-in, WhatsApp sends the challenge for the next session while connected. !- We’ll flip some random bytes, forcing WhatsApp to negotiate it again:

- The result for the log in of the second mobile is the same:


NoConName 2013

- You can see how our program has decoded the original message: Bello !- HMAC is deleted in the decoded message and we calculate it again before sending. Finally, the message will leave our mobile phone. We can see that the new message is different from the original because is has a layer encryption implemented by us:

SENDING MESSAGES

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- The message is sent from the client. Our program detects it, and using the RC4 session key used by WhatsApp, decrypts the message and extracts text. Once the text is clear, encrypts it with our algorithm and key, and re-wrap it in the original format with RC4 encryption it again, not breaking the operation of WhatsApp:

HMAC


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- In the screenshot you can see how we received an normal WhatsApp message, but it’s really special. When we use the RC4 key to decrypt the text inside, we find is completely unreadable.

- Using the same private key and algorithm, our program will decrypt the message text and reassemble the original text, so WhatsApp will be able to process it. !!- The final message can be read as usually by the user, and it’s the same as the first one:

RECEIVING MESSAGES

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-‐ DEMO -‐


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WITHOUT PRIVATE KEY

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EXTERNAL XMPP SERVER

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HIDING OUR MESSAGES

- The above method allows us to encrypt our messages, so other attackers capable of intercepting our traffic will not be able to get the contents of messages. !- But, ¿ what if we want the traffic to directly bypass the WhatsApp's server ?

EXTERNAL XMPP SERVER

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NoConName 2013

USING AN EXTERNAL XMPP SERVER- We analyze the outgoing message and decrypt it using the RC4 key. !- Then, we extract the original text and send it to our external XMPP server :

<destination number>¿<message_id>¿<original text>

- The program will replace every character in the original text with our wildcard character, so the original message will never pass through WhatsApp's servers (this step is necessary or destination will reject our messages) !- Recipient receives our message full of wildcard characters, querys our XMPP server and replaces the wildcard characters with the original text.

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-‐ DEMO -‐


NoConName 2013

WHATSAPP CAN ONLY SEE ...

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