Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Investigating Mobile Messaging Security Elias Hazboun 27/4/2016 Chair for Network Architectures and Services Department of Informatics Technische Universit¨ at M¨ unchen E. Hazboun – Investigating Mobile Messaging Security 1
Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Motivation Introduction Research Question App Selection Background Approach Security background Related Work Analysis and Results TextSecure Threema WeChat WhatsApp Conclusion E. Hazboun – Investigating Mobile Messaging Security 2
Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Introduction ◮ Mobile messaging apps have become very popular. ◮ People are opting to communicate using the Internet instead of sending messages over regular cellular networks. ◮ Unlike Email and other communication protocols, most apps are closed systems. ◮ Hinders interoperability [1]. ◮ No transparency in handling users’ data. ◮ Users are still not well informed about the risks of non-secure digital communication [2]. E. Hazboun – Investigating Mobile Messaging Security 3
Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Research Question ◮ Investigate the security properties of a selection of today’s most popular mobile messaging apps in terms of: ◮ Encryption & Authentication. ◮ Standardized security protocol usage. E. Hazboun – Investigating Mobile Messaging Security 4
Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen App Selection ◮ Continuation of work done in this chair [3]. ◮ Security in relation to users’ geo-location. ◮ Selection was based on popularity, security measures, architecture and geographical server distribution. ◮ Tested apps were: ◮ WhatsApp ◮ Threema ◮ WeChat ◮ TextSecure E. Hazboun – Investigating Mobile Messaging Security 5
Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Approach ◮ Investigating: ◮ Official app documentation ◮ Past research efforts, from scientific community and hackers. ◮ Could be obsolete by newer updates. ◮ Network traffic analysis. ◮ Capture process done by the previous work using two communicating smartphones. ◮ 407 capture files per smartphone per app. ◮ Manual and automated script analysis. E. Hazboun – Investigating Mobile Messaging Security 6
Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Layers of Encryption E. Hazboun – Investigating Mobile Messaging Security 7
Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Security Concepts ◮ Perfect Forward Secrecy (PFS) ◮ Compromise of long-term keys used to negotiate session keys, does not compromise the secrecy of past session keys. ◮ Most commonly achieved using ephemeral Diffie-Hellman (DH) key exchange [4]. ◮ Important against an attacker model that can store arbitrary amount of traffic, like governments. ◮ Transprot Layer Protocol (TLS) ◮ De facto Standard protocol for security between client and server on the Internet. E. Hazboun – Investigating Mobile Messaging Security 8
Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Security Concepts ◮ Certificate Pinning ◮ Insertion of public key or certificate of the entity with which a software should communicate in the source code. ◮ Removes need to trusted third party certificate authorities. ◮ Asynchronous Messaging Security: ◮ Not all parties are guaranteed to be online at the same time to perform key exchange [5]. ◮ Creates a challenge. Protocols like OpenPGP are used but they lack PFS. ◮ Trusted third parties for key distribution can be used. E. Hazboun – Investigating Mobile Messaging Security 9
Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Related Work ◮ Interest has been growing in the past few years, especially in the public eye. ◮ Focus of research include: ◮ Authentication process when registering [6]. ◮ Receiving unsolicited messages. ◮ Phonebook enumeration. ◮ Local security (security of data on smartphone) [7] [8]. ◮ Network traffic based analysis [9] [10]. ◮ Results show a trend of negligence of security from developers, but gets better with app updates. E. Hazboun – Investigating Mobile Messaging Security 10
Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen TextSecure ◮ Developed by Open Whisper Systems in 2010. ◮ Only app out of four to be open Source. ◮ End-to-end encryption and hardened security in general as selling feature. ◮ Discontinued and replaced by Signal app and Signal protocol. ◮ Direct code inspection due to open source nature. ◮ Forsch et al [11] found some peculiarities such as unknown key-share attack. ◮ Developers acknowledged it. E. Hazboun – Investigating Mobile Messaging Security 11
Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Analysis and Results ◮ End-to-end encryption. ◮ Axolotl ratchet (DH ratchet and key derivation based ratchet). ◮ Guarantees PFS and backward secrecy. ◮ DH ratchet creates keys used for session keys, which are then used to seed key derivation based ratchets to create keys to encrypt messages [12]. ◮ Transport layer encryption. ◮ TLS with self-signed certificate pinning. (The same in all captures) [13]. ◮ Cipher was ECDHE RSA WITH AES 128 GCM SHA256. E. Hazboun – Investigating Mobile Messaging Security 12
Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Analysis and Results ◮ When an App registers it: ◮ Creates 100 prekeys (signed key exchange messages) [14]. ◮ Sends them to server. ◮ When a user wants to communicate with another: ◮ Sender asks for next valid prekey. ◮ Calculates a shared secret based on it and encrypts messages with it. ◮ AES is used for symmetric encryption. ◮ Two levels of symmetric encryption are used to protect the sender’s identity from Google Cloud Messaging server. E. Hazboun – Investigating Mobile Messaging Security 13
Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Threema ◮ Developed by Threema GmbH, Popular in German speaking countries. ◮ Promises end-to-end encryption and data hosting on swiss based servers. ◮ Partly open source, publishes white paper about security algorithms. ◮ Allowed an external security audit of the app. ◮ Jan Ahrens [15] provided an analysis on Threema protocol. ◮ Dimitrov, Laan and Pineda [16] analysis demonstrated with high probability that certificate pinning is present. E. Hazboun – Investigating Mobile Messaging Security 14
Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Analysis and Results ◮ Handshake process is similar to what is described in related work [15]. ◮ No standardized protocol use. ◮ Binary protocol implemented using NaCl Library. ◮ Directory service and media transfer protocol use HTTPS. Cipher suite was in all capture files: ECDHE RSA WITH AES 256 GCM SHA384. ◮ PFS only on transport layer, not end-to-end [17]. ◮ Random padding is used. ◮ Messages with same plaintext size are encrypted into differently sized ciphertexts. E. Hazboun – Investigating Mobile Messaging Security 15
Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Analysis and Results Threema End-to-End Encryption [17] E. Hazboun – Investigating Mobile Messaging Security 16
Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen WeChat ◮ Developed by Tenecent. ◮ One of the largest messaging apps by monthly active users (over 650 million) ◮ Feature rich app offering lots of additions. ◮ Closed source, but has public API for messaging through the service. ◮ Roberto Paleari [18] performed network traffic analysis. ◮ It uses a custom protocol similar to HTTPS E. Hazboun – Investigating Mobile Messaging Security 17
Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen Analysis and Results ◮ Even DNS queries are peformed over HTTP [3]. ◮ Uses AES for symmetric encryption. ◮ No indication for the existence of end-to-end encryption or PFS. ◮ Key derivation is suspected to be done using RSA [18]. ◮ Could not verify ourselves. ◮ Out of the 4 apps. WeChat is the more obscure and more secretive in terms of security mechanisms and protocols. E. Hazboun – Investigating Mobile Messaging Security 18
Chair for Network Architectures and Services Technische Universit¨ at M¨ unchen WhatsApp ◮ Developed by WhatsApp Inc. (bought by Facebook) ◮ Second most popular messaging app in the world (1 billion users) ◮ Closed source. ◮ Past research found lots of deficiencies [6] [19]. ◮ Started as plaintext. Upgraded to weak encryption [20] [21]. ◮ non-secure user registration process. ◮ Funcional clone projects exist [22] [23]. Almost complete replicas. E. Hazboun – Investigating Mobile Messaging Security 19
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