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NDSS 2017 - Session 4A: TLS et al.

Session Chair:  Johanna Amann

Measuring small subgroup attacks against Diffie-Hellman

Several recent standards, including NIST SP 800- 56A and RFC 5114, advocate the use of    DSA    parameters for Diffie-Hellman key exchange. While it is possible to use such parameters securely, additional validation checks are necessary to prevent well-known and potentially devastating attacks. In this paper, we observe that many Diffie-Hellman implementations do not properly validate key exchange inputs. Combined with other protocol properties and implementation choices, this can radically decrease security. We measure the prevalence of these parameter choices in the wild for HTTPS, POP3S, SMTP with STARTTLS, SSH, IKEv1, and IKEv2, finding millions of hosts using DSA and other non-   safe    primes for Diffie-Hellman key exchange, many of them in combination with potentially vulnerable behaviors. We examine over 20 open-source cryptographic libraries and applications and observe that until January 2016, not a single one validated subgroup orders by default. We found feasible full or partial key recovery vulnerabilities in OpenSSL, the Exim mail server, the Unbound DNS client, and Amazon   s load balancer, as well as susceptibility to weaker attacks in many other applications. 

Authors:     Luke Valenta (University of Pennsylvania)
                  David Adrian (University of Michigan)
                  Antonio Sanso (Adobe)
                  Shaanan Cohney (University of Pennsylvania)
                  Joshua Fried (University of Pennsylvania)
                  Marcella Hastings (University of Pennsylvania)
                  J. Alex Halderman (University of Michigan)
                 Nadia Heninger (University of Pennsylvania)

Indiscreet Logs: Diffie-Hellman Backdoors in TLS

Software implementations of discrete logarithm based cryptosystems over finite fields typically make the assumption that any domain parameters they encounter define cyclic groups for which the discrete logarithm problem is assumed to be hard. In this paper we explore this trust assumption and examine situations where it may not be justified. In particular we focus on groups for which the order is unknown and not easily determined, and explore the scenario in which the modulus is trapdoored to make computing discrete logarithms efficient for an entity with knowledge of the trapdoor, while simultaneously leaving its very existence as matter of speculation to everyone else. 

We conducted an investigation of discrete logarithm domain parameters in use across the Internet and discovered a multitude of instances of groups of unknown order in use in TLS and STARTTLS spanning numerous countries, organizations, and implementations. Although our disclosures resulted in a number of organizations taking down their suspicious parameters, none were able or willing to rule out the possibility that their parameters were trapdoors, and obtaining conclusive evidence in each case could be as hard as factoring an RSA modulus, highlighting a key feature of this attack method   deniability. 

Authors:     Kristen Dorey (Western University)
                  Nicholas Chang-Fong (Western University)
                  Aleksander Essex (Western University)

WireGuard: Next Generation Kernel Network Tunnel

WireGuard is a secure network tunnel, operating at layer 3, implemented as a kernel virtual network interface for Linux, which aims to replace both IPsec for most use cases, as well as popular user space and/or TLS-based solutions like OpenVPN, while being more secure, more performant, and easier to use. The virtual tunnel interface is based on a proposed fundamental principle of secure tunnels: an association between a peer public key and a tunnel source IP address. It uses a single round trip key exchange, based on NoiseIK, and handles all session creation transparently to the user using a novel timer state machine mechanism. Short pre-shared static keys   Curve25519 points    are used for mutual authentication in the style of OpenSSH. The protocol provides strong perfect forward secrecy in addition to a high degree of identity hiding. Transport speed is accomplished using ChaCha20Poly1305 authenticated-encryption for encapsulation of packets in UDP. An improved take on IP-binding cookies is used for mitigating denial of service attacks, improving greatly on IKEv2 and DTLS   s cookie mechanisms to add encryption and authentication. The overall design allows for allocating no resources in response to received packets, and from a systems perspective, there are multiple interesting Linux implementation techniques for queues and parallelism. Finally, WireGuard can be simply implemented for Linux in less than 4,000 lines of code, making it easily audited and verified. 

Authors:     Jason A. Donenfeld

The Security Impact of HTTPS Interception

As HTTPS deployment grows, middlebox and antivirus products are increasingly intercepting TLS connections to retain visibility into network traffic. In this work, we present a comprehensive study on the prevalence and impact of HTTPS interception. First, we show that web servers can detect interception by identifying a mismatch between the HTTP User-Agent header and TLS client behavior. We characterize the TLS handshakes of major browsers and popular interception products, which we use to build a set of heuristics to detect interception and identify the responsible product. We deploy these heuristics at three large network providers: (1) Mozilla Firefox update servers, (2) a set of popular e-commerce sites, and (3) the Cloudflare content distribution network. We find more than an order of magnitude more interception than previously estimated and with dramatic impact on connection security. To understand why security suffers, we investigate popular middleboxes and clientside security software, finding that nearly all reduce connection security and many introduce severe vulnerabilities. Drawing on our measurements, we conclude with a discussion on recent proposals to safely monitor HTTPS and recommendations for the security community. 

Authors:     Zakir Durumeric (University of Michigan, ICSI)
                  Zane Ma (University of Illinois Urbana-Champaign)
                  Drew Springall (University of Michigan)
                  Richard Barnes (Mozilla)
                  Nick Sullivan (CloudFlare)
                  Elie Bursztein (Google)
                  Michael Bailey (Univ. of Illinois Urbana-Champaign)
                  J. Alex Halderman (University of Michigan)
                 Vern Paxson (UC Berkeley, ICSI)