Emilia Kasper
Emilia joined Google in 2011 and is currently part of the Information Security Engineering team where she focuses on secure API design. She is a co-author of Google's Certificate Transparency proposal and a member of the OpenSSL development team. She has published papers on high-speed cryptography and holds a PhD from KU Leuven, Belgium.
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DROWN: Breaking TLS using SSLv2
Christoph Paar
David Adrian
J. Alex Halderman
Jens Steube
Juraj Somorovsky
Luke Valenta
Maik Dankel
Nadia Heninger
Nimrod Aviram
Sebastian Schinzel
Shaanan Cohney
Susanne Engels
Viktor Dukhovni
Yuval Shavitt
25th USENIX Security Symposium (2016)
Preview abstract
We present DROWN, a novel cross-protocol attack that
can decrypt passively collected TLS sessions from upto-date
clients by using a server supporting SSLv2 as a
Bleichenbacher RSA padding oracle. We present two versions
of the attack. The more general form exploits a combination
of thus-far unnoticed protocol flaws in SSLv2
to develop a new and stronger variant of the Bleichenbacher
attack. A typical scenario requires the attacker
to observe 1,000 TLS handshakes, then initiate 40,000
SSLv2 connections and perform 2
50 offline work to decrypt
a 2048-bit RSA TLS ciphertext. (The victim client
never initiates SSLv2 connections.) We implemented the
attack and can decrypt a TLS 1.2 handshake using 2048-
bit RSA in under 8 hours using Amazon EC2, at a cost
of $440. Using Internet-wide scans, we find that 33% of
all HTTPS servers and 22% of those with browser-trusted
certificates are vulnerable to this protocol-level attack,
due to widespread key and certificate reuse.
For an even cheaper attack, we apply our new techniques
together with a newly discovered vulnerability in
OpenSSL that was present in releases from 1998 to early
2015. Given an unpatched SSLv2 server to use as an
oracle, we can decrypt a TLS ciphertext in one minute on
a single CPU—fast enough to enable man-in-the-middle
attacks against modern browsers. 26% of HTTPS servers
are vulnerable to this attack.
We further observe that the QUIC protocol is vulnerable
to a variant of our attack that allows an attacker to
impersonate a server indefinitely after performing as few
as 225 SSLv2 connections and 265 offline work.
We conclude that SSLv2 is not only weak, but actively
harmful to the TLS ecosystem.
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The Dangers of Composing Anonymous Channels
George Danezis
Information Hiding - 14th International Conference, IH 2012, Revised Selected Papers, Springer, Lecture notes in Computer Science (2013), pp. 191-206
Preview abstract
We present traffic analyses of two anonymous communications schemes that build on the classic Crowds/Hordes protocols. The AJSS10 [1] scheme combines multiple Crowds-like forward channels with a Hordes reply channel in an attempt to offer robustness in a mobile environment. We show that the resulting scheme fails to guarantee the claimed k-anonymity, and is in fact more vulnerable to malicious peers than Hordes, while suffering from higher latency. Similarly, the RWS11 [15] scheme invokes multiple instances of Crowds to provide receiver anonymity. We demonstrate that the sender anonymity of the scheme is susceptible to a variant of the predecessor attack [21], while receiver anonymity is fully compromised with an active attack. We conclude that the heuristic security claims of AJSS10 and RWS11 do not hold, and argue that composition of multiple anonymity channels can in fact weaken overall security. In contrast, we provide a rigorous security analysis of Hordes under the same threat model, and reflect on design principles for future anonymous channels to make them amenable to such security analysis.
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Fast Elliptic Curve Cryptography in OpenSSL
Financial Cryptography and Data Security: FC 2011 Workshops, RLCPS and WECSR, Springer
Preview abstract
We present a 64-bit optimized implementation of the NIST and SECG-standardized elliptic curve P-224. Our implementation is fully integrated into OpenSSL 1.0.1: full TLS handshakes using a 1024-bit RSA certificate and ephemeral Elliptic Curve Diffie-Hellman key exchange over P-224 now run at twice the speed of standard OpenSSL, while atomic elliptic curve operations are up to 4 times faster. In addition, our implementation is immune to timing attacks - most notably, we show how to do small table look-ups in a cache-timing resistant way, allowing us to use precomputation. To put our results in context, we also discuss the various security performance trade-offs available to TLS applications.
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