On the Post-Quantum Security of Classical Authenticated Encryption Schemes

We study the post-quantum security of authenticated encryption (AE) schemes, designed with classical security in mind. Under superposition attacks, many CBC-MAC variants have been broken, and AE modes employing those variants, such as EAX and GCM, thus fail at authenticity. As we show, the same modes are IND-qCPA insecure, i.e., they fail to provide privacy under superposition attacks. However, a constrained version of GCM is IND-qCPA secure, and a nonce-based variant of the CBC-MAC is secure under superposition queries. Further, the combination of classical authenticity and classical chosen-plaintext privacy thwarts attacks with superposition chosen-ciphertext and classical chosen-plaintext queries -a security notion that we refer to as IND-qdCCA. And nonce-based key derivation allows generically turning an IND-qdCCA secure scheme into an IND-qCCA secure scheme

Using Simon's Algorithm to Attack Symmetric-Key Cryptographic Primitives

We present new connections between quantum information and the field of classical cryptography. In particular, we provide examples where Simon's algorithm can be used to show insecurity of commonly used cryptographic symmetric-key primitives. Specifically, these examples consist of a quantum distinguisher for the 3-round Feistel network and a forgery attack on CBC-MAC which forges a tag for a chosen-prefix message querying only other messages (of the same length). We assume that an adversary has quantum-oracle access to the respective classical primitives. Similar results have been achieved recently in independent work by Kaplan et al. Our findings shed new light on the post-quantum security of cryptographic schemes and underline that classical security proofs of cryptographic constructions need to be revisited in light of quantum attackers.Comment: 14 pages, 2 figures. v3: final polished version, more formal definitions adde

Stacco: Differentially Analyzing Side-Channel Traces for Detecting SSL/TLS Vulnerabilities in Secure Enclaves

Intel Software Guard Extension (SGX) offers software applications enclave to protect their confidentiality and integrity from malicious operating systems. The SSL/TLS protocol, which is the de facto standard for protecting transport-layer network communications, has been broadly deployed for a secure communication channel. However, in this paper, we show that the marriage between SGX and SSL may not be smooth sailing. Particularly, we consider a category of side-channel attacks against SSL/TLS implementations in secure enclaves, which we call the control-flow inference attacks. In these attacks, the malicious operating system kernel may perform a powerful man-in-the-kernel attack to collect execution traces of the enclave programs at page, cacheline, or branch level, while positioning itself in the middle of the two communicating parties. At the center of our work is a differential analysis framework, dubbed Stacco, to dynamically analyze the SSL/TLS implementations and detect vulnerabilities that can be exploited as decryption oracles. Surprisingly, we found exploitable vulnerabilities in the latest versions of all the SSL/TLS libraries we have examined. To validate the detected vulnerabilities, we developed a man-in-the-kernel adversary to demonstrate Bleichenbacher attacks against the latest OpenSSL library running in the SGX enclave (with the help of Graphene) and completely broke the PreMasterSecret encrypted by a 4096-bit RSA public key with only 57286 queries. We also conducted CBC padding oracle attacks against the latest GnuTLS running in Graphene-SGX and an open-source SGX-implementation of mbedTLS (i.e., mbedTLS-SGX) that runs directly inside the enclave, and showed that it only needs 48388 and 25717 queries, respectively, to break one block of AES ciphertext. Empirical evaluation suggests these man-in-the-kernel attacks can be completed within 1 or 2 hours.Comment: CCS 17, October 30-November 3, 2017, Dallas, TX, US

Key-Reduced Variants of 3kf9 with Beyond-Birthday-Bound Security

3kf9 is a three-key CBC-type MAC that enhances the standardized integrity algorithm f9 (3GPP-MAC). It has beyond-birthday-bound security and is expected to be a possible candidate in constrained environments when instantiated with lightweight blockciphers. Two variants 2kf9 and 1kf9 were proposed to reduce key size for efficiency, but recently, Leurent et al. (CRYPTO\u2718) and Shen et al. (CRYPTO\u2721) pointed out critical flaws on these two variants and invalidated their security proofs with birthday-bound attacks. In this work, we revisit previous constructions of key-reduced variants of 3kf9 and analyze what went wrong in security analyzes. Interestingly, we find that a single doubling at the end can not only fix 2kf9 to go beyond the birthday bound, but also help 1kf9 to go beyond the birthday bound. We then propose two new key-reduced variants of 3kf9, called n2kf9 and n1kf9. By leveraging previous attempts, we prove that n2kf9 is secure up to 2^{2n/3} queries, and prove that n1kf9 is secure up to 2^{2n/3} queries when the message space is prefix-free. We also provide beyond-birthday analysis of n2kf9 in the multi-user setting. Note that compared to EMAC and CBC-MAC, the additional cost to provide a higher security guarantee is expected to be minimal for n2kf9 and n1kf9. It only requires one additional blockcipher call and one doubling

KALwEN: a new practical and interoperable key management scheme for body sensor networks

Key management is the pillar of a security architecture. Body sensor networks (BSNs) pose several challenges–some inherited from wireless sensor networks (WSNs), some unique to themselves–that require a new key management scheme to be tailor-made. The challenge is taken on, and the result is KALwEN, a new parameterized key management scheme that combines the best-suited cryptographic techniques in a seamless framework. KALwEN is user-friendly in the sense that it requires no expert knowledge of a user, and instead only requires a user to follow a simple set of instructions when bootstrapping or extending a network. One of KALwEN's key features is that it allows sensor devices from different manufacturers, which expectedly do not have any pre-shared secret, to establish secure communications with each other. KALwEN is decentralized, such that it does not rely on the availability of a local processing unit (LPU). KALwEN supports secure global broadcast, local broadcast, and local (neighbor-to-neighbor) unicast, while preserving past key secrecy and future key secrecy (FKS). The fact that the cryptographic protocols of KALwEN have been formally verified also makes a convincing case. With both formal verification and experimental evaluation, our results should appeal to theorists and practitioners alike

Towards Tight Security Bounds for OMAC, XCBC and TMAC

OMAC -- a single-keyed variant of CBC-MAC by Iwata and Kurosawa -- is a widely used and standardized (NIST FIPS 800-38B, ISO/IEC 29167-10:2017) message authentication code (MAC) algorithm. The best security bound for OMAC is due to Nandi who proved that OMAC's pseudorandom function (PRF) advantage is upper bounded by O(q^2\ell/2^n), where n, q, and \ell, denote the block size of the underlying block cipher, the number of queries, and the maximum permissible query length (in terms of n-bit blocks), respectively. In contrast, there is no attack with matching lower bound. Indeed, the best known attack on OMAC is the folklore birthday attack achieving a lower bound of \Omega(q^2/2^n). In this work, we close this gap for a large range of message lengths. Specifically, we show that OMAC's PRF security is upper bounded by O(q^2/2^n + q\ell^2/2^n). In practical terms, this means that for a 128-bit block cipher, and message lengths up to 64 Gigabyte, OMAC can process up to 264 messages before rekeying (same as the birthday bound). In comparison, the previous bound only allows 248 messages. As a side-effect of our proof technique, we also derive similar tight security bounds for XCBC (by Black and Rogaway) and TMAC (by Kurosawa and Iwata). As a direct consequence of this work, we have established tight security bounds (in a wide range of \ell) for all the CBC-MAC variants, except for the original CBC-MAC

Proving the TLS Handshake Secure (As It Is)

International audienceThe TLS Internet Standard features a mixed bag of cryptographic algorithms and constructions, letting clients and servers negotiate their use for each run of the handshake. Although many ciphersuites are now well-understood in isolation, their composition remains problematic, and yet it is critical to obtain practical security guarantees for TLS, as all mainstream implementations support multiple related runs of the handshake and share keys between algorithms.We study the provable security of the TLS handshake, as it is implemented and deployed. To capture the details of the standard and its main extensions, we rely on miTLS, a verified reference implementation of the protocol. We propose new agile security definitions and assumptions for the signatures, key encapsulation mechanisms (KEM), and key derivation algorithms used by the TLS handshake. To validate our model of key encapsulation, we prove that both RSA and Diffie-Hellman ciphersuites satisfy our definition for the KEM. In particular, we formalize the use of PKCS#1v1.5 and build a 3,000-line EasyCrypt proof of the security of the resulting KEM against replayable chosen-ciphertext attacks under the assumption that ciphertexts are hard to re-randomize.Based on our new agile definitions, we construct a modular proof of security for the miTLS reference implementation of the handshake, including ciphersuite negotiation, key exchange, renegotiation, and resumption, treated as a detailed 3,600-line executable model. We present our main definitions, constructions, and proofs for an abstract model of the protocol, featuring series of related runs of the handshake with different ciphersuites. We also describe its refinement to account for the whole reference implementation, based on automated verification tools

Performance Considerations for an Embedded Implementation of OMA DRM 2

As digital content services gain importance in the mobile world, Digital Rights Management (DRM) applications will become a key component of mobile terminals. This paper examines the effect dedicated hardware macros for specific cryptographic functions have on the performance of a mobile terminal that supports version 2 of the open standard for Digital Rights Management defined by the Open Mobile Alliance (OMA). Following a general description of the standard, the paper contains a detailed analysis of the cryptographic operations that have to be carried out before protected content can be accessed. The combination of this analysis with data on execution times for specific algorithms realized in hardware and software has made it possible to build a model which has allowed us to assert that hardware acceleration for specific cryptographic algorithms can significantly reduce the impact DRM has on a mobile terminal's processing performance and battery life.Comment: Submitted on behalf of EDAA (http://www.edaa.com/