Efficient Padding Oracle Attacks on Cryptographic Hardware

We show how to exploit the encrypted key import functions of a variety of different cryptographic devices to reveal the imported key. The attacks are padding oracle attacks, where error messages resulting from incorrectly padded plaintexts are used as a side channel. In the asymmetric encryption case, we modify and improve Bleichenbacher’s attack on RSA PKCS#1v1.5 padding, giving new cryptanalysis that allows us to carry out the ‘million message attack’ in a mean of 49 000 and median of 14 500 oracle calls in the case of cracking an unknown valid ciphertext under a 1024 bit key (the original algorithm takes a mean of 215 000 and a median of 163 000 in the same case). We show how implementation details of certain devices admit an attack that requires only 9 400 operations on average (3 800 median). For the symmetric case, we adapt Vaudenay’s CBC attack, which is already highly efficient. We demonstrate the vulnerabilities on a number of commercially available cryptographic devices, including security tokens, smartcards and the Estonian electronic ID card. The attacks are efficient enough to be practical: we give timing details for all the devices found to be vulnerable, showing how our optimisations make a qualitative difference to the practicality of the attack. We give mathematical analysis of the effectiveness of the attacks, extensive empirical results, and a discussion of countermeasures and manufacturer reaction

Evaluation of Cryptography Usage in Android Applications

Mobile application developers are using cryptography in their products to protect sensitive data like passwords, short messages, documents etc. In this paper, we study whether cryptography and related techniques are employed in a proper way, in order to protect these private data. To this end, we downloaded 49 Android applications from the Google Play marketplace and performed static and dynamic analysis in an attempt to detect possible cryptographic misuses. The results showed that 87.8 % of the applications present some kind of misuse, while for the rest of them no cryptography usage was detected during the analysis. Finally, we suggest countermeasures, mainly intended for developers, to alleviate the issues identified by the analysis

A Simple Cast-as-Intended E-Voting Protocol by Using Secure Smart Cards

We propose a simple cast-as-intended remote e-voting protocol where the security is based on the use of secure (and trusted) smart cards that incorporate incard numeric keyboards and LCD displays, and can perform a limited number of cryptographic operations (like encryption, signing, and random number generation). The protocol, while very simple, is significantly more secure (in the sense of ``cast-as-intended\u27\u27) and convenient to use than the e-voting protocol currently used in Norway. The protocol is developed primarily with the idea of deploying it in Estonia within the next $3$ to $10$ years. Since in Estonia, a vast majority of the population already has ID-cards with digital signing and authentication functionality, and the use of ID-cards is a required prerequisite to participate in Estonian e-voting anyway, our assumption of every voter having a secure hardware token makes sense in this concrete context

Analysis of Key Wrapping APIs:Generic Policies, Computational Security

International audienceWe present an analysis of key wrapping APIs with generic policies. We prove that certain minimal conditions on policies are sufficient for keys to be indistinguishable from random in any execution of an API. Our result captures a large class of API policies, including both the hierarchies on keys that are common in the scientific literature and the non-linear dependencies on keys used in PKCS#11. Indeed, we use our result to propose a secure refinement of PKCS#11, assuming that the attributes of keys are transmitted as authenticated associated data when wrapping and that there is an enforced separation between keys used for wrapping and keys used for other cryptographic purposes. We use the Computationally Complete Symbolic Attacker developed by Bana and Comon. This model enables us to obtain computational guarantees using a simple proof with a high degree of modularity

Postcards from the post-HTTP world: Amplification of HTTPS vulnerabilities in the web ecosystem

HTTPS aims at securing communication over the Web by providing a cryptographic protection layer that ensures the confidentiality and integrity of communication and enables client/server authentication. However, HTTPS is based on the SSL/TLS protocol suites that have been shown to be vulnerable to various attacks in the years. This has required fixes and mitigations both in the servers and in the browsers, producing a complicated mixture of protocol versions and implementations in the wild, which makes it unclear which attacks are still effective on the modern Web and what is their import on web application security. In this paper, we present the first systematic quantitative evaluation of web application insecurity due to cryptographic vulnerabilities. We specify attack conditions against TLS using attack trees and we crawl the Alexa Top 10k to assess the import of these issues on page integrity, authentication credentials and web tracking. Our results show that the security of a consistent number of websites is severely harmed by cryptographic weaknesses that, in many cases, are due to external or related-domain hosts. This empirically, yet systematically demonstrates how a relatively limited number of exploitable HTTPS vulnerabilities are amplified by the complexity of the web ecosystem

On the Security of the PKCS#1 v1.5 Signature Scheme

The RSA PKCS#1 v1.5 signature algorithm is the most widely used digital signature scheme in practice. Its two main strengths are its extreme simplicity, which makes it very easy to implement, and that verification of signatures is significantly faster than for DSA or ECDSA. Despite the huge practical importance of RSA PKCS#1 v1.5 signatures, providing formal evidence for their security based on plausible cryptographic hardness assumptions has turned out to be very difficult. Therefore the most recent version of PKCS#1 (RFC 8017) even recommends a replacement the more complex and less efficient scheme RSA-PSS, as it is provably secure and therefore considered more robust. The main obstacle is that RSA PKCS#1 v1.5 signatures use a deterministic padding scheme, which makes standard proof techniques not applicable. We introduce a new technique that enables the first security proof for RSA-PKCS#1 v1.5 signatures. We prove full existential unforgeability against adaptive chosen-message attacks (EUF-CMA) under the standard RSA assumption. Furthermore, we give a tight proof under the Phi-Hiding assumption. These proofs are in the random oracle model and the parameters deviate slightly from the standard use, because we require a larger output length of the hash function. However, we also show how RSA-PKCS#1 v1.5 signatures can be instantiated in practice such that our security proofs apply. In order to draw a more complete picture of the precise security of RSA PKCS#1 v1.5 signatures, we also give security proofs in the standard model, but with respect to weaker attacker models (key-only attacks) and based on known complexity assumptions. The main conclusion of our work is that from a provable security perspective RSA PKCS#1 v1.5 can be safely used, if the output length of the hash function is chosen appropriately

Security Analysis of the W3C Web Cryptography API

International audienceDue to the success of formal modeling of protocols such as TLS, there is a revival of interest in applying formal modeling to standardized APIs. We argue that formal modeling should happen as the standard is being developed (not afterwards) as it can detect complex or even simple attacks that the standardization group may not otherwise detect. As a case example of this, we discuss in detail the W3C Web Cryptography API. We demonstrate how a formal analysis of the API using the modeling language AVISPA with a SAT solver demonstrates that while the API has no errors in basic API operations and maintains its security properties for the most part, there are nonetheless attacks on secret key material due to how key wrapping and usages are implemented. Furthermore, there were a number of basic problems in terms of algorithm selection and a weakness that led to a padding attack. The results of this study led to the removal of algorithms before its completed standardization and the removal of the padding attack via normalization of error codes, although the key wrapping attack is still open. We expect this sort of formal methodology to be applied to new standardization efforts at the W3C such as the W3C Web Authentication API

The 9 Lives of Bleichenbacher\u27s CAT: New Cache ATtacks on TLS Implementations

At CRYPTO’98, Bleichenbacher published his seminal paper which described a padding oracle attack against RSA implementations that follow the PKCS #1 v1.5 standard. Over the last twenty years researchers and implementors had spent a huge amount of effort in developing and deploying numerous mitigation techniques which were supposed to plug all the possible sources of Bleichenbacher-like leakages. However, as we show in this paper most implementations are still vulnerable to several novel types of attack based on leakage from various microarchitectural side channels: Out of nine popular implementations of TLS that we tested, we were able to break the security of seven implementations with practical proof-of-concept attacks. We demonstrate the feasibility of using those Cache-like ATacks (CATs) to perform a downgrade attack against any TLS connection to a vulnerable server, using a BEAST-like Man in the Browser attack. The main difficulty we face is how to perform the thousands of oracle queries required before the browser’s imposed timeout (which is 30 seconds for almost all browsers, with the exception of Firefox which can be tricked into extending this period). The attack seems to be inherently sequential (due to its use of adaptive chosen ciphertext queries), but we describe a new way to parallelize Bleichenbacher-like padding attacks by exploiting any available number of TLS servers that share the same public key certificate. With this improvement, we could demonstrate the feasibility of a downgrade attack which could recover all the 2048 bits of the RSA plaintext (including the premaster secret value, which suffices to establish a secure connection) from five available TLS servers in under 30 seconds. This sequential-to-parallel transformation of such attacks can be of independent interest, speeding up and facilitating other side channel attacks on RSA implementations