Fuzzy Evaluation Scheme for KDF Based on Stream Ciphers

A key derivation function is a function that generate one or more arbitrary length of cryptographic keys from a private string together with some public information. The generated cryptographic key(s) from this key derivation function proposals are generally indistinguishable from random binary strings of the same length based on formal mathematically proof. To date, there are designed of key derivation function proposals using cryptographic primitives such as hash functions, block ciphers and stream ciphers. However, there are limited security analysis of side channel attacks for the key derivation function proposals. This paper is to investigate the timing side channel attacks towards these three types of cryptographic primitives based key derivation function. Key derivation functions based on stream ciphers and block ciphers are input-dependent execution, the experiment results have shown that both key derivation functions proposals are vulnerable against timing side channel.

This paper presents a comprehensive formal security framework for key derivation functions (KDF). The major security goal for a KDF is to produce cryptographic keys from a private seed value where the derived cryptographic keys are indistinguishable from random binary strings. We form a framework of five security models for KDFs. This consists of four security models that we propose: Known Public Inputs Attack (KPM, KPS), Adaptive Chosen Context Information Attack (CCM) and Adaptive Chosen Public Inputs Attack(CPM); and another security model, previously defined by Krawczyk [6], which we refer to as Adaptive Chosen Context Information Attack(CCS). These security models are simulated using an indistinguisibility game. In addition we prove the relationships between these five security models and analyse KDFs using the framework (in the random oracle model).

In this paper, we clarify the security of practical cryptosystems with hash functions based on key derivation functions (KDFs). We use the indifferentiability framework in order to discuss the security because the indifferentiability from Random Oracle (and its variants) guarantees that cryptosystems remain secure even if Random Oracles (ROs) are instantiated with hash functions. Though previous works on the indifferentiability of Merkle-Damgård (MD) hash functions focus on stand-alone hash functions, there is no work which focuses on MD hash functions with KDFs. Many cryptosystems need longer output lengths of hash functions than stand-alone hash functions and KDFs are used to generate longer digests as specified in PKCS #1 v2.1 and IEEE P1363. Specifically, we obtain the following results. We denote the MD hash function using Stam’s type-II compression function by MD-SCFII and MD-SCFII with KDFs by KDF-MD-SCFII. Cryptosystems secure in the pub-RO model (FDH, PSS, Fiat-Shamir, and so on): Dodis et al. proposed the indifferentiability from pub-RO to prove the security of these cryptosystems using MD-SCFII while did not consider the KDF structures. So we propose a different framework, indifferentiability from privleak-RO. Using this framework and their result, we show that these cryptosystems using KDF-MD-SCFIIs are secure. Encryption schemes secure in the RO model (OAEP, RSA-KEM, PSEC-KEM, ECIES-KEM and so on): The encryption schemes are secure in the “fixed inputl length” RO model because the input lengths of ROs from the encryption schemes are fixed. We show that this fact guarantees the security of the encryption schemes using KDF-MD-SCFII. KeywordsHash FunctionEncryption SchemeRandom OracleCompression FunctionRandom Oracle ModelThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Cryptographic Primitives that Resist Backdooring and Subversion

In this article, we first review key derivation functions specified in NIST SP 800-108 and one proposed by Krawczyk. Then, we propose parallelizable key derivation functions obtained by modifying or using the existing schemes. We also define two measures of efficiency of key derivation functions, and evaluate their performance in terms of the two measures.

Farfalle, a permutation-based construction for building a pseudorandom function (PRF), is really versatile. It can be used for message authentication code, stream cipher, key derivation function, authenticated encryption and so on. Farfalle construction relies on a set of permutations and on so-called rolling functions: it can be split into a compression layer followed by a two-step expansion layer.As one instance of Farfalle, Xoofff is very efficient on a wide range of platforms from low-end devices to high-end processors by combining the narrow permutation Xoodoo and the inherent parallelism of Farfalle. In this paper, we present key-recovery attacks on reduced-round Xoofff. After identifying a weakness in the expanding rolling function, we first propose practical attacks on Xoofff instantiated with 1-/2-round Xoodoo in the expansion layer. We next extend such attack on Xoofff instantiated with 3-/4-round Xoodoo in the expansion layer by making use of Meet-in-the-Middle algebraic attacks and the linearization technique. All attacks proposed here – which are independent of the details of the compression and/or middle layer – have been practically verified (either on the “real” Xoofff or on a toy-version Xoofff with block-size of 96 bits). As a countermeasure, we discuss how to slightly modified the rolling function for free to reduce the number of attackable rounds.KeywordsFarfalleXoofffXoodooKey-recovery attacks

Key derivation functions are commonly used within many cryptographic schemes in order to distribute the entropy contained in an uneven way in a long stream of bits into a string that can be used directly as a symmetric key or as a seed for a pseudo-random number generator, or to convert short strings such as passwords into symmetric keys. This paper examines the common key derivation function constructions and shows that most of these have some concerning properties. In some situations, the use of these key derivation functions may actually limit the security that would otherwise be obtained. A new construction is also provided which seems to have better properties and an intuitive justification for its security is given.

Recent lightweight hardware-based stream cipher designs keep an external non-volatile internal state that is not part of the cipher’s hardware module. The purpose of these so-called small-state ciphers is to keep the size of the hardware and the power consumption low. We propose a random oracle model for stream ciphers. This will allow us to analyse the recent small-state stream cipher designs’ resistance against generic attacks and, in particular, time-memory-data tradeoff attacks. We analyse the conventional construction underlying stream ciphers like Grain and Trivium, constructions continuously using the external non-volatile secret key during keystream generation like Sprout, Plantlet, Fruit, and Atom, constructions continuously using the external non-volatile IV, and constructions using a combination of the IV and the key like DRACO. We show the tightness of all bounds by first presenting the time-memory-data tradeoff attacks on the respective constructions, establishing the upper bound on security, and then presenting the proof of security to establish the lower bound on security. In this work, we extend the theoretical work done by Hamann et al. who introduced the DRACO stream cipher at FSE 2023. We use the same random oracle model as the aforementioned work and apply it to the earlier work by Hamann et al. presented at SAC 2019, which showed security for two of the four constructions we consider in this work. Our model is equivalent but allows for a much simpler proof of security. Furthermore, we provide a proof of security for stream ciphers continuously using the secret key during keystream generation, giving upper and lower bounds for all four generic stream cipher constructions proposed so far.

Authentication is a ubiquitous task in users' daily lives. The dominant form of user authentication are text passwords. They protect private accounts like online banking, gaming, and email, but also assets in organisations. Yet, many issues are associated with text passwords, leading to challenges faced by both, users and organisations. This thesis contributes to the body of research enabling secure and usable user authentication, benefiting both, users and organisations. To that end, it addresses three distinct challenges. The first challenge addressed in this thesis is the creation of correct, complete, understandable, and effective password security awareness materials. To this end, a systematic process for the creation of awareness materials was developed and applied to create a password security awareness material. This process comprises four steps. First, relevant content for an initial version is aggregated (i.e. descriptions of attacks on passwords and user accounts, descriptions of defences to these attacks, and common misconceptions about password and user account security). Then, feedback from information security experts is gathered to ensure the correctness and completeness of the awareness material. Thereafter, feedback from lay-users is gathered to ensure the understandability of the awareness material. Finally, a formal evaluation of the awareness material is conducted to ensure its effectiveness (i.e. whether the material improves participant's ability to assess the security of passwords as well as password-related behaviour and decreases the prevalence of common misconceptions about password and user account security). The results of the evaluation show the effectiveness of the awareness material: it significantly improved the participants' ability to assess the security of password-related behaviour as well as passwords and significantly decreased the prevalence of misconceptions about password and user account security. The second challenge addressed in this thesis is shoulder-surfing resistant text password entry with gamepads (as an example of very constrained input devices) in shared spaces. To this end, the very first investigation of text password entry with gamepads is conducted. First, the requirements of authentication in the gamepad context are described. Then, these requirements are applied to assess schemes already deployed in the gamepad context and shoulder-surfing resistant authentication schemes from the literature proposed for non-gamepad contexts. The results of this assessment show that none of the currently deployed and only four of the proposals in the literature fulfil all requirements. Furthermore, the results of the assessment also indicate a need for an empirical evaluation in order to exactly gauge the shoulder-surfing threat in the gamepad context and compare alternatives to the incumbent on-screen keyboard. Based on these results, two user studies (one online study and one lab study) are conducted to investigate the shoulder-surfing resistance and usability of three authentication schemes in the gamepad context: the on-screen keyboard (as de-facto standard in this context), the grid-based scheme (an existing proposal from the literature identified as the most viable candidate adaptable to the gamepad context during the assessment), and Colorwheels (a novel shoulder-surfing resistant authentication scheme specifically designed for the gamepad context). The results of these two user studies show that on-screen keyboards are highly susceptible to opportunistic shoulder-surfing, but also show the most favourable usability properties among the three schemes. Colorwheels offers the most robust shoulder-surfing resistance and scores highest with respect to participants' intention to use it in the future, while showing more favourable usability results than the grid-based scheme. The third challenge addressed in this thesis is secure and efficient storage of passwords in portfolio authentication schemes. Portfolio authentication is used to counter capture attacks such as shoulder-surfing or eavesdropping on network traffic. While usability studies of portfolio authentication schemes showed promising results, a verification scheme which allows secure and efficient storage of the portfolio authentication secret had been missing until now. To remedy this problem, the (t,n)-threshold verification scheme is proposed. It is based on secret sharing and key derivation functions. The security as well as the efficiency properties of two variants of the scheme (one based on Blakley secret sharing and one based on Shamir secret sharing) are evaluated against each other and against a naive approach. These evaluations show that the two (t,n)-threshold verification scheme variants always exhibit more favourable properties than the naive approach and that when deciding between the two variants, the exact application scenario must be considered. Three use cases illustrate as exemplary application scenarios the versatility of the proposed (t,n)-threshold verification scheme. By addressing the aforementioned three distinct challenges, this thesis demonstrates the breadth of the field of usable and secure user authentication ranging from awareness materials, to the assessment and evaluation of authentication schemes, to applying cryptography to craft secure password storage solutions. The research processes, results, and insights described in this thesis represent important and meaningful contributions to the state of the art in the research on usable and secure user authentication, offering benefits for users, organisations, and researchers alike.

Password-based key derivation functions are of particular interest in cryptography because they (a) input a password/passphrase (which usually is short and lacks enough entropy) and derive a cryptographic key; (b) slow down brute force and dictionary attacks as much as possible. In PKCS#5 [17], RSA Laboratories described a password based key derivation function called PBKDF2 that has been widely adopted in many security related applications [6, 7, 11]. In order to slow down brute force attacks, PBKDF2 introduce CPU-intensive operations based on an iterated pseudorandom function. Such a pseudorandom function is HMAC-SHA-1 by default. In this paper we show that, if HMAC-SHA-1 is computed in a standard mode without following the performance improvements described in the implementation note of RFC 2104 [13] and FIPS 198-1 [14], an attacker is able to avoid 50 % of PBKDF2’s CPU intensive operations, by replacing them with precomputed values. We note that a number of well-known and widely-used crypto libraries are subject to this vulnerability.In addition to such a vulnerability, we describe some other minor optimizations that an attacker can exploit to reduce even more the key derivation time.

Cumulative memory—the sum of space used per step over the duration of a computation—is a fine-grained measure of time-space complexity that was introduced to analyze cryptographic applications like password hashing. It is a more accurate cost measure for algorithms that have infrequent spikes in memory usage and are run in environments such as cloud computing that allow dynamic allocation and de-allocation of resources during execution, or when many instances of an algorithm are interleaved in parallel. We prove the first lower bounds on cumulative memory complexity for both sequential classical computation and quantum circuits. Moreover, we develop general paradigms for bounding cumulative memory complexity inspired by the standard paradigms for proving time-space tradeoff lower bounds that can only lower bound the maximum space used during an execution. The resulting lower bounds on cumulative memory that we obtain are just as strong as the best time-space tradeoff lower bounds, which are very often known to be tight. Although previous results for pebbling and random oracle models have yielded time-space tradeoff lower bounds larger than the cumulative memory complexity, our results show that in general computational models such separations cannot follow from known lower bound techniques and are not true for many functions. Among many possible applications of our general methods, we show that any classical sorting algorithm with success probability at least 1/poly( n ) requires cumulative memory \(\tilde{\Omega }(n^2) \) , any classical matrix multiplication algorithm requires cumulative memory Ω ( n 6 / T ), any quantum sorting circuit requires cumulative memory Ω ( n 3 / T ), and any quantum circuit that finds k disjoint collisions in a random function requires cumulative memory Ω ( k 3 n / T 2 ).

This work introduces an innovative method for image steganography that merges cryptographic and steganographic techniques to meet the increasing demand for the secure sharing of sensitive data. The suggested approach utilizes a combination of Hybrid Beaufort Vigenere (HBV) Cipher and padded RSA algorithm for encryption, and an improved LSB steganography method to render the embedded data invisible to potential attackers. To further enhance key sensitivity, a key derivation function is integrated.The effectiveness of the algorithm is evaluated through multiple metrics, including peak signal-to-noise ratio (PSNR), structural similarity index measure (SSIM), mean squared error (MSE), correlation coefficient (CC) score, histogram analysis, processing time and key sensitivity. The findings indicate that the suggested method outperforms existing techniques in all examined parameters. However, it should be noted that although the research focuses on image steganography security using the proposed method, it may not be directly applicable to other steganographic techniques or media. Implementing the proposed method in secure communication systems that require sharing sensitive data can effectively ensure the confidentiality and integrity of transmitted information. The novelty of this paper stems from the integration of cryptographic and steganographic methods, providing enhanced security and resistance to various types of attacks through the combination of HBV, padded RSA, and an improved LSB steganography method. Additionally, the integration of a key derivation function further strengthens the technique’s key sensitivity.

In the first article of a series on building software as a service (SaaS) applications with security in mind, the author discusses best practices for user authentication, including cloud-based authentication services, key derivation functions, and two-factor authentication options.

The EAP-GPSK protocol is a lightweight, flexible authentication protocol relying on symmetric key cryptography. It is part of an ongoing IETF process to develop authentication methods for the EAP framework. We analyze the protocol and find three weaknesses: a repairable Denial-of-Service attack, an anomaly with the key derivation function used to create a short-term master session key, and a ciphersuite downgrading attack. We propose fixes to these anomalies, and use a finite-state verification tool to search for remaining problems after making these repairs. We then prove the fixed version correct using a protocol verification logic. We discussed the attacks and our suggested fixes with the authors of the specification document which has subsequently been modified to include our proposed changes.

In FDTC 2009, Li et al. published a DFA attack [20] against the symmetric block cipher SHACAL1 [11]. This block cipher substantially consists of the compression function of the hash function SHA1 [16] except for the final addition operation. When using the SHA1 compression function as a primitive in a keyed hash function like HMAC-SHA1 [17] or in a key derivation function it might be of some interest if the attack of Li et al. also applies to the SHA1 compression function. However, the final addition operation turns out to completely prevent this direct application. In this paper we extend the attack of Li et al. in order to overcome the problem of the final addition and to extract the secret inputs of the SHA1 compression function by analysing faulty outputs. Our implementation of the new attack needs about 1000 faulty outputs and a computation time of three hours on a normal PC to fully extract the secret inputs with high probability.