Cryptographic Primitives that Resist Backdooring and Subversion

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.

At CRYPTO 2014 Bellare, Paterson, and Rogaway (BPR) presented a formal treatment of symmetric encryption in the light of algorithm substitution attacks (ASAs), which may be employed by ‘big brother’ entities for the scope of mass surveillance. Roughly speaking, in ASAs big brother may bias ciphertexts to establish a covert channel to leak vital cryptographic information. In this work, we identify a seemingly benign assumption implicit in BPR’s treatment and argue that it artificially (and severely) limits big brother’s capabilities. We then demonstrate the critical role that this assumption plays by showing that even a slight weakening of it renders the security notion completely unsatisfiable by any, possibly deterministic and/or stateful, symmetric encryption scheme. We propose a refined security model to address this shortcoming, and use it to restore the positive result of BPR, but caution that this defense does not stop most other forms of covert-channel attacks.

The main topic of this thesis is related to the state of the art in designing cryptographic primitives from a hardware point of view. A special emphasis is dedicated to low-power/low-energy CMOS design. A set of solutions is proposed including an LFSR based stream cipher with self-synchronizing capabilities, a new memory-less Rijndael block cipher architecture and a public key scheme in the class of discrete logarithm. The former is based on arithmetic in large finite field, mainly Galois extension field GF(2‴). These solutions are droved using low-energy techniques, in order to decrease both the switching activity and the total delay. The fundamental motivation supporting this work, is to demonstrate that practical solutions can be obtained for implementing such complex primitives in large scaled circuits, that arc at once, high performance architectures (low-power, high-speed) and cryptographicaly strong, using the well known trade-off between area-speed or area-power. Security constraint has been duly considered, mainly by increasing the key-size. In this work, we explore the general aspects of designing the above mentioned cryptographic functions. We give an extensive survey of some cryptographic primitives from the hardware point of view and expose their security properties. The thesis favours stream cipher and public-key schemes, as currently the most promising advance to capture the notion of key generation and establishment and data bulk encryption. One contribution is the convenient notation for expressing cryptographic self-synchronizing stream ciphers SSSC schemes and our SSMG proposal, a scheme based on packet fingerprint identification, that relies on keyed cryptographic hash function to achieve the security requirements. We maintain an important distinction between hardware implementation and algorithm's security, because the security of cryptographic primitives cannot be based on mathematically strong functions only but requires an extensive cryptanalysis at different levels including the application. This causes a concern for a formalization of the security of an implemented cryptographic primitive. Nevertheless, while some schemes arc well known to be secure such as DL based public key schemes and enough cryptanalyzed such as the new standard Rijndael, some security aspects of the SSMG are discussed. A part of this work studies the specific aspects related to hardware implementation of Rijndael block cipher, the new standard designed to be a substitute for DES. An efficient architecture is developed targeting FPGA implementation, by simply avoiding memory blocks dedicated to the implementation of S-boxes and replacing them by on-chip forward computation using composite Galois field. This technique helps to reduce considerably the amount of hardware required at the cost of little increase of the switching activity. The main conclusion is that, while security constraint of cryptographic primitives increases the hardware complexity and reduces the performances, practical solutions exist for reducing such complexities while keeping or increasing the level of security. Nevertheless, major open questions remain both for a firm theoretical foundation and the proper cryptanalysis of certain solutions.

This paper analyzes the computer security of systems and importance of the digital signature and hashing message algorithm. The proposed digital signature algorithm gives a new technology for producing effective output of digital signature as a result the signing 1 and verifying of signatures are very fast compared to earlier ones. To improve the security and authentication of sending data, this method uses "Message Digest", "IDEA" and "GOST" 2 algorithms. The new message digest algorithm is to provide high security, to transfer data by combination of digital signature algorithm and symmetric key cryptography algorithm. The new hashing algorithm proposed creates a unique digital fingerprint along with symmetric key encryption generated IDEA and GOST algorithms 3,4 . The receiver used the symmetric key and hashing algorithm to form a signature. If this message digest match with the sender digests the message the content will be decrypted and read by sender.

We construct a publicly verifiable protocol for proving computational work based on collision-resistant hash functions and a new plausible complexity assumption regarding the existence of hash functions. Our protocol is based on a novel construction of puzzles. Given a sampled P getsr Dn, where $n$ is the security parameter and Dn is the distribution of the puzzles, a corresponding can be generated using N evaluations of the sequential hash function, where N>n is another parameter, while any feasible adversarial strategy for generating valid solutions must take at least as much time as Ω(N) serial evaluations of the hash function after receiving $P$. Thus, valid solutions constitute a proof that Ω(N) parallel time elapsed since p was received. Solutions can be publicly and efficiently verified in time poly(n) ⋅ polylog(N). Applications of these time-lock include noninteractive timestamping of documents (where the distribution over the possible documents corresponds to the puzzle distribution Dn) and universally verifiable CPU benchmarks. Our construction is secure in the standard model under complexity assumptions (collision-resistant hash functions and inherently sequential hash functions), and makes black-box use of the underlying primitives. Consequently, the corresponding construction in the random oracle model is secure unconditionally. Moreover, as it is a public-coin protocol, it can be made non-interactive in the random oracle model using the Fiat-Shamir Heuristic.Our construction makes a novel use of depth-robust directed acyclic graphs---ones whose depth remains large even after removing a constant fraction of vertices---which were previously studied for the purpose of complexity lower-bounds. The construction bypasses a recent lower-bound of Mahmoody, Moran, and Vadhan (CRYPTO '11) for puzzles in the random oracle model, which showed that it is impossible to have puzzles like ours in the random oracle model if the puzzle generator also computes a solution together with the puzzle.

Cryptographic hash functions are efficiently computable functions that shrink a long input into a shorter output while achieving some of the useful security properties of a random function. The most common type of such hash functions is collision resistant hash functions (CRH), which prevent an efficient attacker from finding a pair of inputs on which the function has the same output.

A cryptographic scheme is “provably secure” if an attack on the scheme implies an attack on the underlying primitives it employs. A cryptographic scheme is “provably secure in the random-oracle model” if it uses a cryptographic hash function F and is provably secure when F is modeled by a public random function. Demonstrating that a crypto graphic scheme is provably secure in the random-oracle model engenders much assurance in the scheme's correctness. But there may remain some lingering fear that the concrete hash function which instantiates the random oracle differs from a random function in some significant way. So it is good to limit reliance on random oracles. Here we describe two encryption schemes which use their random oracles in a rather limited way. The schemes achieve semantic security and plaintext awareness under specified assumptions. One scheme uses the RSA primitive; another uses Diffie-Hellman. In either case messages longer than the modulus length can be safely and directly encrypted without relying on the hash functions modeled as random-oracles to be good for private-key encryption.

Confidentiality and authenticity are two fundamental security requirement of Public key Cryptography. These are achieved by encryption scheme and digital signatures respectively. Wireless sensor networks are commonly used for critical security tasks such as intrusion or tamper detection, and therefore must be protected. The article proposes a provable secure signcryption scheme in Random oracle model for wireless security. It enables nodes to authenticate each other by keeping the information confidential. Also achieve data integrity in the communication. Security of the scheme is based on q-Diffie Hellman Problem. We modify the scheme proposed by Libert et al. and proposed a provably secure scheme with respect to security under assumptions of Strong Diffie-Hellman (SDH) and Diffie-Hellman Inversion (DHI) in the random oracles.

In this paper, the existence of multicollisions in Zipper Hash structure, a new Hash structure which was introduced to strengthen the iterated Hash structures, is presented. This study shows that finding multicollisions, i.e. 2k-way collision, in this Hash structure is not much harder than finding such multicollisions in ordinary Merkle - Damgard (MD) structure. In fact, the complexity of the attacks is approximately n/2 times harder than what has been found for MD structures. Then, these large multicollisions are used as a tool to find D-way preimage for this structure. The complexity of finding 2K-way multicollisions and 2k-way preimages are (eq) and (eq) respectively. Similar to what has been proved by Joux for MD, it is shown in this paper that this structure could not be used to create a Hash function with 2n-bit length by concatenating this structure with any other Hash structure by Hash’s output length of n-bite. It is also shown that time complexity of finding a collision for this concatenated structure is (eq) which is much smaller than what was expected from generic-birthday attack which would be (eq) . In addition, it is shown that increasing the number of rounds of this Hash function can not improve its security against this attack significantly and the attacker can find multicollisions on this Hash function which means that this Hash function has a structural flaw.

Hash functions, which can extract message digest from input messages as output, play an important role in digital signature and authentication. Meanwhile, Hash functions are essential in many cryptographic protocols and regimes. With the research becoming more and more in depth, a series of Hash functions is proposed, such as MD series and SHA series. At the same time, the security analysis and attacks against Hash functions are carried out. The security of Hash functions is threatened. In this case, how to improve the security of the Hash functions becomes the primary concern. In this paper, an optical Hash function based on the interaction between light and multiple scattering media is proposed. Unlike most of the traditional Hash functions which are based on mathematical transformations or complex logic operations, this method innovatively takes advantage of the natural random scattering effect of multiple scattering media on coherently modulated light, and realizes the “confusion” and “diffusion” of modulated light, which satisfies the core functional requirement of the Hash function: one-way encoding/encryption with strong security. The photoelectric hybrid system designed by this method can effectively simulate the "compression function" in the Hash function. Combined with the Sobel filter with feature extraction function, the input data of arbitrary length can be compressed and encrypted into the output with a fixed length of 256-bit (Hash value). The principle of the proposed optical Hash function can be described as follows. 1) Two 8-bit images with a size of 16×16 pixels are loaded in SLM<sub>1</sub> (amplitude-only spatial modulator) and SLM<sub>2</sub> (phase-only spatial modulator) respectively. 2) The coherent wavefront is modulated by SLM<sub>1</sub> and SLM<sub>2</sub>, and then propagates on multiple scattering media. 3) A speckle pattern is recorded by CCD because of the confusion of multiple scattering media. 4) The features of the speckle pattern, which is extracted by Sobel filter, serve as the input of the next compression function. For the unpredicted and non-duplicated disorder multiple scattering media, it is tremendously difficult to determine the internal state of the multiple scattering media. Therefore, the proposed optical Hash function is considered to have a high security. A series of simulation results shows that the proposed optical Hash function has a good “avalanche effect” and “collision resistance”, and its security performance is comparable to that of the most widely used traditional Hash functions (MD5 and SHA-1).

SummaryObjects/tags are generally passes through multiple readers before achieving the final destination within the IoT network. Hence, object identification is a significant issue as some bogus objects may take part for malicious access. Considering this situation, RFID can be used for unique identification and validation of IoT objects. However, it recognizes many objects at the same time and faces limitations like non‐repudiations, injection of fake objects, and unclonability issues. Alternatively, security limitations between tags and readers are analyzed and found that whole communication depends on limited computational resource and simple operations such as hash function, XOR operation, and so forth. Moreover, the communication channel between reader and backend server is secure due to symmetric or asymmetric key encryption algorithms. As the information is exchanged by the tags with readers, a secure path must be maintained among them for safe communication with cloud server. For the development of secure path and verification of objects, ECC‐based Cramer‐Shoup encryption, cryptographic authentication protocol (CAP), and device fingerprinting can be used. To overcome the existing limitations, we are motivated to design an ECC‐based secure object tracking and key exchange protocol that allows the owner device to be offline during communication. This suggested scheme is referred as ESOTP. Several recognized cryptographic attacks are evaluated, the security strength is validated and found that ESOTP is resilient against those attacks. Finally, a comparative study is performed regarding the security features and performance efficiency of ESOTP with other existing schemes and enhanced results are found.

We study entropy flattening: Given a circuit CX implicitly describing an n-bit source X (namely, X is the output of CX on a uniform random input), construct another circuit CY describing a source Y such that (1) source Y is nearly flat (uniform on its support), and (2) the Shannon entropy of Y is monotonically related to that of X. The standard solution is to have CY evaluate CX altogether Θ(n2) times on independent inputs and concatenate the results (correctness follows from the asymptotic equipartition property). In this paper, we show that this is optimal among black-box constructions: Any circuit CY for entropy flattening that repeatedly queries CX as an oracle requires ω(n2) queries.Entropy flattening is a component used in the constructions of pseudorandom generators and other cryptographic primitives from one-way functions [12, 22, 13, 6, 11, 10, 7, 24]. It is also used in reductions between problems complete for statistical zero-knowledge [19, 23, 4, 25]. The Θ(n2) query complexity is often the main efficiency bottleneck. Our lower bound can be viewed as a step towards proving that the current best construction of pseudorandom generator from arbitrary one-way functions by Vadhan and Zheng (STOC 2012) has optimal efficiency.

The algorithms in this chapter are very different from those in the previous chapter (symmetric key encryption). A Hash Function is a one-way process (there is no way to recover the original information from a message digest). There is no key (a given plaintext will always produce exactly the same message digest). With symmetric key cryptography, the output is roughly the same size as the input. With a hash function, the output is always a fixed length (based on the algorithm used, e.g. 256 bits for SHA2-256). Hash functions are used in very different ways than encryption algorithms.

Enhanced Target Collision Resistance (eTCR) property for a hash function was put forth by Halevi and Krawczyk in Crypto 2006, in conjunction with the randomized hashing mode that is used to realize such a hash function family. eTCR is a strengthened variant of the well-known TCR (or UOWHF) property for a hash function family (i.e. a dedicated-key hash function). The contributions of this paper are twofold. First, we compare the new eTCR property with the well-known collision resistance (CR) property, where both properties are considered for a dedicated-key hash function. We show there is a separation between the two notions, that is in general, eTCR property cannot be claimed to be weaker (or stronger) than CR property for any arbitrary dedicated-key hash function. Second, we consider the problem of eTCR property preserving domain extension. We study several domain extension methods for this purpose, including (Plain, Strengthened, and Prefix-free) Merkle-Damgard, Randomized Hashing (considered in dedicated-key hash setting), Shoup, Enveloped Shoup, XOR Linear Hash (XLH), and Linear Hash (LH) methods. Interestingly, we show that the only eTCR preserving method is a nested variant of LH which has a drawback of having high key expansion factor. Therefore, it is interesting to design a new and efficient eTCR preserving domain extension in the standard model.

The field of network security has evolved significantly over the years, with new threats emerging and security measures adapting in response. Network security problems exist through all the layers of the computer network, and the network security objective is to maintain the confidentiality, authenticity, integrity, dependability, availability, and suitability of the network. The rapid development of computer network systems brings both great convenience and new security threats for users. Network security problems generally include network system security and data security. Specifically, it refers to the reliability of the network system, confidentiality, integrity, and availability of data information in the system. This paper aims to trace the timeline of network security in chronological order, starting from the early days of computing to the present day. The paper will explore the major milestones in the development of network security, including the emergence of viruses, the introduction of firewalls, and the rise of cybercrime. By examining the historical context of these developments, this paper will provide a deeper understanding of the evolution of network security and the challenges that continue to shape the field today. Ultimately, this paper will demonstrate how network security has become an essential component of modern computing, and how its evolution has helped shape the digital world we live in today. Index Terms — Access Control, Anti-Virus, Asymmetric Key, Authentication, Availability, Cipher, Clearance levels, Confidentiality, Data encryption, DevSecOps, Firewalls, Firmware, Hash Function, IDS, Integrity, Intrusion, NAT, Security, Security Audits, SOAR, Symmetric Key, VPN, XDR