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Blind image watermarking is regarded as a vital technology to provide copyright of digital images. Due to the rapid growth of deep neural networks, deep learning-based watermarking methods have been widely studied. However, most existing methods which adopt simple embedding and extraction structures cannot fully utilize the image features. In this paper, we propose a novel Single-Encoder-Dual-Decoder (SEDD) watermarking architecture to achieve high imperceptibility and strong robustness. Precisely, the single encoder utilizes normalizing flow to realize watermark embedding, which can effectively fuse the watermark and cover image. For watermark extraction, we introduce a parallel dual-decoder to improve the imperceptibility and extracting ability. Extensive experiments demonstrate that better watermark robustness and imperceptibility are obtained by SEDD architecture. Our method achieves a bit error rate less than 0.1% under most attacks such as JPEG compression, Gaussian blur and crop. Besides, the proposed method also obtains strong robustness under combined attacks and social platform processing. [ABSTRACT FROM AUTHOR]

Cryptographic systems refer to a set of algorithms needed to implement a particular form of encryption, decryption, signature and verification, which have practical applications in engineering area. Among cryptographic systems, Multivariate Public Key Cryptography (MPKC) is one of the most popular post-quantum candidates since it has the potential to resist quantum computer attacks. MPKC must be protected against a wide range of attacks, including side-channel attack, which is any attack based on information gained from the physical implementation of cryptographic systems. However, there are few side-channel attacks on MPKC schemes. In this paper, we present techniques to exploit Differential Power Analysis and fault analysis attacks for analyzing the effectiveness of side-channel attacks on MPKC schemes. We propose a general model of side-channel attacks on enhanced Tame Transformation Signature (enTTS) scheme, which is one of the representative MPKC schemes. We implement a naive enTTS scheme on Application Specific Integrated Circuits and propose a successful side-channel attack on the implementation. Experimental results show that our attack successfully obtains all the pieces from the private keys of the enTTS scheme and they clearly demonstrate the importance of protecting MPKC against side-channel attacks. [ABSTRACT FROM AUTHOR]

Anonymous multi-receiver identity-based encryption can protect the receiver identity privacy and message confidentiality. Thus, it can be used in many fields, such as Voice over Internet Protocol and pay-TV systems. In 2012, Chien improved an anonymous multi-receiver identity-based encryption scheme. This paper points out that Chien's scheme does not satisfy the indistinguishability of encryptions under selective multi-identity, chosen ciphertext attacks. The analysis is important for understanding the security risks. [ABSTRACT FROM AUTHOR]

Identity-based encryption (IBE) has many appealing applications. However, some traditional IBE schemes may not be secure in the real world due to the side-channel attacks. Leakage-resilient cryptography can capture these attacks by modeling information leakage that adversary can access. In this paper, we apply a hash proof technique in the existing CCA-secure variant of the Gentry's IBE scheme to construct a new leakage-resilient IBE scheme in the bounded-leakage model. The proposed scheme is more computationally efficient than the original Alwen et al.'s leakage-resilient IBE scheme. It enjoys a shorter key (public/secret key) length, and a higher relative key leakage ratio. The new leakage-resilient scheme is proved semantically secure against adaptive chosen ciphertext attack in the standard model under the truncated augmented bilinear Diffie-Hellman exponent (q-TABDHE) assumption. [ABSTRACT FROM AUTHOR]

With the purpose of taking physical attacks into account in security proofs, leakage-resilient cryptography has been initiated. Recently, many leakage-resilient cryptographic primitives have been proposed. In this paper, we put forward the first leakage-resilient wicked identity-based encryption (wicked IBE) scheme. To achieve this goal, we first present a new wicked IBE scheme in the composite order groups. The security proof of this scheme is achieved via the dual system encryption technique. In contrast with existing wicked IBE schemes, the new proposal can be proved fully secure in the standard model, even when the maximum hierarchy depth is a polynomial in the security parameter. Moreover, its security is based on some standard assumptions in the composite groups, which are independent of the hierarchy depth of the scheme. Based on this newly proposed scheme, we then put forward a fully secure leakage-resilient wicked IBE scheme in the bounded memory-leakage model. The leakage here is not only allowed on the user's secret key, but also on the master secret key. Its security is proved in the standard model by a hybrid argument in a sequence of computationally indistinguishable games. To the best of our knowledge, this is the first wicked IBE scheme in the context of leakage resilience. [ABSTRACT FROM AUTHOR]

In this paper, we present a methodology to evaluate the feasibility, effectiveness and complexity of a class of cache-based side-channel attacks. The methodology provides estimates on the lower bound of the required number of observations on the side channel and the number of trials for a successful attack. As a case study, a weak implementation of the Advanced Encryption Standard algorithm is selected to apply the proposed methodology to three different categories of cachebased attacks; namely, access-driven, trace-driven and time-driven attacks. The approach, however, is generic in the sense that it can be utilized in other algorithms that are subject to the microarchitectural side-channel attacks. The adopted approach bases its analysis method partially on the conditional entropy of secret keys given the observations of the intermediate variables in software implementations of cryptographic algorithms via the side channel and explores the extent to which the observations can be exploited in a successful attack. Provided that the intermediate variables are relatively simple functions of the key material and the known inputs or outputs of cryptographic algorithms, a successful attack is theoretically feasible. Our methodology emphasizes the need for an analysis of this leakage through such intermediate variables and demonstrates a systematic way to measure it. The method allows us to explore every attack possibility, estimate the feasibility of an attack, and compare the efficiency and the costs of different attack strategies to determine an optimal level of effective countermeasures. [ABSTRACT FROM AUTHOR]

In Cramer et al. (2007, Bounded CCA2-Secure Encryption. In Kurosawa, K. (ed.), Advances in Cryptology - ASIACRYPT 2007, Kuching, Malaysia, December 2-6, Lecture Notes in Computer Science, Vol. 4833, pp. 502-518. Springer, Berlin, Germany) proposed a public-key encryption scheme secure against adversaries with a bounded number of decryption queries based on the decisional Diffie-Hellman problem. In this paper, we show that the same result can be obtained based on weaker computational assumptions, namely: the computational Diffie-Hellman and the hashed Diffie-Hellman assumptions. [ABSTRACT FROM AUTHOR]

Certificateless encryption (CLE) can be used to prevent the key generation centre from decrypting ciphertexts (which addresses the key escrow problem of identity-based encryption), but it cannot provide user revocation mechanism by default. A revocable CLE scheme was proposed by Shen et al. (2014. Efficient revocable certificateless encryption secure in the standard model. Comput. J., 57, 592-601) which realizes the revocation by requiring a time key in the decryption process. Despite of their security proofs, this paper shows an attack of their revocation mechanism. [ABSTRACT FROM AUTHOR]

The well-known Welch-Gong (WG) stream cipher, proposed by Nawaz and Gong in 2005, was submitted to the hardware profile of the eSTREAM project. In the last several years, the original WGhas come under several cryptanalytic attacks. However, as for the final version ofWG, no attack has been published on it until now. In this paper, an efficient key recovery attack on the final WG stream cipher in the related key setting is proposed. Under related keys, we can recover the 128-bit secret key of WG-128 with a time complexity of 289 and a memory complexity of 245. The success probability of the attack is 0.6321. This result shows that our attack on WG-128 is much better than an exhaustive key search in the related key setting. Furthermore, our cryptanalytic results show that WG with IV size no less than 80 bits is vulnerable to a related key attack. The main feature of our attack is that it is independent of the number of steps in the key/IV setup ofWG, and then increasing the number of steps in the key/IV setup cannot strengthen the resistance of WG against a related key attack. Finally, a recommended approach to repair the weakness and strengthen the resistance of WG against a related key attack is presented. [ABSTRACT FROM AUTHOR]

Recently, Gu et al. proposed an efficient identity-based proxy signature scheme and demonstrated their scheme was provably secure in the standard model. In this paper, we show their scheme is not secure against the malicious user through proposing three concrete attacks. [ABSTRACT FROM AUTHOR]

Related-key attacks (RKAs) are a flavor of powerful physical attacks, which allow an adversary to modify the secret key stored in a cryptographic device and subsequently observe the effect of such modifications on the output of the device. Designing secure encryption schemes against such attacks is a challenging task, especially for a large class of such physical attacks which are usually captured by related-key derivation functions. In this work, we achieve the security of public key encryptions (PKEs) against a new and broad function class that consists of almost all efficiently invertible functions in two different ways. Specifically, we first give a generic construction of PKE which is proven secure against such a broad function class under the standard chosen-ciphertext security. Moreover, we present two practical concrete constructions, both of which are shown to be secure against such function class under standard assumptions in the standard model. At last, we give a detailed performance analysis, which shows that our constructions can not only resist to a large class of RKAs but also achieve a good efficiency. [ABSTRACT FROM AUTHOR]

Recent research shows that many public-key or identity-based encryption schemes are vulnerable to side-channel attacks on the keys by the interaction of an adversary with a physical device. To tolerate the possible key leakage, leakage-resilient cryptography models a class of leakage output by allowing the adversary to be able to specify a computable leakage function and obtaining the partial keys or other possibly internal states from the output of function. In this article, we propose a leakage-resilient hidden-vector encryption (HVE) scheme that supports the predicate operators such as conjunction, disjunction, comparison, range query and subset query, etc. The proposed scheme is leakage-resilient attribute-hiding secure in the sense that the adversary cannot only obtain the tokens of non-match vectors but also learn amount of key information of the vector that matches the challenge vector. To the best of our knowledge, this is the first HVE that supports token-leakage resilience. We prove the security with a series of computationally indistinguishable games that uses the dual system encryption mechanism. We also analyze and discuss the performance of leakage bound parameters and leakage fraction in the practical security level. Finally, we also give an extensive scheme to achieve the security of both attribute-hiding and payload-hiding, and analyze the performance in larger alphabets. [ABSTRACT FROM PUBLISHER]

We put forward a notion of forward security for stateful public-key encryption against state exposure and chosen ciphertext attack. This new notion is important in mobile applications in which small devices that perform ‘stateful encryptions’ are vulnerable to attacks which can result in the compromise of internal states. We precisely formulate a security definition and propose two efficient schemes which are provably secure under standard computational assumptions. [ABSTRACT FROM PUBLISHER]