Design of Rabin-like cryptosystem without decryption failure

In this work, we design a new, efficient and practical Rabin-like cryptosystem without using the Jacobi symbol, redundancy in the message and avoiding the demands of extra information for finding the correct plaintext. Decryption outputs a unique plaintext without any decryption failure. In addition, decryption only requires a single prime. Furthermore, the decryption procedure only computes a single modular exponentiation instead of two modular exponentiation executed by other Rabin variants. As a result, this reduces the computational effort during the decryption process. Moreover the Novak’s side channel attack is impractical over the proposed Rabin-like cryptosystem. In parallel, we prove that the Rabin-p cryptosystem is indeed as intractable as the integer factorization problem

EXPLORING CONFIDENTIALITY AND PRIVACY OF IMAGE IN CLOUD COMPUTING

With the increasing popularity of cloud computing, clients are storing their data in cloud servers and are using “software as a service” for computing services. However, clients’ data may be sensitive, critical, and private, and processing such data with cloud servers may result in losing data privacy or compromising data confidentiality. Some cloud servers may be dishonest, while malicious entities may compromise others. In order to protect data privacy and confidentiality, clients need to be able to hide their actual data values and send the obfuscated values to cloud servers. This thesis deals with the outsourcing of computing to cloud servers, in which clients’ images can be computed and stored. This thesis proposes a technique that obfuscates images before sending them to servers, so these servers can perform computations on images without knowing the actual images. The proposed technique is expected to ensure data privacy and confidentiality. Servers will not be able to identify an individual whose images are stored and manipulated by the server. In addition, our approach employs an obfuscating technique to maintain the confidentiality of images, allowing cloud servers to compute obfuscated data accurately without knowing the actual data value, thus supporting privacy and confidentiality. The proposed approach is based on the Rabin block cipher technique, which has some weaknesses, however. The main drawback is its decryption technique, which results in four values, and only one of these values represents the actual value of plain data. Another issue is that the blocking technique requires a private key for each block that requires a high-computing effort; requiring one private key for each block of data demands that a great number of keys be stored by the client. As a result, it decreases the robustness of the Rabin block cipher. This thesis proposes additional techniques to overcome some of the weaknesses of the Rabin block cipher by introducing some new features, such as tokenization, a digit counter, and a set of blocks. The new technique increases the privacy of data and decreases the computational complexity by requiring fewer private keys. The new features have been implemented in image processing in order to demonstrate their applicability. However, in order to apply our approach to images, we must first apply some preprocessing techniques on images to make them applicable to being obfuscated by our proposed obfuscating system

Efficient methods to overcome Rabin cryptosystem decryption failure

Rabin cryptosystem is an efficient factoring-based scheme, however, its decryption produces 4-to-1 output, which leads to decryption failure. In this work, in order to overcome the 4-to-1 decryption problem for the Rabin cryptosystem, we propose two distinct methods using the modulus of the type N=p2q coupled with the restriction on the plaintext space M. In the first method, the plaintext space is limited to M ∈ Zpq. For the second method, we restrict the plaintext in the range of M ∈ (0,22n−2). Importantly, we prove that the decryption output of the proposed methods is unique and without decryption failure. The results in this work indicate that the decryption problem of Rabin cryptosystem is overcome

Instantiability of RSA-OAEP under Chosen-Plaintext Attack

We show that the widely deployed RSA-OAEP encryption scheme of Bellare and Rogaway (Eurocrypt 1994), which combines RSA with two rounds of an underlying Feistel network whose hash ({\em i.e.}, round) functions are modeled as random oracles, meets indistinguishability under chosen-plaintext attack (IND-CPA) in the {\em standard model} based on simple, non-interactive, and non-interdependent assumptions on RSA and the hash functions. To prove this, we first give a result on a more general notion called ``padding-based\u27\u27 encryption, saying that such a scheme is IND-CPA if (1) its underlying padding transform satisfies a ``fooling condition against small-range distinguishers on a class of high-entropy input distributions, and (2) its trapdoor permutation is sufficiently {\em lossy} as defined by Peikert and Waters (STOC 2008). We then show that the first round of OAEP satisfies condition (1) if its hash function is $t$-wise independent for $t$ roughly proportional to the allowed message length. We clarify that this result requires the hash function to be keyed, and for its key to be included in the public-key of RSA-OAEP. We also show that RSA satisfies condition (2) under the $\Phi$-Hiding Assumption of Cachin \emph{et al.}~(Eurocrypt 1999). This is the first {\em positive} result about the instantiability of RSA-OAEP. In particular, it increases confidence that chosen-plaintext attacks are unlikely to be found against the scheme. In contrast, RSA-OAEP\u27s predecessor in PKCS \#1 v1.5 was shown to be vulnerable to such attacks by Coron {\em et al}.~(Eurocrypt 2000)

Modified Parameter Attacks: Practical Attacks against CCA2 Secure Cryptosystems and Countermeasures

We introduce the concept of Modified Parameter Attacks, a natural extension of the idea of Adapative Chosen Ciphertext Attacks (CCA2) under which some CCA2 secure systems can be shown to be insecure. These insecurities can be addressed at the application level, but can also be addressed when cryptographic schemes are being designed. We survey some existing CCA2 secure systems which are vulnerable to this attack and suggest practical countermeasures

Identification Based Encryption with RSA-OAEP. Using SEM and Without

In this article we show how we can integrate the RSA (RSA-OAEP) into the IBE. Our prove can be make with either Standard Model or Random Oracle. We firstly develop the basic ideas made in this direction, so that to create a novel scheme with which we can signs and crypt at the same time. Then we give our new approach which conserves properly the syntax of the RSA classic. Additionally we compare our authentication with the signature of Shamir. More than that, in the RSA-IBE there is the problem of relating the exponent with an identity. Even if, there was some proposals in this direction, but they operate only with the Random Oracle. And in this article we will response to question of Xuhua Ding and Gene Tsudik, in order to propose an efficient exponent for an RSA-IBE. In the end of the article we give a useful appendix

Asymmetric cryptography and practical security, Journal of Telecommunications and Information Technology, 2002, nr 4

Since the appearance of public-key cryptography in Diffie-Hellman seminal paper, many schemes have been proposed, but many have been broken. Indeed, for many people, the simple fact that a cryptographic algorithm withstands cryptanalytic attacks for several years is considered as a kind of validation. But some schemes took a long time before being widely studied, and maybe thereafter being broken. A much more convincing line of research has tried to provide “provable” security for cryptographic protocols, in a complexity theory sense: if one can break the cryptographic protocol, one can efficiently solve the underlying problem. Unfortunately, very few practical schemes can be proven in this so-called “standard model” because such a security level rarely meets with efficiency. A convenient but recent way to achieve some kind of validation of efficient schemes has been to identify some concrete cryptographic objects with ideal random ones: hash functions are considered as behaving like random functions, in the so-called “random oracle model”, block ciphers are assumed to provide perfectly independent and random permutations for each key in the “ideal cipher model”, and groups are used as black-box groups in the “generic model”.In this paper, we focus on practical asymmetric protocols together with their “reductionist” security proofs. We cover the two main goals that public-key cryptography is devoted to solve: authentication with digital signatures, and confidentiality with public-key encryption schemes