Applied Cryptography and Computer Security CSE 664 Spring 2020
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The Order of Encryption and Authentication for Protecting Communications (Or: How Secure Is SSL?)?
The Order of Encryption and Authentication for Protecting Communications (Or: How Secure is SSL?)? Hugo Krawczyk?? Abstract. We study the question of how to generically compose sym- metric encryption and authentication when building \secure channels" for the protection of communications over insecure networks. We show that any secure channels protocol designed to work with any combina- tion of secure encryption (against chosen plaintext attacks) and secure MAC must use the encrypt-then-authenticate method. We demonstrate this by showing that the other common methods of composing encryp- tion and authentication, including the authenticate-then-encrypt method used in SSL, are not generically secure. We show an example of an en- cryption function that provides (Shannon's) perfect secrecy but when combined with any MAC function under the authenticate-then-encrypt method yields a totally insecure protocol (for example, ¯nding passwords or credit card numbers transmitted under the protection of such protocol becomes an easy task for an active attacker). The same applies to the encrypt-and-authenticate method used in SSH. On the positive side we show that the authenticate-then-encrypt method is secure if the encryption method in use is either CBC mode (with an underlying secure block cipher) or a stream cipher (that xor the data with a random or pseudorandom pad). Thus, while we show the generic security of SSL to be broken, the current practical implementations of the protocol that use the above modes of encryption are safe. 1 Introduction The most widespread application of cryptography in the Internet these days is for implementing a secure channel between two end points and then exchanging information over that channel. -
Multi-Device for Signal
Multi-Device for Signal S´ebastienCampion3, Julien Devigne1, C´elineDuguey1;2, and Pierre-Alain Fouque2 1 DGA Maˆıtrisede l’information, Bruz, France [email protected] 2 Irisa, Rennes, France, [email protected], [email protected] Abstract. Nowadays, we spend our life juggling with many devices such as smartphones, tablets or laptops, and we expect to easily and efficiently switch between them without losing time or security. However, most ap- plications have been designed for single device usage. This is the case for secure instant messaging (SIM) services based on the Signal proto- col, that implements the Double Ratchet key exchange algorithm. While some adaptations, like the Sesame protocol released by the developers of Signal, have been proposed to fix this usability issue, they have not been designed as specific multi-device solutions and no security model has been formally defined either. In addition, even though the group key exchange problematic appears related to the multi-device case, group solutions are too generic and do not take into account some properties of the multi-device setting. Indeed, the fact that all devices belong to a single user can be exploited to build more efficient solutions. In this paper, we propose a Multi-Device Instant Messaging protocol based on Signal, ensuring all the security properties of the original Signal. Keywords: cryptography, secure instant messaging, ratchet, multi-device 1 Introduction 1.1 Context Over the last years, secure instant messaging has become a key application ac- cessible on smartphones. In parallel, more and more people started using several devices - a smartphone, a tablet or a laptop - to communicate. -
Universit`A Di Pisa Post Quantum Cryptography
Universit`adi Pisa Facolt`a di Scienze Matematiche, Fisiche e Naturali Corso di Laurea Magistrale in Fisica Anno Accademico 2013/2014 Elaborato Finale Post Quantum Cryptography Candidato: Relatori: Antonio Vaira Prof. Oliver Morsch Ing. Cristiano Borrelli Alla mia mamma Abstract I started my experience with cryptography within the Airbus environment working on this master thesis. I have been asked to provide a framework, or in other words, a big picture about present-day alternatives to the most used public key crypto-system, the RSA, that are supposed to be quantum resistant. The final application of my work eventually resulted in recommendations on how to handle the quantum threat in the near future. This was quite a complex task to accomplish because it involves a huge variety of topics but by physical background was really helpful in facing it. Not because of specific and previous knowledge but for the mathematical toolsacquired during the studies and especially for that attitude that belongs to out category that make us, physicist problem solver in a large variety of fields. Indeed I also tried to go a bit further with my studies. I took one of the most promising algorithm on my opinion, but not well known yet so unfeasible for a recommendation and therefore an implementation in the close future, and I tried to figure out how to enhance it from both a security and an operational point of view (how to increase the correctness ratio of the decryption and the speed of the cryptographic operations). It followed a period of time in which I improved my skills with few computing languages and in the end I decided to implement a toy model at a high level using an interface that already implements all the mathematical and algebraical structures used to build the model. -
A Novel Asymmetric Hyperchaotic Image Encryption Scheme Based on Elliptic Curve Cryptography
applied sciences Article A Novel Asymmetric Hyperchaotic Image Encryption Scheme Based on Elliptic Curve Cryptography Haotian Liang , Guidong Zhang *, Wenjin Hou, Pinyi Huang, Bo Liu and Shouliang Li * School of Information Science and Engineering, Lanzhou University, Lanzhou 730000, China; [email protected] (H.L.); [email protected] (W.H.); [email protected] (P.H.); [email protected] (B.L.) * Correspondence: [email protected] (G.Z.); [email protected] (S.L.); Tel.: +86-185-0948-7799 (S.L.) Abstract: Most of the image encryption schemes based on chaos have so far employed symmetric key cryptography, which leads to a situation where the key cannot be transmitted in public channels, thus limiting their extended application. Based on the elliptic curve cryptography (ECC), we proposed a public key image encryption method where the hash value derived from the plain image was encrypted by ECC. Furthermore, during image permutation, a novel algorithm based on different- sized block was proposed. The plain image was firstly divided into five planes according to the amount of information contained in different bits: the combination of the low 4 bits, and other four planes of high 4 bits respectively. Second, for different planes, the corresponding method of block partition was followed by the rule that the higher the bit plane, the smaller the size of the partitioned block as a basic unit for permutation. In the diffusion phase, the used hyperchaotic sequences in permutation were applied to improve the efficiency. Lots of experimental simulations and cryptanalyses were implemented in which the NPCR and UACI are 99.6124% and 33.4600% Citation: Liang, H.; Zhang, G.; Hou, respectively, which all suggested that it can effectively resist statistical analysis attacks and chosen W.; Huang, P.; Liu, B.; Li, S. -
Private Searching on Streaming Data∗
J. Cryptology (2007) 20: 397–430 DOI: 10.1007/s00145-007-0565-3 © 2007 International Association for Cryptologic Research Private Searching on Streaming Data∗ Rafail Ostrovsky Department of Computer Science and Department of Mathematics, University of California, Los Angeles, CA 90095, U.S.A. [email protected] William E. Skeith III Department of Mathematics, University of California, Los Angeles, CA 90095, U.S.A. [email protected] Communicated by Dan Boneh Received 1 September 2005 and revised 16 July 2006 Online publication 13 July 2007 Abstract. In this paper we consider the problem of private searching on streaming data, where we can efficiently implement searching for documents that satisfy a secret criteria (such as the presence or absence of a hidden combination of hidden keywords) under various cryptographic assumptions. Our results can be viewed in a variety of ways: as a generalization of the notion of private information retrieval (to more general queries and to a streaming environment); as positive results on privacy-preserving datamining; and as a delegation of hidden program computation to other machines. Key words. Code obfuscation, Public-key program obfuscation, Program obfus- cation, Crypto-computing, Software security, Database security, Public-key encryp- tion with special properties, Private information retrieval, Privacy-preserving keyword search, Secure algorithms for streaming data, Privacy-preserving datamining, Secure delegation of computation, Searching with privacy, Mobile code. 1. Introduction 1.1. Data Filtering for the Intelligence Community As our motivating example, we examine one of the tasks of the intelligence community, which is to collect “potentially useful” information from huge streaming sources of ∗ An abridged version appeared at CRYPTO 2005. -
The Cramer-Shoup Strong-RSA Signature Scheme Revisited
The Cramer-Shoup Strong-RSA Signature Scheme Revisited Marc Fischlin Johann Wolfgang Goethe-University Frankfurt am Main, Germany marc @ mi.informatik.uni-frankfurt.de http://www.mi.informatik.uni-frankfurt.de/ Abstract. We discuss a modification of the Cramer-Shoup strong-RSA signature scheme. Our proposal also presumes the strong RSA assump- tion (and a collision-intractable hash function for long messages), but |without loss in performance| the size of a signature is almost halved compared to the original scheme. We also show how to turn the signature scheme into a \lightweight" anonymous (but linkable) group identifica- tion protocol without random oracles. 1 Introduction Cramer and Shoup [CS00] have presented a signature scheme which is secure against adaptive chosen-message attacks under the strong RSA (aka. flexible RSA) assumption, and which does not rely on the random oracle model. For a 1024-bit RSA modulus and a 160-bit (hash value of a) message a signature has about 2200 bits. Cramer and Shoup also discuss a variation of their scheme which, in addition to the strong RSA assumption, requires the discrete-log as- sumption and which produces signatures of roughly half the length (about 1350 bits). Here, we show that we can achieve the same signature size under the strong RSA assumption only, even with a slightly improved performance than in the original strong-RSA-only case or the discrete-log & strong-RSA case. Our signature scheme also has the feature that for short messages, e.g., of 120 bits, a collision-intractable (or universal one-way) hash function becomes obsolete. -
Trivia: a Fast and Secure Authenticated Encryption Scheme
TriviA: A Fast and Secure Authenticated Encryption Scheme Avik Chakraborti1, Anupam Chattopadhyay2, Muhammad Hassan3, and Mridul Nandi1 1 Indian Statistical Institute, Kolkata, India [email protected], [email protected] 2 School of Computer Engineering, NTU, Singapore [email protected] 3 RWTH Aachen University, Germany [email protected] Abstract. In this paper, we propose a new hardware friendly authen- ticated encryption (AE) scheme TriviA based on (i) a stream cipher for generating keys for the ciphertext and the tag, and (ii) a pairwise in- dependent hash to compute the tag. We have adopted one of the ISO- standardized stream ciphers for lightweight cryptography, namely Triv- ium, to obtain our underlying stream cipher. This new stream cipher has a state that is a little larger than the state of Trivium to accommodate a 128-bit secret key and IV. Our pairwise independent hash is also an adaptation of the EHC or \Encode-Hash-Combine" hash, that requires the optimum number of field multiplications and hence requires small hardware footprint. We have implemented the design in synthesizable RTL. Pre-layout synthesis, using 65 nm standard cell technology under typical operating conditions, reveals that TriviA is able to achieve a high throughput of 91:2 Gbps for an area of 24:4 KGE. We prove that our construction has at least 128-bit security for privacy and 124-bit security of authenticity under the assumption that the underlying stream cipher produces a pseudorandom bit stream. Keywords: Trivium, stream cipher, authenticated encryption, pairwise independent, EHC, TriviA. 1 Introduction The emergence of Internet-of-Things (IoT) has made security an extremely im- portant design goal. -
Cryptanalysis of Globalplatform Secure Channel Protocols
Cryptanalysis of GlobalPlatform Secure Channel Protocols Mohamed Sabt1;2, Jacques Traor´e1 1 Orange Labs, 42 rue des coutures, 14066 Caen, France fmohamed.sabt, [email protected] 2 Sorbonne universit´es,Universit´ede technologie de Compi`egne, Heudiasyc, Centre de recherche Royallieu, 60203 Compi`egne,France Abstract. GlobalPlatform (GP) card specifications are the de facto standards for the industry of smart cards. Being highly sensitive, GP specifications were defined regarding stringent security requirements. In this paper, we analyze the cryptographic core of these requirements; i.e. the family of Secure Channel Protocols (SCP). Our main results are twofold. First, we demonstrate a theoretical attack against SCP02, which is the most popular protocol in the SCP family. We discuss the scope of our attack by presenting an actual scenario in which a malicious entity can exploit it in order to recover encrypted messages. Second, we inves- tigate the security of SCP03 that was introduced as an amendment in 2009. We find that it provably satisfies strong notions of security. Of par- ticular interest, we prove that SCP03 withstands algorithm substitution attacks (ASAs) defined by Bellare et al. that may lead to secret mass surveillance. Our findings highlight the great value of the paradigm of provable security for standards and certification, since unlike extensive evaluation, it formally guarantees the absence of security flaws. Keywords: GlobalPlatform, secure channel protocol, provable security, plaintext recovery, stateful encryption 1 Introduction Nowadays, smart cards are already playing an important role in the area of in- formation technology. Considered to be tamper resistant, they are increasingly used to provide security services [38]. -
The RSA Algorithm
The RSA Algorithm Evgeny Milanov 3 June 2009 In 1978, Ron Rivest, Adi Shamir, and Leonard Adleman introduced a cryptographic algorithm, which was essentially to replace the less secure National Bureau of Standards (NBS) algorithm. Most impor- tantly, RSA implements a public-key cryptosystem, as well as digital signatures. RSA is motivated by the published works of Diffie and Hellman from several years before, who described the idea of such an algorithm, but never truly developed it. Introduced at the time when the era of electronic email was expected to soon arise, RSA implemented two important ideas: 1. Public-key encryption. This idea omits the need for a \courier" to deliver keys to recipients over another secure channel before transmitting the originally-intended message. In RSA, encryption keys are public, while the decryption keys are not, so only the person with the correct decryption key can decipher an encrypted message. Everyone has their own encryption and decryption keys. The keys must be made in such a way that the decryption key may not be easily deduced from the public encryption key. 2. Digital signatures. The receiver may need to verify that a transmitted message actually origi- nated from the sender (signature), and didn't just come from there (authentication). This is done using the sender's decryption key, and the signature can later be verified by anyone, using the corresponding public encryption key. Signatures therefore cannot be forged. Also, no signer can later deny having signed the message. This is not only useful for electronic mail, but for other electronic transactions and transmissions, such as fund transfers. -
Post-Quantum TLS Without Handshake Signatures Full Version, September 29, 2020
Post-Quantum TLS Without Handshake Signatures Full version, September 29, 2020 Peter Schwabe Douglas Stebila Thom Wiggers Max Planck Institute for Security and University of Waterloo Radboud University Privacy & Radboud University [email protected] [email protected] [email protected] ABSTRACT Client Server static (sig): pk(, sk( We present KEMTLS, an alternative to the TLS 1.3 handshake that TCP SYN uses key-encapsulation mechanisms (KEMs) instead of signatures TCP SYN-ACK for server authentication. Among existing post-quantum candidates, G $ Z @ 6G signature schemes generally have larger public key/signature sizes compared to the public key/ciphertext sizes of KEMs: by using an ~ $ Z@ ss 6G~ IND-CCA-secure KEM for server authentication in post-quantum , 0, 00, 000 KDF(ss) TLS, we obtain multiple benefits. A size-optimized post-quantum ~ 6 , AEAD (cert[pk( ]kSig(sk(, transcript)kkey confirmation) instantiation of KEMTLS requires less than half the bandwidth of a ss 6~G size-optimized post-quantum instantiation of TLS 1.3. In a speed- , 0, 00, 000 KDF(ss) optimized instantiation, KEMTLS reduces the amount of server CPU AEAD 0 (application data) cycles by almost 90% compared to TLS 1.3, while at the same time AEAD 00 (key confirmation) reducing communication size, reducing the time until the client can AEAD 000 (application data) start sending encrypted application data, and eliminating code for signatures from the server’s trusted code base. Figure 1: High-level overview of TLS 1.3, using signatures CCS CONCEPTS for server authentication. • Security and privacy ! Security protocols; Web protocol security; Public key encryption. -
ECE596C: Handout #15
ECE596C: Handout #15 Key Distribution Electrical and Computer Engineering, University of Arizona, Loukas Lazos Abstract. In this lecture we describe different key distribution schemes for establishing a shared secret among two or multiple parties. Particularly we present the Diffie-Hellman key distribution scheme and the Blom’s key predistribution scheme. 1 Key Distribution Problem The key distribution problem (KDP) is the problem of establishing and maintaining security asso- ciations (shared secrets) between a network of n users connected via insecure links. The KDP can be classified into the following two stages. – Initialization: During the initialization phase, a trusted party also referred to as Trusted Au- thority (TA) distributes keying information to relevant parties in a secure manner. The keying material can be either used directly to encrypt data, or it can be used to establish new security associations. – Maintenance: During the maintenance phase, the TA, or the network users themselves renew relevant cryptographic secrets to maintain secrecy of the communications (How is maintenance different from the initialization phase?) For the initialization phase, key material can be either preloaded to the network entities before deployment, or can be issued using a temporary secure channel. Using the secure channel, the TA assigns long lived keys to network entities, that are usually only used to derive other keys and not to encrypt data (they are also called key encryption keys). Nodes who wish to securely communicate use their long lived keys to establish a session key that has a much shorter expiration time. Question What determines the expiration time of a key? What are the advantages of having a session key? Parameters considered when designing a key distribution scheme – Resistance to node compromise and collusion. -
Secure Channels Secure Channels • Example Applications – PGP: Pretty Good Privacy CS 161/194-1 – TLS: Transport Layer Security Anthony D
Main Points • Applying last week’s lectures in practice • Creating Secure Channels Secure Channels • Example Applications – PGP: Pretty Good Privacy CS 161/194-1 – TLS: Transport Layer Security Anthony D. Joseph – VPN: Virtual Private Network September 26, 2005 September 26, 2005 CS161 Fall 2005 2 Joseph/Tygar/Vazirani/Wagner What is a Secure Channel? Plaintext Plaintext Creating Secure Channels Encryption / Internet Encryption / • Authentication and Data Integrity Decryption Decryption Ciphertext and MAC – Use Public Key Infrastructure or third-party server to authenticate each end to the other • A stream with these security requirements: – Add Message Authentication Code for – Authentication integrity • Ensures sender and receiver are who they claim to be – Confidentiality • Confidentiality • Ensures that data is read only by authorized users – Data integrity – Exchange session key for encrypt/decrypt ops • Ensures that data is not changed from source to destination • Bulk data transfer – Non-repudiation (not discussed today) • Ensures that sender can’t deny message and rcvr can’t deny msg • Key Distribution and Segmentation September 26, 2005 CS161 Fall 2005 3 September 26, 2005 CS161 Fall 2005 4 Joseph/Tygar/Vazirani/Wagner Joseph/Tygar/Vazirani/Wagner Symmetric Key-based Symmetric Key-based Secure Channel Secure Channel Alice Bob • Sender (A) and receiver (B) share secret keys KABencrypt KABencrypt – One key for A è B confidentiality KABauth KABauth – One for A è B authentication/integrity Message MAC Compare? Message – Each message