On the Security of IV Dependent Stream Ciphers

Total Page:16

File Type:pdf, Size:1020Kb

On the Security of IV Dependent Stream Ciphers On the Security of IV Dependent Stream Ciphers Côme Berbain and Henri Gilbert France Telecom R&D {[email protected]} research & development Stream Ciphers IV-less IV-dependent key K key K IV (initial value) number ? generator keystream keystream plaintext ⊕ ciphertext plaintext ⊕ ciphertext e.g. RC4, Shrinking Generator e.g. SNOW, Scream, eSTREAM ciphers well founded theory [S81,Y82,BM84] less unanimously agreed theory practical limitations: prior work [RC94, HN01, Z06] - no reuse of K numerous chosen IV attacks - synchronisation - key and IV setup not well understood IV setup – H. Gilbert (2) research & developement Orange Group Outline security requirements on IV-dependent stream ciphers whole cipher key and IV setup key and IV setup constructions satisfying these requirements blockcipher based tree based application example: QUAD incorporate key and IV setup in QUAD's provable security argument IV setup – H. Gilbert (3) research & developement Orange Group Security in IV-less case: PRNG notion m K∈R{0,1} number truly random VS generator g generator g g(K) ∈{0,1}L L OR Z ∈R{0,1} 1 input A 0 or 1 PRNG A tests number distributions: Adv g (A) = PrK [A(g(K)) = 1] − PrZ [A(Z) = 1] PRNG PRNG Advg (t) = maxA,T(A)≤t (Advg (A)) PRNG 80 g is a secure cipher ⇔ g is a PRNG ⇔ Advg (t < 2 ) <<1 IV setup – H. Gilbert (4) research & developement Orange Group Security in IV-dependent case: PRF notion stream cipher perfect random fct. IV∈ {0,1}n function generator VSOR g* gK G = {gK} gK(IV) q oracle queries • A 0 or 1 PRF gK g* A tests function distributions: Adv G (A) = Pr[A = 1] − Pr[A = 1] PRF PRF Adv G (t, q) = max A (Adv G (A)) PRF 80 40 G is a secure cipher ⇔ G is a PRF ⇔ Adv G (t < 2 ,2 ) << 1 IV setup – H. Gilbert (5) research & developement Orange Group Structure of the stream ciphers considered here IV (n bits) key & IV K setup typical KG structure initial state (m bits) state transition keystream function generation λ iterations output function keystream (L bits) IV setup – H. Gilbert (6) research & developement Orange Group Security: sufficient conditions IV IV key & IV F = {fK} setup is a PRF initial state ⇒ G = {g ο fK} is a PRF keystream g generation is a PRNG keystream keystream [informally]: the key & IV setup is a PRF and the keystream generator is a PRNG ⇒ the whole stream cipher is secure IV setup – H. Gilbert (7) research & developement Orange Group This is due to a simple composition theorem Composition of {fK} and g function F = {f } generator K ≡ G = {g ο fK} number g generator (comp. time Tg) PRF PRF PRNG Composition Theorem: Adv G (t,q) ≤ Adv F (t',q) + qAdv g (t') where t' = t + qTg IV setup – H. Gilbert (8) research & developement Orange Group Key & IV setup = PRF is "almost" a necessary condition IV (n bits) F = {f } K time TK&IV (key and IV setup) initial state (m bits) g time TKG (keystream generation) m first keystream bits TK&IV + TKG ≥ TPRF (where TPRF is the time needed by the fastest n-bit to m-bit PRF) For a fast cipher,TKG is small, so TK&IV cannot be much lower than TPRF IV setup – H. Gilbert (9) research & developement Orange Group Key & IV setup: candidate PRF constructions Block cipher based (not detailed here) Examples: LEX (based on AES), Sosemanuk (based on Serpent) Pros: more conservative than many existing constructions Cons: heterogeneous construction ⇒ increased implementation complexity (except for LEX) Tree based (detailed in the sequel) Example: QUAD Conducting idea: re-use essentially the same PRNG as in the keystream generation Pros: low implementation complexity Cons: relatively slow IV setup – H. Gilbert (10) research & developement Orange Group Tree based construction [GGM86] m-bit to 2m-bit PRNG f ⇒ n-bit to m-bit PRF F = {fy} y (parameter) (m bits) f x1 = 0 0 1 f f f x = 1 0 1 (2m bits) 2 f f x3 = 1 0 1 x f f (input) f xn-1= 0 0 1 f f x = 1 n 0 1 fy(x) PRF PRNG Theorem[≈GGM86]: Adv F (t,q) ≤ nqAdv f (t') where t' = t + q(n+1)Tf IV setup – H. Gilbert (11) research & developement Orange Group Tree based key & IV setup truncated IV-less cipher⇒ key and IV setup K m-bit state f IV1 0 1 f f f IV 0 1 2 m-bit sequence 2 f f IV3 0 1 IV f f (input) f IVn-1 0 1 f f IVn Is this practical? 0 1 f (IV) Cons: relatively slow. If |IV|=80 bits and |state|=160 bits, K key & IV setup ≡ generation of 3200 keystream bytes Pros: very low extra implementation complexity in hardware IV setup – H. Gilbert (12) research & developement Orange Group The Stream Cipher QUAD [BGP06] Based on the multivariate quadratic problem (MQ) Given a system of m quadratic equations in n variables over GF(q) k k k Qk (x1 ,..., xn ) = ∑αi,j xi x j + ∑βi xi + γ = yk ,k = 1,...,m i≤j i Find a solution n (if any) x = (x1 ,..., x n ) ∈ GF(q) NP hard even over GF(2) best solving algorithms so far are exponential [Faugère, Bardet] QUAD iterates a fixed quadratic function S S keystream IV setup – H. Gilbert (13) research & developement Orange Group QUAD: keystream generation n internal state: x = (x1 ,..., xn ) ∈ GF(q) fixed public quadratic function S: n var., m = tn eq. (typically 2n eq.) (n bits) q = 2 S recommended parameters: q=2, n=160 bits, t=2 IV setup – H. Gilbert (14) research & developement Orange Group Security argument for the keystream generation Keystream generation, GF(2) case initial state (n bits) number λ iterations of S generator g keystream (L bits) Th [BGP06]: in the GF(2) case, if there exists a distinguisher for g allowing to distinguish a sequence of L = λ ( t − 1 ) n keystream bits associated with a random quadratic systems S and a random initial state value x in time T with advantage ε, then there is an MQ solver that n2λ2T ε solves a random instance of MQ in time T'≅ O( ) with probabilityε'= . ε2 22 λ Example of application: q=2, n = 350 bits, t = 2, L=240, T=280, ε = 1% (no such concrete reduction for the recommend value n = 160) IV setup – H. Gilbert (15) research & developement Orange Group QUAD: Key and IV Setup uses two public quadratic functions S0 and S1 of n eq. in n var. each set x with the key K for each IV bit IVi: tree based construction • if IVi = 0 then update x with S0(x) • if IVi = 1 then update x with S1(x) runup: clock the cipher n times without outputting the keystream typical key and IV lengths: 160 bits each IV setup – H. Gilbert (16) research & developement Orange Group Extending the proof to the whole cipher Whole cipher, GF(2) case IV (n bits) t =2 L + n 2 function λ iterations of S (λ = ) G={gofK} generator n keystream (L bits) Th: in the GF(2) case, if there exists a (T,q) PRF-distinguisher for the family G of IV to keystream functions associated with a random key and a random quadratic systems S with PRF-advantage ε, then there is an MQ solver that solves a random instance of MQ in time n2λ2q2T ε T'≅ O( ) with probability at least ε ' = 3 . ε 2 3.2 qλ Example of application: q=2, n = 760 bits, t = 2, L=240, T=280, ε = 1% IV setup – H. Gilbert (17) research & developement Orange Group Conclusions Requirements: a PRF is needed Conservative IV setup seems demanding w.r.t. computational complexity is not demanding w.r.t. implementation complexity "Provable security" can be extended to IV-dependent stream ciphers IV setup – H. Gilbert (18) research & developement Orange Group.
Recommended publications
  • 9/11 Report”), July 2, 2004, Pp
    Final FM.1pp 7/17/04 5:25 PM Page i THE 9/11 COMMISSION REPORT Final FM.1pp 7/17/04 5:25 PM Page v CONTENTS List of Illustrations and Tables ix Member List xi Staff List xiii–xiv Preface xv 1. “WE HAVE SOME PLANES” 1 1.1 Inside the Four Flights 1 1.2 Improvising a Homeland Defense 14 1.3 National Crisis Management 35 2. THE FOUNDATION OF THE NEW TERRORISM 47 2.1 A Declaration of War 47 2.2 Bin Ladin’s Appeal in the Islamic World 48 2.3 The Rise of Bin Ladin and al Qaeda (1988–1992) 55 2.4 Building an Organization, Declaring War on the United States (1992–1996) 59 2.5 Al Qaeda’s Renewal in Afghanistan (1996–1998) 63 3. COUNTERTERRORISM EVOLVES 71 3.1 From the Old Terrorism to the New: The First World Trade Center Bombing 71 3.2 Adaptation—and Nonadaptation— ...in the Law Enforcement Community 73 3.3 . and in the Federal Aviation Administration 82 3.4 . and in the Intelligence Community 86 v Final FM.1pp 7/17/04 5:25 PM Page vi 3.5 . and in the State Department and the Defense Department 93 3.6 . and in the White House 98 3.7 . and in the Congress 102 4. RESPONSES TO AL QAEDA’S INITIAL ASSAULTS 108 4.1 Before the Bombings in Kenya and Tanzania 108 4.2 Crisis:August 1998 115 4.3 Diplomacy 121 4.4 Covert Action 126 4.5 Searching for Fresh Options 134 5.
    [Show full text]
  • Ascon (A Submission to CAESAR)
    Ascon (A Submission to CAESAR) Ch. Dobraunig1, M. Eichlseder1, F. Mendel1, M. Schl¨affer2 1IAIK, Graz University of Technology, Austria 2Infineon Technologies AG, Austria 22nd Crypto Day, Infineon, Munich Overview CAESAR Design of Ascon Security analysis Implementations 1 / 20 CAESAR CAESAR: Competition for Authenticated Encryption { Security, Applicability, and Robustness (2014{2018) http://competitions.cr.yp.to/caesar.html Inspired by AES, eStream, SHA-3 Authenticated Encryption Confidentiality as provided by block cipher modes Authenticity, Integrity as provided by MACs \it is very easy to accidentally combine secure encryption schemes with secure MACs and still get insecure authenticated encryption schemes" { Kohno, Whiting, and Viega 2 / 20 CAESAR CAESAR: Competition for Authenticated Encryption { Security, Applicability, and Robustness (2014{2018) http://competitions.cr.yp.to/caesar.html Inspired by AES, eStream, SHA-3 Authenticated Encryption Confidentiality as provided by block cipher modes Authenticity, Integrity as provided by MACs \it is very easy to accidentally combine secure encryption schemes with secure MACs and still get insecure authenticated encryption schemes" { Kohno, Whiting, and Viega 2 / 20 Generic compositions MAC-then-Encrypt (MtE) e.g. in SSL/TLS MAC M security depends on E and MAC E ∗ C T k Encrypt-and-MAC (E&M) ∗ e.g. in SSH E C M security depends on E and MAC MAC T Encrypt-then-MAC (EtM) ∗ IPSec, ISO/IEC 19772:2009 M E C provably secure MAC T 3 / 20 Tags for M = IV (N 1), M = IV (N 2), . ⊕ k ⊕ k are the key stream to read M1, M2,... (Keys for) E ∗ and MAC must be independent! Pitfalls: Dependent Keys (Confidentiality) Encrypt-and-MAC with CBC-MAC and CTR CTR CBC-MAC Nk1 Nk2 Nk` M1 M2 M` IV ··· EK EK ··· EK EK EK EK M1 M2 M` C1 C2 C` T What can an attacker do? 4 / 20 Pitfalls: Dependent Keys (Confidentiality) Encrypt-and-MAC with CBC-MAC and CTR CTR CBC-MAC Nk1 Nk2 Nk` M1 M2 M` IV ··· EK EK ··· EK EK EK EK M1 M2 M` C1 C2 C` T What can an attacker do? Tags for M = IV (N 1), M = IV (N 2), .
    [Show full text]
  • Stream Cipher Designs: a Review
    SCIENCE CHINA Information Sciences March 2020, Vol. 63 131101:1–131101:25 . REVIEW . https://doi.org/10.1007/s11432-018-9929-x Stream cipher designs: a review Lin JIAO1*, Yonglin HAO1 & Dengguo FENG1,2* 1 State Key Laboratory of Cryptology, Beijing 100878, China; 2 State Key Laboratory of Computer Science, Institute of Software, Chinese Academy of Sciences, Beijing 100190, China Received 13 August 2018/Accepted 30 June 2019/Published online 10 February 2020 Abstract Stream cipher is an important branch of symmetric cryptosystems, which takes obvious advan- tages in speed and scale of hardware implementation. It is suitable for using in the cases of massive data transfer or resource constraints, and has always been a hot and central research topic in cryptography. With the rapid development of network and communication technology, cipher algorithms play more and more crucial role in information security. Simultaneously, the application environment of cipher algorithms is in- creasingly complex, which challenges the existing cipher algorithms and calls for novel suitable designs. To accommodate new strict requirements and provide systematic scientific basis for future designs, this paper reviews the development history of stream ciphers, classifies and summarizes the design principles of typical stream ciphers in groups, briefly discusses the advantages and weakness of various stream ciphers in terms of security and implementation. Finally, it tries to foresee the prospective design directions of stream ciphers. Keywords stream cipher, survey, lightweight, authenticated encryption, homomorphic encryption Citation Jiao L, Hao Y L, Feng D G. Stream cipher designs: a review. Sci China Inf Sci, 2020, 63(3): 131101, https://doi.org/10.1007/s11432-018-9929-x 1 Introduction The widely applied e-commerce, e-government, along with the fast developing cloud computing, big data, have triggered high demands in both efficiency and security of information processing.
    [Show full text]
  • 2013 Summer Challenge Book List TM
    2013 Summer Challenge Book List TM www.scholastic.com/summer Ages 3-5 (By Title, Author and Illustrator) F ABC Drive, Naomi Howland F Corduroy, Don Freeman F Happy Birthday, Hamster, Cynthia Lord & Derek Anderson F ABC I Like Me!, Nancy Carlson F A Den is a Bed for a Bear, Becky Baines F Harold and the Purple Crayon, Crockett Johnson F The ABCs of Thanks and Please, Diane C. Ohanesian F Dolphin Baby!, Nicola Davies F Here Come the Girl Scouts!, Shana Corey & Hadley Hooper F Abuela, Arthur Dorros & Elisa Kleven F Don’t Worry, Douglas!, David Melling F Homer, Shelley Rotner & Diane Detroit F Alexander and the Terrible, Horrible, No Good, F The Dot, Peter H. Reynolds Very Bad Day, Judith Viorst & Ray Cruz F The House that George Built, Suzanne Slade F Exclamation Mark, Amy Krouse Rosenthal & Tom Lichtenheld F Alice the Fairy, David Shannon F A House is a House for Me, Family Pictures, Carmen Lomas Garza F Mary Ann Hoberman & Betty Fraser F Alphabet Under Construction, Denise Fleming F First the Egg, Laura Vaccaro Seeger F How Do Dinosaurs Say Happy Birthday?, F All Kinds of Families!, Mary Ann Hoberman F Five Little Monkeys Reading in Bed, Eileen Christelow Jane Yolen & Mark Teague F The Are You Ready for Kindergarten? F How Does Your Salad Grow?, Francie Alexander workbook series, Kumon Publishing F The Frog & Toad Are Friends, Arnold Lobel F How Georgie Radboum Saved Baseball, David Shannon F Baby Bear Sees Blue, Ashley Wolff F The Froggy books, Jonathan London & Frank Remkiewicz F Huck Runs Amuck, Sean F Bailey, Harry Bliss F The Geronimo Stilton series, Geronimo Stilton F I Am Small, Emma Dodd F Bats at the Beach, Brian Lies F Gilbert Goldfish Wants a Pet, Kelly DiPucchio & Bob Shea F I Read Signs, Ana Hoban F Bird, Butterfly, Eel, James Prosek F The Giving Tree, Shel Silverstein F If Rocks Could Sing, Leslie McGuirk F Brown Bear, Brown Bear, What Do You See?, F Gone with the Wand, Margie Palatini Bill Martin Jr.
    [Show full text]
  • D-DOG: Securing Sensitive Data in Distributed Storage Space by Data Division and Out-Of-Order Keystream Generation †Jun Feng, †Yu Chen*, ‡Wei-Shinn Ku, §Zhou Su †Dept
    D-DOG: Securing Sensitive Data in Distributed Storage Space by Data Division and Out-of-order keystream Generation †Jun Feng, †Yu Chen*, ‡Wei-Shinn Ku, §Zhou Su †Dept. of Electrical & Computer Engineering, SUNY - Binghamton, Binghamton, NY 13902 ‡Dept. of Computer Science & Software Engineering, Auburn University, Auburn, AL 36849 §Dept. of Computer Science, Waseda University, Ohkubo 3-4-1, Shinjyuku, Tokyo 169-8555, Japan {jfeng3, ychen }@binghamton.edu, [email protected], [email protected] ∗ Abstract - Migrating from server-attached storage to system against the attacks/intrusion from outsiders. The distributed storage brings new vulnerabilities in creating a confidentiality and integrity of data are mostly achieved secure data storage and access facility. Particularly it is a using robust cryptograph schemes. challenge on top of insecure networks or unreliable storage However, such a security system is not robust enough to service providers. For example, in applications such as cloud protect the data in distributed storage applications at the computing where data storage is transparent to the owner. It is level of wide area networks. The recent progress of network even harder to protect the data stored in unreliable hosts. technology enables global-scale collaboration over More robust security scheme is desired to prevent adversaries heterogeneous networks under different authorities. For from obtaining sensitive information when the data is in their hands. Meanwhile, the performance gap between the execution instance, in the environment of peer-to-peer (P2P) file speed of security software and the amount of data to be sharing or the distributed storage in cloud computing processed is ever widening. A common solution to close the environment, it enables the concrete data storage to be even performance gap is through hardware implementation.
    [Show full text]
  • Scream on MSP430 07282015
    Implementation of the SCREAM Tweakable Block Cipher in MSP430 Assembly Language William Diehl George Mason University, Fairfax VA 22033, USA [email protected] Abstract. The encryption mode of the Tweakable Block Cipher (TBC) of the SCREAM Authenticated Cipher is implemented in the MSP430 microcontroller. Assembly language versions of the TBC are prepared using both precomputed tweak keys and tweak keys computed “on-the-fly.” Both versions are compared against published results for the assembly language version of SCREAM on the ATMEL AVR microcontroller, and against the C reference implementation in terms of performance and size. The assembly language version using precomputed tweak keys achieves a speedup of 1.7 and memory savings of 9 percent over the reported SCREAM implementation in the ATMEL AVR. The assembly language version using tweak keys computed “on-the-fly” achieves a speedup of 1.6 over the ATMEL AVR version while reducing memory usage by 15 percent. Keywords: Cryptography, encryption, MSP430, assembly, speed, efficiency 1 Introduction Authenticated ciphers combine the functionality of confidentiality and integrity into one algorithm. In 2014 the Competition for Authenticated Encryption: Security, Applicability, and Robustness (CAESAR) called for submission of authenticated cipher candidates [1]. CAESAR candidates are evaluated in terms of security, size, robustness, flexibility, and performance. Software reference implementations written in C code are required as part of Rounds One and Two submissions. Many of the Round One submissions contained the authors’ evaluations in both hardware and software. Additionally, several Round One submissions investigated the software performance of the authors’ algorithms on various types of platforms, including high-end CPU and resource-constrained microcontrollers suitable for embedded applications.
    [Show full text]
  • THE COLLECTED POEMS of HENRIK IBSEN Translated by John Northam
    1 THE COLLECTED POEMS OF HENRIK IBSEN Translated by John Northam 2 PREFACE With the exception of a relatively small number of pieces, Ibsen’s copious output as a poet has been little regarded, even in Norway. The English-reading public has been denied access to the whole corpus. That is regrettable, because in it can be traced interesting developments, in style, material and ideas related to the later prose works, and there are several poems, witty, moving, thought provoking, that are attractive in their own right. The earliest poems, written in Grimstad, where Ibsen worked as an assistant to the local apothecary, are what one would expect of a novice. Resignation, Doubt and Hope, Moonlight Voyage on the Sea are, as their titles suggest, exercises in the conventional, introverted melancholy of the unrecognised young poet. Moonlight Mood, To the Star express a yearning for the typically ethereal, unattainable beloved. In The Giant Oak and To Hungary Ibsen exhorts Norway and Hungary to resist the actual and immediate threat of Prussian aggression, but does so in the entirely conventional imagery of the heroic Viking past. From early on, however, signs begin to appear of a more personal and immediate engagement with real life. There is, for instance, a telling juxtaposition of two poems, each of them inspired by a female visitation. It is Over is undeviatingly an exercise in romantic glamour: the poet, wandering by moonlight mid the ruins of a great palace, is visited by the wraith of the noble lady once its occupant; whereupon the ruins are restored to their old splendour.
    [Show full text]
  • SCREAM Side-Channel Resistant Authenticated Encryption with Masking
    SCREAM Side-Channel Resistant Authenticated Encryption with Masking Vincent Grosso1∗ Ga¨etanLeurent2 Fran¸cois-Xavier Standaert1y Kerem Varici1z Anthony Journault1∗ Fran¸coisDurvaux1∗ Lubos Gaspar1z St´ephanieKerckhof1 1 ICTEAM/ELEN/Crypto Group, Universit´ecatholique de Louvain, Belgium. 2 Inria, EPI Secret, Rocquencourt, France. Contact e-mail: [email protected] Version 3 (Second Round Specifications), August 2015. Abstract This document defines the authenticated encryption (with associated data) algorithm SCREAM. It is based on Liskov et al.'s Tweakable Authenticated Encryption (TAE) mode with the new tweakable block cipher Scream. The main desirable features of SCREAM are: • A simple and regular design allowing excellent performances on a wide range of architec- tures, in particular if masking is implemented as a side-channel countermeasure; • Inheriting from TAE, security beyond the birthday bound, i.e. a 128-bit security guarantee with up to 2128 bits of data processed with the same 128-bit key; • Low overheads for the authentication mode (e.g. no extra cipher calls to generate masks); • Fully parallelisable authenticated encryption with minimal ciphertext length. Updates from the first round candidate. • Fixing mistakes in the authenticated encryption mode leading to simple forgeries (as pointed out by Wang Lei and Sim Siang Meng [18]). When no associated data is present, the mode is now identical to TAE as originally described by Liskov et. al [19]. • Removal of the involutive family of authenticated encryption algorithm iSCREAM and its underlying block cipher iScream, which were not selected as second-round candidate. • Extension of the round constants from 8 to 16 bits (motivated by [14, 17]). • S-box with improved differential properties and algebraic degree (motivated by [4]).
    [Show full text]
  • Cryptographic and Combinatorial Properties of Boolean Functions and S-Boxes
    Synopsis of the thesis entitled Cryptographic and Combinatorial Properties of Boolean Functions and S-boxes by Kishan Chand Gupta Applied Statistics Unit Indian Statistical Institute 2004 under the supervision of Dr. Palash Sarkar Applied Statistics Unit Indian Statistical Institute 1 Introduction In this thesis we study combinatorial aspects of Boolean functions and S-boxes with impor- tant cryptographic properties and construct new functions possesing such properties. These have possible applications in the design of private key (symmetric key) cryptosystems. Symmetric key cryptosystems are broadly divided into two classes. 1. Stream Ciphers, 2. Block Ciphers. Some recent proposals of stream ciphers are SNOW [37], SCREAM [52], TURING [98], MUGI [117], HBB [102], RABBIT [9], HELIX [38] and some proposals of block ciphers are DES, AES, RC6 [97], MARS [12], SERPENT [6], TWOFISH [104]. In stream cipher cryptography a pseudorandom sequence of bits of length equal to the message length is generated. This sequence is then bitwise XOR-ed (addition modulo 2) with the message sequence and the resulting sequence is transmitted. At the receiving end, deciphering is done by generating the same pseudorandom sequence and again bitwise XOR- ing the cipher bits with the random bits. The seed of the pseudorandom bit generator is obtained from the secret key. Linear Feedback Shift Registers (LFSRs) are important building blocks in stream cipher systems. A standard model (see Figure 1) of stream cipher [109, 110, 34] combines the out- puts of several independent LFSR sequences using a nonlinear Boolean function to produce the keystream. Design and analysis of practical stream cipher was kept confidential for a long time.
    [Show full text]
  • Fault Analysis of Stream Ciphers
    Fault Analysis of Stream Ciphers Jonathan J. Hoch and Adi Shamir Department of Computer Science and Applied Mathematics, The Weizmann Institute of Science, Israel Abstract. A fault attack is a powerful cryptanalytic tool which can be applied to many types of cryptosystems which are not vulnerable to direct attacks. The research literature contains many examples of fault attacks on public key cryptosystems and block ciphers, but surprisingly we could not find any systematic study of the applicability of fault attacks to stream ciphers. Our goal in this paper is to develop general techniques which can be used to attack the standard constructions of stream ciphers based on LFSR’s, as well as more specialized techniques which can be used against specific stream ciphers such as RC4, LILI-128 and SOBER- t32. While most of the schemes can be successfully attacked, we point out several interesting open problems such as an attack on FSM filtered constructions and the analysis of high Hamming weight faults in LFSR’s. Keywords: Stream cipher, LFSR, fault attack, Lili-128, SOBER-t32, RC4. 1 Introduction 1.1 Background Attacks against cryptosystems can be divided into two classes, direct attacks and indirect attacks. Direct attacks include attacks against the algorithmic na- ture of the cryptosystem regardless of its implementation. Indirect attacks make use of the physical implementation of the cryptosystem and include a large va- riety of techniques which either give the attacker some ‘inside information’ on the cryptosystem (such as power or timing analysis) or some kind of influence on the cryptosystem’s internal state such as ionizing radiation flipping random bits in the device’s internal memory.
    [Show full text]
  • Mind the Gap - a Closer Look at the Security of Block Ciphers Against Differential Cryptanalysis
    Mind the Gap - A Closer Look at the Security of Block Ciphers against Differential Cryptanalysis Ralph Ankele1?, Stefan Kölbl2,3 1 Royal Holloway University of London, Egham, United Kingdom. [email protected] 2 DTU Compute, Technical University of Denmark, Denmark 3 Cybercrypt, Denmark. [email protected] Abstract. Resistance against differential cryptanalysis is an important design criteria for any modern block cipher and most designs rely on finding some upper bound on probability of single differential character- istics. However, already at EUROCRYPT’91, Lai et al. comprehended that differential cryptanalysis rather uses differentials instead of single characteristics. In this paper, we consider exactly the gap between these two approaches and investigate this gap in the context of recent lightweight cryptographic primitives. This shows that for many recent designs like Midori, Skinny or Sparx one has to be careful as bounds from counting the number of active S-boxes only give an inaccurate evaluation of the best differential distinguishers. For several designs we found new differential distinguish- ers and show how this gap evolves. We found an 8-round differential distinguisher for Skinny-64 with a probability of 2−56.93, while the best single characteristic only suggests a probability of 2−72. Our approach is integrated into publicly available tools and can easily be used when developing new cryptographic primitives. Moreover, as differential cryptanalysis is critically dependent on the distribution over the keys for the probability of differentials, we provide experiments for some of these new differentials found, in order to confirm that our estimates for the probability are correct.
    [Show full text]
  • Understanding How to Prevent Sensitive Data Exposure
    Understanding how to prevent Sensitive Data Exposure Dr Simon Greatrix Just Trust The Internet! • Lots of free advice • Opinions to suit all tastes • Also has pictures of cats! • Not responsible for the collapse of civilization (so far) • Google has excellent branding Top tips for a successful presentation! (according to the internet) • Start with a joke • Imagine the audience naked • Avoid showing emotion • Use images to jazz things up Obligatory famous historical data breaches ● 200,000 BCE to 6000 BCE : Tribal life with no privacy at all ● 600 BCE to 400CE: Ancient City culture view privacy as a bad thing ● 75 CE to 800 CE: There is no word for “privacy” in classical nor medieval“Where Latin people conceal their ways from one another … ● 1215 CE:there Fourth no Council one will Of ever Lateran rightly makes gain neitherconfession their mandatory due honour nor office nor the justice that is befitting” ● 1450 CE: First use of “privacy” in English. Socrates (470 to 399 BCE) ● 1700 CE: Solo beds ● 1890 CE: First use of “Right To Privacy” What are we actually expected to do? ● The Standards – OWASP – PCI-DSS ● The Tools – Ciphers – Hashes An aside: What is “strong encryption”? Source: https://www.keylength.com Is this really a good idea? https://xkcd.com/538/ Your Personal Information Please don’t send us your personal information. We do not want your personal information. We have a hard enough time keeping track of our own personal information, let alone yours. If you tell us your name, or any identifying information, we will forget it immediately.
    [Show full text]