introduction to post quantum cryptography and learning
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Introduction to post-quantum cryptography and learning with errors Douglas Stebila Funding acknowledgements: Summer School on real-world crypto and privacy ibenik, Croatia June 11, 2018


  1. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 25 Search-decision equivalence • Easy fact : If the search LWE problem is easy, then the decision LWE problem is easy. • Fact : If the decision LWE problem is easy, then the search LWE problem is easy. • Requires calls to decision oracle • Intuition: test the each value for the first component of the secret, then move on to the next one, and so on. [Regev STOC 2005]

  2. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 26 Choice of error distribution • Usually a discrete Gaussian distribution of width for error rate • Define the Gaussian function • The continuous Gaussian distribution has probability density function

  3. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 27 Short secrets • The secret distribution was originally taken to be the uniform distribution • Short secrets : use • There's a tight reduction showing that LWE with short secrets is hard if LWE with uniform secrets is hard. [Applebaum et al., CRYPTO 2009]

  4. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 28 Toy example versus real-world example 8 4 1 11 10 5 5 9 5 2738 3842 3345 2979 … 3 9 0 10 2896 595 3607 1 3 3 2 377 1575 640 12 7 3 4 2760 6 5 11 4 … 3 3 5 0 640 × 8 × 15 bits = 9.4 KiB

  5. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 29 Ring learning with errors problem random 4 1 11 10 Each row is the cyclic shift of the row above 10 4 1 11 11 10 4 1 1 11 10 4 4 1 11 10 10 4 1 11 11 10 4 1

  6. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 30 Ring learning with errors problem random 4 1 11 10 Each row is the cyclic shift of the row above 3 4 1 11 … 2 3 4 1 with a special wrapping rule: x wraps to – x mod 13. 12 2 3 4 9 12 2 3 10 9 12 2 11 10 9 12

  7. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 31 Ring learning with errors problem random 4 1 11 10 Each row is the cyclic shift of the row above … with a special wrapping rule: x wraps to – x mod 13. So I only need to tell you the first row.

  8. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 32 Ring learning with errors problem 4 + 1 x + 11 x 2 + 10 x 3 random 6 + 9 x + 11 x 2 + 11 x 3 secret × 0 – 1 x + 1 x 2 + 1 x 3 small noise + 10 + 5 x + 10 x 2 + 7 x 3 =

  9. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 33 Ring learning with errors problem 4 + 1 x + 11 x 2 + 10 x 3 random secret × small noise + 10 + 5 x + 10 x 2 + 7 x 3 = Search ring-LWE problem: given blue , find red

  10. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 34 Search ring-LWE problem [Lyubashesky, Peikert, Regev; EUROCRYPT 2010, JACM 2013]

  11. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 35 Decision ring-LWE problem

  12. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 36 Module learning with errors problem random secret small noise p 11 p 12 p 13 p 14 p 21 p 22 p 23 p 24 × + = p 31 p 32 p 33 p 34 p 41 p 42 p 43 p 44 p 51 p 52 p 53 p 54 Search Module-LWE problem: given blue , find red [Langlois & Stehlé, https://eprint.iacr.org/2012/090, DCC 2015]

  13. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 37 Ring-LWE versus Module-LWE Ring-LWE Module-LWE 4 1 11 10 3 4 1 11 2 3 4 1 12 2 3 4 9 12 2 3 10 9 12 2 11 10 9 12 Figure from https://eprint.iacr.org/2012/090.pdf

  14. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 38 Learning with rounding problem random secret 4 1 11 10 4 1 5 5 9 5 7 2 × = 3 9 0 10 2 0 1 3 3 2 11 3 12 7 3 4 5 1 6 5 11 4 12 4 3 3 5 0 8 2 Search LWR problem: given blue , find red [Banerjee, Peikert, Rosen EUROCRYPT 2012]

  15. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 39 LWE versus LWR LWE LWR • Noise comes from adding an • Noise comes from rounding to a explicit (Gaussian) error term smaller interval • Shown to be as hard as LWE when modulus/error ratio satisfies certain bounds https://eprint.iacr.org/2013/098, https://eprint.iacr.org/2015/769.pdf

  16. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 40 NTRU problem [Hoffstein, Pipher, Silverman ANTS 1998]

  17. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 41 Problems Learning with errors Module-LWE Search With uniform secrets Ring-LWE Learning with rounding Decision With short secrets NTRU problem

  18. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 42 Public key encryption from LWE

  19. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 43 Public key encryption from LWE Key generation Secret key A s e b + = Public key [Lindner, Peikert. CT-RSA 2011]

  20. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 44 Public key encryption from LWE Encryption s' A e' b' + = Ciphertext Receiver's public key q = m c s' b + v' v' + = e'' 2 Shared secret mask [Lindner, Peikert. CT-RSA 2011]

  21. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 45 q Public key encryption from LWE m c v' + = 2 Decryption Ciphertext q round b' s – = c m m ≈ v v 2 Almost the same shared secret mask as the sender used Secret key [Lindner, Peikert. CT-RSA 2011]

  22. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 46 Approximately equal shared secret The sender uses The receiver uses = s' (A s + e) + e'' = (s' A + e') s v' v = s' A s + (s' e + e'') = s' A s + (e' s) ≈ s' A s ≈ s' A s

  23. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 47 Regev's public key encryption scheme [Regev; STOC 2005]

  24. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 48 Encode/decode [Regev; STOC 2005]

  25. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 49 Lindner–Peikert public key encryption [Lindner, Peikert; CT-RSA 2011]

  26. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 50 Correctness

  27. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 51 Difference between Regev and Lindner–Peikert

  28. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 52 IND-CPA security of Lindner–Peikert Indistinguishable against chosen plaintext attacks [Lindner, Peikert; CT-RSA 2011]

  29. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 53 IND-CPA security of Lindner–Peikert → Decision-LWE → → Rewrite → [Lindner, Peikert; CT-RSA 2011]

  30. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 54 IND-CPA security of Lindner–Peikert → Decision-LWE → → Rewrite → Independent of hidden bit [Lindner, Peikert; CT-RSA 2011]

  31. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 55 Lattice-based KEM/PKEs submitted to NIST • BabyBear, MamaBear, PapaBear (ILWE) • CRYSTALS-Kyber (MLWE) • Ding Key Exchange (RLWE) • Emblem (LWE, RLWE) • FrodoKEM (LWE) • HILA5 (RLWE) • KCL (MLWE, RLWE) • KINDI (MLWE) • LAC (PLWE) • LIMA (RLWE) • Lizard (LWE, LWR, RLWE, RLWR) • Lotus (LWE) • NewHope (RLWE) • NTRU Prime (RLWR) • NTRU HRSS (NTRU) • NTRUEncrypt (NTRU) • Round2 (RLWR, LWR) • Saber (MLWR) • Titanium (PLWE) https://estimate-all-the-lwe-ntru-schemes.github.io/docs/

  32. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 56 Security of LWE-based cryptography "Lattice-based"

  33. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 57 Hardness of decision LWE – "lattice-based" worst-case gap shortest vector problem (GapSVP) poly-time [Regev05, BLPRS13] average-case decision LWE

  34. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 58 Lattices

  35. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 59 Lattices Discrete additive subgroup of Equivalently, integer linear combinations of a basis Diagram from http://www.cs.bris.ac.uk/pgrad/csjhvdp/files/bkz.pdf

  36. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 60 Lattices There are many bases for the same lattice – some short and orthogonalish, some long and acute. Diagram from http://www.cs.bris.ac.uk/pgrad/csjhvdp/files/bkz.pdf

  37. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 61 Closest vector problem Given some basis for the lattice and a target point in the space, find the closest lattice point. Diagram from http://www.cs.bris.ac.uk/pgrad/csjhvdp/files/bkz.pdf

  38. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 62 Shortest vector problem Given some basis for the lattice, find the shortest non-zero lattice point. Diagram from http://www.cs.bris.ac.uk/pgrad/csjhvdp/files/bkz.pdf

  39. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 63 Shortest vector problem

  40. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 64 Regev's iterative reduction [Regev; STOC 2005]

  41. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 65 Finding short vectors in lattices LLL basis reduction algorithm Block Korkine Zolotarev (BKZ) algorithm • Finds a basis close to Gram–Schmidt • Trade-off between runtime and basis quality • Polynomial runtime (in dimension), • In practice the best algorithm for but basis quality (shortness/orthogonality) is poor cryptographically relevant scenarios

  42. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 66 Solving the (approximate) shortest vector problem

  43. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 67 Picking parameters • Estimate parameters based on • Based on reductions: • Calculate required runtime for GapSVP runtime of lattice reduction or SVP based on tightness gaps and algorithms. constraints in each reduction • Pick parameters based on best known GapSVP or SVP solvers or known lower bounds • Reductions are typically non-tight (e.g., n 13 ); would lead to very large parameters • Based on cryptanalysis: • Ignore tightness in reductions. • Pick parameters based on best known LWE solvers relying on lattice solvers.

  44. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 68 KEMs and key agreement from LWE

  45. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 69 Key encapsulation mechanisms (KEMs)

  46. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 70 Key exchange protocols • A key exchange protocol is an interactive protocol carried out between two parties. • The goal of the protocol is to output a session key that is indistinguishable from random. • In authenticated key exchange protocols, the adversary can be active and controls all communications between parties; the parties are assumed to have authentically distributed trusted long-term keys out of band prior to the protocol. • In unauthenticated key exchange protocols, the adversary can be passive and only obtains transcripts of communications between honest parties. • IND-CPA KEMs can be viewed as a two flow unauthenticated key exchange protocol.

  47. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 71 Basic LWE key agreement (unauthenticated) Based on Lindner–Peikert LWE public key encryption scheme public: “big” A in Z q n x m Alice Bob secret: secret: random “small” s, e in Z q random “small” s', e' in Z q m n b = As + e b' = s'A + e' shared secret: shared secret: b's = s'As + e's ≈ s'As s'b ≈ s'As These are only approximately equal need rounding ⇒

  48. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 72 Rounding & reconciliation • Each coefficient of the polynomial is an integer modulo q • Treat each coefficient independently • Send a "reconciliation signal" to help with rounding • Techniques by Ding [Din12] and Peikert [Pei14] [Ding; eprint 2012] [Peikert; PQCrypto 2014]

  49. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 73 Basic rounding • Round either to 0 or q /2 • Treat q /2 as 1 This works This works q /4 most of the time: most of the time: prob. failure 2 -10 . prob. failure 2 -10 . round round q /2 0 Not good enough: Not good enough: to 1 to 0 we need exact key we need exact key agreement. agreement. 3 q /4

  50. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 74 Rounding and reconciliation (Peikert) Bob says which of two regions the value is in: or q /4 round to 1 q /4 If round q /2 0 to 0 3 q /4 q /2 0 q /4 d n u 0 o r If o t q /2 d 0 n u 3 q /4 o 1 r o t 3 q /4 [Peikert; PQCrypto 2014]

  51. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 75 Rounding and reconciliation (Peikert) • If | alice – bob | ≤ q /8, then this always works. q /4 alice bob alice round to 1 If round q /2 0 to 0 alice 3 q /4 • Security not affected: revealing or leaks no information [Peikert; PQCrypto 2014]

  52. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 76 Exact LWE key agreement (unauthenticated) public: “big” A in Z q n x m Alice Bob secret: secret: random “small” s, e in Z q random “small” s', e' in Z q m n b = As + e b' = s'A + e', or shared secret: shared secret: round( b's ) round( s'b )

  53. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 77 Exact ring-LWE key agreement (unauthenticated) public: “big” a in R q = Z q [ x ] / ( x n + 1) Alice Bob secret: secret: random “small” s, e in R q random “small” s’, e’ in R q b = a • s + e b’ = a • s’ + e’ , or shared secret: shared secret: round( s • b’ ) round( b • s’ )

  54. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 78 Public key validation • No public key validation possible for basic LWE/ring-LWE public keys • Key reuse in LWE/ring-LWE leads to real attacks following from search- decision equivalence • Comment in [Peikert, PQCrypto 2014] • Attack described in [Fluhrer, Eprint 2016] • Need to ensure usage is okay with just passive security (IND-CPA) • Or construct actively secure (IND-CCA) KEM/PKE/AKE using Fujisaki– Okamoto transform or quantum-resistant variant [Targhi–Unruh, TCC 2016] [Hofheinz et al., Eprint 2017]

  55. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 79 An example: FrodoKEM • KEM: Key encapsulation • Simple design: mechanism (simplified key • Free modular arithmetic exchange protocol) (q = 2 16 ) • Simple Gaussian sampling • Builds on basic (IND-CPA) LWE • Parallelizable matrix-vector public key encryption operations • Achieves IND-CCA security • No reconciliation against adaptive adversaries • Simple to code • By applying a quantum-resistant variant of the Fujisaki–Okamoto transform • Negligible error rate [Bos, Costello, Ducas, Mironov, Naehrig, Nikolaenko, Raghunathan, Stebila. ACM CCS 2016] [Alkim, Bos, Ducas, Easterbrook, LaMacchia, Longa, Mironov, Naehrig, Nikolaenko, Peikert, Raghunathan, Stebila. FrodoKEM NIST Submission, 2017]

  56. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 80 FrodoKEM construction IND-CPA secure FrodoPKE Pseudorandom A to save space FrodoPKE.KeyGen Basic LWE public key FrodoPKE.Enc FrodoPKE.Dec

  57. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 81 FrodoKEM construction IND-CPA secure FrodoPKE FrodoPKE.KeyGen FrodoPKE.Enc FrodoPKE.Dec Key transport using Basic LWE ciphertext public key encryption Shared secret

  58. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 82 FrodoKEM construction IND-CPA secure FrodoPKE FrodoPKE.KeyGen FrodoPKE.Enc FrodoPKE.Dec

  59. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 83 FrodoKEM construction IND-CPA secure IND-CCA secure FrodoPKE FrodoKEM Targhi–Unruh Quantum Fujisaki–Okamoto (QFO) transform FrodoPKE.KeyGen FrodoKEM.KeyGen FrodoPKE.Enc FrodoKEM.Encaps Adds well-formedness checks Extra hash value Implicit rejection FrodoPKE.Dec FrodoKEM.Decaps Requires negligible error rate

  60. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 84 FrodoKEM parameters FrodoKEM-640 FrodoKEM-976 Dimension n 640 976 Modulus q 2 15 2 16 Error distribution Approx. Gaussian Approx. Gaussian [-11, ..., 11], σ = 2.75 [-10, ..., 10], σ = 2.3 Failure probability 2 -148 2 -199 Ciphertext size 9,736 bytes 15,768 bytes Estimated security 2 143 classical 2 209 classical (cryptanalytic) 2 103 quantum 2 150 quantum Runtime 1.1 msec 2.1 msec

  61. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 85 Other applications of LWE

  62. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 86 Fully homomorphic encryption from LWE [Brakerski, Vaikuntanathan; FOCS 2011]

  63. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 87 Fully homomorphic encryption from LWE [Brakerski, Vaikuntanathan; FOCS 2011]

  64. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 88 Fully homomorphic encryption from LWE [Brakerski, Vaikuntanathan; FOCS 2011]

  65. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 89 Fully homomorphic encryption from LWE • Error conditions mean that the number of additions and multiplications is limited. • Multiplication increases the dimension (exponentially), so the number of multiplications is again limited. • There are techniques to resolve both of these issues. • Key switching allows converting the dimension of a ciphertext. • Modulus switching and bootstrapping are used to deal with the error rate.

  66. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 90 Digital signatures [Lyubashevsky 2011] "Rejection sampling" [Lyubashevsky; Eurocrypt 2012]

  67. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 91 Lattice-based signature schemes submitted to NIST • CRYSTALS-Dilithium (MLWE) • Falcon (NTRU) • pqNTRUsign (NTRU) • qTESLA (RLWE) https://estimate-all-the-lwe-ntru-schemes.github.io/docs/

  68. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 92 Post-quantum security models

  69. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 93 Post-quantum security models • Is the adversary quantum? • If so, at what stage(s) in the security experiment? • If so, can the adversary interact with honest parties (make queries) quantumly? • If so, and if the proof is in the random oracle model, can the adversary access the random oracle quantumly?

  70. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 94 Public key encryption security models IND-CCA Quantum security models • A is classical • "Future quantum" • A is quantum in line 5 but always has only classical access to Enc and Dec • "Post-quantum" • A is quantum in lines 2 and 5 but always has only classical access to Enc & Dec • "Fully quantum" • A is quantum in lines 2 and 5 and has quantum (superposition) access to Enc and Dec Symmetric crypto generally quantum-resistant, unless in fully quantum security models. [Kaplan et al., CRYPTO 2016]

  71. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 95 Quantum random oracle model • If the adversary is locally quantum (e.g., future quantum, post-quantum), should the adversary be able to query its random oracle quantumly? • No: We imagine the adversary only interacting classically with the honest system. • Yes: The random oracle model artificially makes the adversary interact with something (a hash function) that can implement itself in practice, so the adversary could implement it quantumly. • QROM seems to be prevalent these days • Proofs in QROM often introduce tightness gap • QROM proofs of Fujisaki–Okamoto transform from IND-CPA PKE to IND-CCA PKE very hot topic right now [Boneh et al, ASIACRYPT 2011 https://eprint.iacr.org/2010/428]

  72. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 96 Transitioning to PQ crypto

  73. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 97 Retroactive decryption • A passive adversary that records today's communication can decrypt once they get a quantum computer • Not a problem for some scenarios • Is a problem for other scenarios • How to provide potential post-quantum security to early adopters?

  74. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 98 Hybrid ciphersuites • Use pre-quantum and Why hybrid? post-quantum • Potential post-quantum security for early adopters algorithms together • Maintain compliance with • Secure if either one older standards (e.g. FIPS) remains unbroken • Reduce risk from Need to consider backward uncertainty on PQ compatibility for non-hybrid- assumptions/parameters aware systems

  75. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 99 Hybrid ciphersuites Key exchange Authentication Likely focus 1 Hybrid traditional + PQ Single traditional for next 10 years 2 Hybrid traditional + PQ Hybrid traditional + PQ 3 Single PQ Single traditional 4 Single PQ Single PQ

  76. Stebila • Intro to PQ crypto & LWE Summer school on real-world crypto & privacy • 2018-06-11 100 Hybrid post-quantum key exchange TLS 1.2 TLS 1.3 • Prototypes and software experiments: • Prototypes: • Bos, Costello, Naehrig, Stebila, S&P 2015 • liboqs OpenSSL fork • Bos, Costello, Ducas, Mironov, Naehrig, • https://github.com/open-quantum-safe/ope Nikolaenko, Raghunathan, Stebila, ACM CCS nssl/tree/OQS-master 2016 • Google Chrome experiment • Internet drafts: • https://security.googleblog.com/2016/07/experime • Whyte et al. nting-with-post-quantum.html • https://tools.ietf.org/html/draft-whyte-qsh-t • https://www.imperialviolet.org/2016/11/28/cecpq1. ls13-06 html • Shank and Stebila • liboqs OpenSSL fork • https://tools.ietf.org/html/draft-schanck-tls • https://openquantumsafe.org/ -additional-keyshare-00 • Microsoft OpenVPN fork • https://www.bleepingcomputer.com/news/microsof t/microsoft-adds-post-quantum-cryptography-to-

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