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Two Secure Anonymous Proxy-based Data Storages * Olivier Blazy 1 - - PowerPoint PPT Presentation

Two Secure Anonymous Proxy-based Data Storages * Olivier Blazy 1 Xavier Bultel 2 Pascal Lafourcade 2 Universit de Limoges, Xlim, Limoges, France Clermont Universit Auvergne, LIMOS, Clermont-Ferrand, France July 29, 2016 SECRYPT 2016, Lisbon


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SLIDE 1

Two Secure Anonymous Proxy-based Data Storages *

Olivier Blazy1 Xavier Bultel2 Pascal Lafourcade2

Université de Limoges, Xlim, Limoges, France Clermont Université Auvergne, LIMOS, Clermont-Ferrand, France

July 29, 2016 SECRYPT 2016, Lisbon

*This research was conducted with the support of the “Digital Trust” Chair

from the University of Auvergne Foundation.

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 1 / 20

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SLIDE 2

Proxy Re-Encryption (PRE)

Alice (pka, ska) Bob (pkb, skb) Proxy

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 2 / 20

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SLIDE 3

Proxy Re-Encryption (PRE)

Alice (pka, ska) Bob (pkb, skb) Proxy re-key rkb→a

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 2 / 20

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SLIDE 4

Proxy Re-Encryption (PRE)

Alice (pka, ska) Bob Offline (rkb→a) Proxy

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 2 / 20

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SLIDE 5

Proxy Re-Encryption (PRE)

Alice (pka, ska) Bob Offline (rkb→a) Proxy c c = Epkb(m)

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 2 / 20

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SLIDE 6

Proxy Re-Encryption (PRE)

Alice (pka, ska) Bob Offline (rkb→a) Proxy c c = Epkb(m) c′ c′ = RErkb→a(c) = Epka(m)

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 2 / 20

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SLIDE 7

Proxy Re-Encryption (PRE)

Alice (pka, ska) Bob Offline (rkb→a) Proxy c c = Epkb(m) c′ c′ = RErkb→a(c) = Epka(m) m = Dska(c′)

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 2 / 20

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SLIDE 8

Proxy Re-Encryption (PRE)

Alice (pka, ska) Bob Offline (rkb→a) Proxy c c = Epkb(m) c′ c′ = RErkb→a(c) = Epka(m) m = Dska(c′) P learns nothing about m (IND-CPA).

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 2 / 20

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SLIDE 9

PRE History

Blaze et al. (1998) First definition of PRE. Ivan et al. (2003) Formal treatment. Ateniese et al. (2006) Unidirectional PRE. Canetti et al. (2007) CCA security. Libert et al. (2007) Unidirectional + CCA.

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 3 / 20

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SLIDE 10

PRE History

Blaze et al. (1998) First definition of PRE. Ivan et al. (2003) Formal treatment. Ateniese et al. (2006) Unidirectional PRE. New application: encrypted storage management. Canetti et al. (2007) CCA security. Libert et al. (2007) Unidirectional + CCA.

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 3 / 20

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SLIDE 11

PRE based storage

User (pku, sku) Proxy Owner (pko, sko) Encrypted storage

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 4 / 20

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SLIDE 12

PRE based storage

User (pku, sku) Proxy Owner (pko, sko) Encrypted storage re-key rko→u

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 4 / 20

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SLIDE 13

PRE based storage

User (pku, sku) rko→u Proxy Owner Offline Encrypted storage

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 4 / 20

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SLIDE 14

PRE based storage

User (pku, sku) rko→u Proxy Owner Offline Encrypted storage file c ? file c ? Check user rights

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 4 / 20

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SLIDE 15

PRE based storage

User (pku, sku) rko→u Proxy Owner Offline Encrypted storage c = Epko(m) c′ = Epku(m) c′ = RErko→u(c) m = Dsku(c′)

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 4 / 20

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SLIDE 16

PRE based storage

User (pku, sku) rko→u Proxy Owner Offline Encrypted storage c = Epko(m) c′ = Epku(m) c′ = RErko→u(c) m = Dsku(c′) Semi-trust proxy:

  • No info about m
  • P knows U id.
  • P knows U rights
  • P knows c

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 4 / 20

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SLIDE 17

PRE based storage

User (pku, sku) rko→u Proxy Owner Offline Encrypted storage c = Epko(m) c′ = Epku(m) c′ = RErko→u(c) m = Dsku(c′) Semi-trust proxy:

  • No info about m
  • P knows U id.
  • P knows U rights
  • P knows c

Goal: more privacy!

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 4 / 20

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SLIDE 18

PRE & anonymity?

Ateniese et al. (2009) Anonymous re-encryption key. Shao et al. (2012) Anonymity for recipient message. Zheng et al. (2014) Anonymous re-encryption key + CCA.

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 5 / 20

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PRE & anonymity?

Ateniese et al. (2009) Anonymous re-encryption key. Shao et al. (2012) Anonymity for recipient message. Zheng et al. (2014) Anonymous re-encryption key + CCA. → Only partial anonymity.

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 5 / 20

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SLIDE 20

Our idea

User Proxy Owner (pkgi, skgi) Encrypted storage member of the group i

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 6 / 20

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SLIDE 21

Our idea

User Proxy Owner (pkgi, skgi) Encrypted storage member of the group i Member key MSKi proxy key K

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 6 / 20

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SLIDE 22

Our idea

User (MSKi) K Proxy Owner Offline Encrypted storage

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 6 / 20

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Our idea

User (MSKi) K Proxy Owner Offline Encrypted storage file c ?

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 6 / 20

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SLIDE 24

Our idea

User (MSKi) K Proxy Owner Offline Encrypted storage c = Epkgi(m)

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 6 / 20

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SLIDE 25

Our idea

User (MSKi) K Proxy Owner Offline Encrypted storage c = Epkgi(m) User knows MSKi and c

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 6 / 20

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SLIDE 26

Our idea

User (MSKi) K Proxy Owner Offline Encrypted storage Randomization with r MSK′

i and c′

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 6 / 20

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SLIDE 27

Our idea

User (MSKi) K Proxy Owner Offline Encrypted storage Randomization with r MSK′

i and c′

MSK′

i, c′

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 6 / 20

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SLIDE 28

Our idea

User (MSKi) K Proxy Owner Offline Encrypted storage Randomization with r MSK′

i and c′

c′′ c′′ = REK,MSK′

i (c′) Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 6 / 20

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SLIDE 29

Our idea

User (MSKi) K Proxy Owner Offline Encrypted storage c′′ c′′ = REK,MSK′

i (c′)

m = Dr(c′′)

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 6 / 20

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Our idea

User (MSKi) K ???? Owner Offline Encrypted storage m = Dr(c′′) MSK′

i and c′

Semi-trust proxy:

  • No info about m
  • No info about U id.
  • No info about i
  • No info about c

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 6 / 20

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SLIDE 31

Our contribution

Two schemes:

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 7 / 20

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SLIDE 32

Our contribution

Two schemes: DRAS: Direct revocation mechanism: The owner can revoke anybody anytime. Pay-per-download model. Weak anonymity.

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 7 / 20

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SLIDE 33

Our contribution

Two schemes: DRAS: Direct revocation mechanism: The owner can revoke anybody anytime. Pay-per-download model. Weak anonymity. IRAS: Indirect revocation mechanism: the owner can revoke users periodically. Monthly-fee model. Full anonymity.

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 7 / 20

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SLIDE 34

1

introduction

2

DRAS

3

IRAS

4

Conclusion

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 8 / 20

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SLIDE 35

DRAS

P-Gen(P): generate proxy keys (PKP, SKP). G-Gen(P): generate group key (PKGj, SKGj). Join(SKGj, WL, Ui): generate a group member key MSKj

i.

Encrypt(PKGj, m): encrypt m for group j. Revoke(MSKj

i, BL): revoke a user.

Open(VIEW, WL): desanonymize a transaction. ProxyDec(Ui, P): decryption protocol between a user and the proxy.

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 9 / 20

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SLIDE 36

DRAS

Keys construction: Proxy keys (PKP, SKP) for an encryption scheme. Group key (PKG, SKG) = (gγ, γ). Member key MSK = (t, EncPKP( t

γ)).

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 10 / 20

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SLIDE 37

DRAS

Keys construction: Proxy keys (PKP, SKP) for an encryption scheme. Group key (PKG, SKG) = (gγ, γ). Member key MSK = (t, EncPKP( t

γ)).

The encryption algorithm is an ElGamal variant: Keys Secret sk = x, public pk = gx. Encryption Pick r and compute (C1, C2) = (pkr, gr · m). Decryption Compute m =

C2 C1/sk

1 Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 10 / 20

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SLIDE 38

DRAS: Decryption protocol

C = (C1, C2) = (gr·γ, gr · m) MSK = (MSK1, MSK2) = (t, EncPKP( t

γ))

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 11 / 20

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SLIDE 39

DRAS: Decryption protocol

C = (C1, C2) = (gr·γ, gr · m) MSK = (MSK1, MSK2) = (t, EncPKP( t

γ))

(PKP; MSK; C) (SKP; BL) s

$

← Z∗

p; B = (C1)s B,MSK2

− − − − − − − − → If MSK2 ∈ BL then abort; else w = DecSKP(MSK2) m =

C2 D(1/s·t) D

← − − − − − − − − D = (B)w = (Cs

1)

t γ = gs·r·t

=

gr·m gs·r·t· 1

s·t = gr·m

gr

Output m Output VIEW = MSK2.

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 11 / 20

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SLIDE 40

DRAS: Decryption protocol

C = (C1, C2) = (gr·γ, gr · m) MSK = (MSK1, MSK2) = (t, EncPKP( t

γ))

(PKP; MSK; C) (SKP; BL) s

$

← Z∗

p; B = (C1)s B,MSK2MSK2

− − − − − − − − → If MSK2 ∈ BL then abort; else w = DecSKP(MSK2) = t

γ

m =

C2 D(1/s·t) D

← − − − − − − − − D = (B)w = (Cs

1)

t γ = gs·r·t

=

gr·m gs·r·t· 1

s·t = gr·m

gr

Output m Output VIEW = MSK2. Proxy links user who uses two times the same member key

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 11 / 20

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SLIDE 41

1

introduction

2

DRAS

3

IRAS

4

Conclusion

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 12 / 20

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SLIDE 42

ElGamal is malleable

C = (gr, gx·r.m) C′ = ((gr)s, (gx·r.m)s) = (g(r·s), g(r·s)·x · ms). Decryption: m′ = ms = g(r·s)·x·(ms)

g(r·s)

. Difficult to link C and C′ (Diffie-Hellman problem). The message m is hidden.

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 13 / 20

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SLIDE 43

Indirect Revocation Anonymous Storage

O-Gen(P): generate owner (PKO, SKO). P-Gen(P): generate proxy key pair (PKP, SKP). G-Gen(P): generate group key pair (PKG, SKG). Join(SKGj, SKO, PKP): generate a group member key MSK. O-Update(SKO, PKO): update (PKO, SKO). U-Update(MSKj

i, SKO): update MSK.

Encrypt(PKGj, m): encrypt a message m. ProxyDec(Ui, P): decryption protocol between a user and the proxy.

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 14 / 20

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SLIDE 44

(Simplified) IRAS parameters

Keys constructions: P = (G1, G2, GT, g1, g2, e, PKE, S). Proxy keys (PKP, SKP) = (gp

2, p).

Group keys (PKG, SKG) = (gγ

1, γ).

Member key MSK = (gp·s

2 , gs 2 · g1/γ 2

).

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 15 / 20

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SLIDE 45

(Simplified) IRAS parameters

Keys constructions: P = (G1, G2, GT, g1, g2, e, PKE, S). Proxy keys (PKP, SKP) = (gp

2, p).

Group keys (PKG, SKG) = (gγ

1, γ).

Member key MSK = (gp·s

2 , gs 2 · g1/γ 2

). The encryption algorithm is an ElGamal bilinear variant: Keys Secret sk = x, public pk = gx

1.

Encryption Pick r and compute (C1, C2) = (pkr, e(g1, g2)r · m). Decryption Compute m =

C2 e(C1,g2)1/sk

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 15 / 20

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SLIDE 46

(Simplified) Decryption protocol

C = (C1, C2) = (gr·γ

1 , e(g1, g2)r · m)

MSK = (MSK1, MSK2) = (gp·s

2 , gs 2 · g

1 γ

2 )

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 16 / 20

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SLIDE 47

(Simplified) Decryption protocol

C = (C1, C2) = (gr·γ

1 , e(g1, g2)r · m)

MSK = (MSK1, MSK2) = (gp·s

2 , gs 2 · g

1 γ

2 )

(C; MSK) (p) α, β

$

← Z∗

p

MSK′ = (MSKα

1, MSKα 2)

C′

1 = Cβ 1 C′

1,MSK′

− − − − − − − − → D = e(gr·γ·β

1

,

MSK′

2

MSK′1/p

1 )

m =

C2 D

1 α·β =

e(g1,g2)r·m e(g1,g2)

r·α·β α·β

D

← − − − − − − − − = e(g1, g2)r·α·β

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 16 / 20

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SLIDE 48

Provable IRAS

Many tools to construct a provable scheme: Proof of a signature on MSK from MSK′. Revocation: The owner updates his signing key, but does not re-sign MSK. Damgård-ElGamal (CCA1). Smooth projective hash functions.

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 17 / 20

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SLIDE 49

1

introduction

2

DRAS

3

IRAS

4

Conclusion

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 18 / 20

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SLIDE 50

DRAS

Direct revocation. Simple and efficient scheme. CPA secure. Not fully anonymous.

IRAS

Indirect revocation. Not efficient, use complex tools to be provably secure. CPA secure. Fully anonymous.

Future work

Increase and simplify IRAS. Without Damgård-ElGamal and SPHF.

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 19 / 20

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SLIDE 51

Thank you for your attention. Questions?

Olivier Blazy, Xavier Bultel, Pascal Lafourcade (Université de Limoges, Xlim, Limoges, France, Clermont Université Auvergne, LIMOS, Cler Two Secure Anonymous Proxy-based Data Storages July 29, 2016 20 / 20