Obfustopia Built on Secret-Key Functional Encryption Fuyuki Kitagawa (Tokyo Institute of Technology) Ryo Nishimaki (NTT Secure Platform Laboratories) Keisuke Tanaka(Tokyo Institute of Technology)
Our results Focus � Constructing indistinguishability obfuscation (IO) from secret-key functional encryption (SKFE) collusion-resistant IO SKFE for all circuits 1-key succinct SKFE
Obfuscation unintelligible preserving functionality Obfuscation obfuscated code program code Virtual-black-box (VBB) obfuscation is most natural and intuitive But, impossibility for VBB obfuscation L à Many works focus on an weaker notion indistinguishability obfuscation (IO) No impossibility J
Usefulness and difficulty of IO Many works constructed a wide variety of crypto primitives from IO many classical primitives, deniable encryption, collusion-resistant FE program watermarking
Usefulness and difficulty of IO Many works constructed a wide variety of crypto primitives from IO many classical primitives, deniable encryption, collusion-resistant FE program watermarking However, “IO from standard assumption” is still major open question little studied L All constructions rely on multi-linear maps…
Usefulness and difficulty of IO Many works constructed a wide variety of crypto primitives from IO many classical primitives, deniable encryption, collusion-resistant FE program watermarking However, “IO from standard assumption” is still major open question little studied L All constructions rely on multi-linear maps… To realize IO from mild assumptions, It’s important to find seemingly weaker primitives implying IO We have functional encryption
Functional encryption (FE) encryption key cloud data data data
Functional encryption (FE) encryption key cloud data data data master secret key functional key (decryption key function f tied to f)
Functional encryption (FE) encryption key only cloud data f(data) data data data master secret key functional key (decryption key function f tied to f)
Functional encryption (FE) encryption key only cloud data f(data) data data data master secret key ≠ � public-key (PKFE) functional key (decryption key function f � secret-key (SKFE) � tied to f)
Succinctness / Collusion-resistance u Ciphertext size γ (0 ≤ γ < 1) � � succinct , cipher data text (or size of enc circuit)
Succinctness / Collusion-resistance u Ciphertext size γ (0 ≤ γ < 1) � � succinct , cipher data text (or size of enc circuit) u # of issuable functional keys issuable unbounded keys à collusion-resistant … master issuable only 1 functional key à 1-key scheme secret key
Previous works exp loss [BV15, AJ15] 1-key IO succinct PKFE for all circuits
Previous works +PKE exp loss [BNPW16, KNT18] [BV15, AJ15] 1-key coll-resist IO succinct PKFE SKFE for all circuits + LWE or IBE [LPST16, BNPW16, KNT18] 1-key succinct SKFE
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