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一個新的代理簽章法 A New Proxy Signature Scheme

一個新的代理簽章法 A New Proxy Signature Scheme. 作 者 : 洪國寶 , 許琪慧 , 郭淑娟與邱文怡 報告者 : 郭淑娟. Outline. Definition Our proxy signature scheme Security analysis Conclusions. Definition. Proxy Signature [Mambo et al. 1996] A designed proxy signer signed message on behalf of the original signer. 

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一個新的代理簽章法 A New Proxy Signature Scheme

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  1. 一個新的代理簽章法A New Proxy Signature Scheme 作 者:洪國寶,許琪慧,郭淑娟與邱文怡 報告者:郭淑娟

  2. Outline • Definition • Our proxy signature scheme • Security analysis • Conclusions

  3. Definition • Proxy Signature [Mambo et al. 1996] A designed proxy signer signed message on behalf of the original signer.  Proxy Signer B  Original Signer A Delegation Message Proxy Signer B

  4. Our scheme--system parameters • Two public large primes p and q that q|p-1. • One public generator gZ*p with order q. • A public one way hash function h. • Each user i has a secret key xiZ*q and corresponding public key yi=gxi mod p. • Message m • Public delegation warrant w.

  5. Delegation warrant w • Proxy period. • The name of proxy and original signers. • The responsibility of proxy signer. • The key of certification including yA and yB.

  6. Our scheme — participants • A: Original signer • B: Proxy signer • V: Verifier

  7. Our scheme—three phases • Delegation phase • Signature phase • Verification phase

  8. Our scheme diagram Delegation phase Signature phase   Proxy certification Origin signer Proxy signer Verification phase  Proxy certification + Proxy signature Verifiers

  9. Delegation phase Step 1: Original signer A chooses a secret random number kZ*q , computes r =gk mod p . Step 2: A computes e =h(r, w) . Step 3: A computes s = k- xA e mod q. Step 4: A sends (e, s, w) to proxy signer B.

  10. Signature phase Step 1: Proxy signer B computes r’=gsyAe mod p Step 2: B checks h(r’, w)=ee, s, w is valid. Step 3: B chooses a secret random number tZ*q, computes = gt mod p. Step 4: B signs m by U= h(, m). Step 5: Bcomputes V= t-xB U-s mod q . Step 6: B sends ((e, s, w), (U,V,m)) to verifier V.

  11. Verification phase Step 1: Verifier V checks authentication for m. Step 2: Getting yA and yB from w, V computes r’= gsyAe mod p and ’= gv+syBU mod p. Step 3: If h(r’, w)=e  B is an authenticated proxy signer. Step 4: If U=h(’, m) (U, V, m) is valid.

  12. Security analysis • Attack1: Get the secret key xA of original signer A. • Attack2: Get the secret key xB of proxy signer B. • Attack3: Find the k choosing by A. • Attack4: Find the t choosing by B .

  13. Security analysis • Attack 5: Forge a valid proxy certification（e, s,w). • Attack 6: Forge a valid proxy signature（U, V, m).

  14. Conclusions • Original signer couldn’t forge proxy signer to generate proxy signature. • Only proxy signer can generate valid proxy signature. • Proxy signers could be identified efficiently. • The scheme is based on schnorr scheme. • Without secure channel.

  15. Ending

  16. Computation analysis

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