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Quantum Bit Commitment. Christian Schaffner DAIMI – Department of Computer Science BRICS – Basic Research in Computer Science NAT-årsfest June 3, 2005. Alice. Bob. Alice & Bob. *!¤. Alice. Bob. Divorce Problems. *!¤. who gets the house?. Alice. Bob.

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slide1

Quantum Bit Commitment

Christian Schaffner

DAIMI – Department of Computer Science

BRICS – Basic Research in Computer Science

NAT-årsfest

June 3, 2005

A A R H U S U N I V E R S I T E T

DAIMI – Department of Computer Science

BRICS – Basic Research in Computer Science

alice bob

Alice

Bob

Alice & Bob

*!¤

A A R H U S U N I V E R S I T E T

DAIMI – Department of Computer Science

BRICS – Basic Research in Computer Science

divorce problems

Alice

Bob

Divorce Problems

*!¤

who gets the house?

A A R H U S U N I V E R S I T E T

DAIMI – Department of Computer Science

BRICS – Basic Research in Computer Science

coin flipping over the telephone

Alice

Bob

Coin-Flipping over the Telephone

It’s tails,

I get

the house!

A A R H U S U N I V E R S I T E T

DAIMI – Department of Computer Science

BRICS – Basic Research in Computer Science

a coin flipping protocol

Alice

Bob

A Coin-Flipping Protocol

not random!

A A R H U S U N I V E R S I T E T

DAIMI – Department of Computer Science

BRICS – Basic Research in Computer Science

the solution

Alice

Bob

The Solution

A A R H U S U N I V E R S I T E T

DAIMI – Department of Computer Science

BRICS – Basic Research in Computer Science

the explanation

Alice

Bob

The Explanation

A A R H U S U N I V E R S I T E T

DAIMI – Department of Computer Science

BRICS – Basic Research in Computer Science

bit commitment scheme

commit

Alice

Bob

Bit-Commitment Scheme

Bob‘s

view

open

  • important cryptographic primitive
  • hiding
  • binding

A A R H U S U N I V E R S I T E T

DAIMI – Department of Computer Science

BRICS – Basic Research in Computer Science

particular bit commitment scheme

Alice

Bob

Particular Bit-Commitment Scheme

commit to 0

Bob‘s

view

(n MegaBytes)

commit to 1

bounded memory!

(n MB)

open

  • honest Alice needs: n
  • cheating Alice needs: 2¢n
  • Memorycheater< 2 ¢ Memoryhonest ) binding
  • perfectly hiding

A A R H U S U N I V E R S I T E T

DAIMI – Department of Computer Science

BRICS – Basic Research in Computer Science

quantum bit commitment scheme

Alice

Bob

Quantum Bit-Commitment Scheme

Bob‘s

view

measure qbits in basis a

n quantum bits

bounded quantum memory!

bounded memory!

open

classically:

Memorycheater< 2 ¢ Memhonest

  • perfectly hiding
  • honest Alice needs no quantum memory
  • Memorycheater< n/2 ) binding

A A R H U S U N I V E R S I T E T

DAIMI – Department of Computer Science

BRICS – Basic Research in Computer Science

the end

bounded quantum memory!

bounded quantum memory!

Alice

Bob

The End

*!¤

A A R H U S U N I V E R S I T E T

DAIMI – Department of Computer Science

BRICS – Basic Research in Computer Science