Quantum Bit Commitment Christian Schaffner DAIMI – Department of Computer Science BRICS – Basic Research in Computer Science NAT-årsfest June 3, 2005 AARHUS UNIVERSITET DAIMI – Department of Computer Science BRICS – Basic Research in Computer Science Christian Schaffner, Ph. D student NF-årsfest 2005
Alice & Bob *!¤ Alice Bob AARHUS UNIVERSITET DAIMI – Department of Computer Science BRICS – Basic Research in Computer Science Christian Schaffner, Ph. D student NF-årsfest 2005
Divorce Problems *!¤ who gets the house? Alice Bob AARHUS UNIVERSITET DAIMI – Department of Computer Science BRICS – Basic Research in Computer Science Christian Schaffner, Ph. D student NF-årsfest 2005
Coin-Flipping over the Telephone Alice It’s tails, I get the house! Bob AARHUS UNIVERSITET DAIMI – Department of Computer Science BRICS – Basic Research in Computer Science Christian Schaffner, Ph. D student NF-årsfest 2005
A Coin-Flipping Protocol Alice not random! Bob AARHUS UNIVERSITET DAIMI – Department of Computer Science BRICS – Basic Research in Computer Science Christian Schaffner, Ph. D student NF-årsfest 2005
The Solution Alice Bob AARHUS UNIVERSITET DAIMI – Department of Computer Science BRICS – Basic Research in Computer Science Christian Schaffner, Ph. D student NF-årsfest 2005
The Explanation Alice Bob AARHUS UNIVERSITET DAIMI – Department of Computer Science BRICS – Basic Research in Computer Science Christian Schaffner, Ph. D student NF-årsfest 2005
Bit-Commitment Scheme commit Bob‘s view open Alice Bob • important cryptographic primitive • hiding • binding AARHUS UNIVERSITET DAIMI – Department of Computer Science BRICS – Basic Research in Computer Science Christian Schaffner, Ph. D student NF-årsfest 2005
Particular Bit-Commitment Scheme commit to 0 (n Mega. Bytes) commit to 1 Alice bounded memory! Bob‘s view (n MB) open Bob • honest Alice needs: n • cheating Alice needs: 2¢n • Memorycheater < 2 ¢ Memoryhonest ) binding • perfectly hiding AARHUS UNIVERSITET DAIMI – Department of Computer Science BRICS – Basic Research in Computer Science Christian Schaffner, Ph. D student NF-årsfest 2005
Quantum Bit-Commitment Scheme measure qbits in basis a Alice n quantum bits bounded memory! quantum memory! open Bob‘s view Bob classically: Memorycheater < 2 ¢ Memhonest • perfectly hiding • honest Alice needs no quantum memory • Memorycheater < n/2 ) binding AARHUS UNIVERSITET DAIMI – Department of Computer Science BRICS – Basic Research in Computer Science Christian Schaffner, Ph. D student NF-årsfest 2005
The End bounded quantum memory! *!¤ Alice Bob bounded quantum memory! AARHUS UNIVERSITET DAIMI – Department of Computer Science BRICS – Basic Research in Computer Science Christian Schaffner, Ph. D student NF-årsfest 2005
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