2. Christian Schaffner, PhD student NF-årsfest 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 Quantum Bit Commitment Christian Schaffner DAIMI – Department of Computer Science BRICS – Basic Research in Computer Science NAT-årsfest June 3, 2005

3. Christian Schaffner, PhD student NF-årsfest 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 *!¤

4. Christian Schaffner, PhD student NF-årsfest 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 who gets the house? *!¤ Divorce Problems

5. Christian Schaffner, PhD student NF-årsfest 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 Coin-Flipping over the Telephone It’s tails, I get the house! Alice Bob

6. Christian Schaffner, PhD student NF-årsfest 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 A Coin-Flipping Protocol Alice Bob not random!

7. Christian Schaffner, PhD student NF-årsfest 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 The Solution Alice Bob

8. Christian Schaffner, PhD student NF-årsfest 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 The Explanation Alice Bob

9. Christian Schaffner, PhD student NF-årsfest 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 Bob‘s view Bit-Commitment Scheme Alice Bob commit open important cryptographic primitive hiding binding

10. Christian Schaffner, PhD student NF-årsfest 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 Bob‘s view Particular Bit-Commitment Scheme open honest Alice needs:n cheating Alice needs:2¢n Memory cheater < 2 ¢ Memory honest ) binding perfectly hiding Alice Bob commit to 0 commit to 1 bounded memory! (n MegaBytes) (n MB)

11. Christian Schaffner, PhD student NF-årsfest 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 open Alice Bob Bob‘s view n quantum bits perfectly hiding honest Alice needs no quantum memory Memory cheater < n/2 ) binding bounded quantum memory! measure qbits in basis a bounded memory! classically: Memory cheater < 2 ¢ Mem honest Quantum Bit-Commitment Scheme

12. Christian Schaffner, PhD student NF-årsfest 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 The End Alice bounded quantum memory! Bob bounded quantum memory! *!¤

13. Christian Schaffner, PhD student NF-årsfest 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 Classically Impossible perfectly secure, without assumptions with classical communication with quantum communication Alice Bob Bob‘s view open commit hiding binding bounded memory!