Attribution – NonCommercial - ShareAlike Altruistic Economics AE18: The Imaginary Friends Test v1.0 www.altruists.org Recommended Pre-requisite: AE10: Keeping Score A presentation by Dr. Robin Upton (2006-01-28) Available for download at www.altruists.org/ae14 Attribution – NonCommercial - ShareAlike Introduction to Imaginary Friends

Introduction to Imaginary Friends Altruistic Economics is a decentralised system, so users have a lot of autonomy... .  Artificial Construct  Real Individual User , such as the chance to create Imaginary Friends: Rewarding such Imaginary Friends would encourage deception. . F2F Network Growth

Each new member creates an online server and is linked in by friends. F2F Network Growth The Friend2Friend network grows organically, over real social relationships.   Each new member creates an online server and is linked in by friends.      The idea is, everyone has one online server. However,like WWW, there is no centre, noone in charge, no list of members. Sybil Attacks

The ‘Imaginary Friends’ Test Sybil Attacks ‘Sybil’ was the first person diagnosed with so-called ‘Multiple Personality Disorder’.       A Sybil Attack is an attempt to defraud an online system by using fake identities. The ‘Imaginary Friends’ Test

The ‘Imaginary Friends’ Test “Does it help to create ‘imaginary friends’?” 1. Imaginary Friends make no difference:  PASS:  No Incentive to Cheat 2. Imaginary Friends are a disadvantage:   3. Imaginary Friends are an advantage:   FAIL:  Incentive to Cheat . Media Sharing

Media Sharing Aysha Birbal Chris MEDIA SHARING is a project to network people who review files and then benefit from one another’s opinions. Aysha wants an opinion about the film ‘Chinese Whispers’… Aysha Birbal I value your opinion… I value your opinion… “Chinese Whispers” I know this film Chris How to quantify this process... ? Basic Framework

Basic Framework Aysha Birbal Chris Assume: Individuals make 2 sorts of evaluations: 1) ‘I value your opinion’ is quantified as V: 0<=V<=1 2) ‘I rate this File’ is quantified as R: 0<=R<=1 Individuals who don’t rate a file defer to their friends Friends of friends’ opinions are valued multiplicatively “Chinese Whispers” Birbal Aysha I value your opinion… 0.3 Chris opinion… 0.4 I rate this file… 0.8 So Aysha has one recommendation: Value=0.12 Rating=0.8 Combining Recommendations

Combining Recommendations Ratings are averaged according to value, to give a single figure. So, if Aysha has 4 recommendations: Value=0.15 Rating=0.6 Value=0.8 Rating=0.5 Value=0.08 Rating=0.6 Value=0.12 Rating=0.8 Note the high value of the 2nd rating, which means it dominates the others. 0.15×0.6+ 0.8×0.5+ 0.08×0.6+ 0.12×0.8 0.15+0.8+0.08+0.12 Weighted average = ≈ 0.55 Applying The Test

What if Chris made Imaginary Friends to rate the file for him? Applying The Test What if Chris made Imaginary Friends to rate the file for him? “Chinese Whispers” MBogoN Chris MBogo2 Rating = R I value your opinion… 1.0 MBogo1 Value=VB I value your opinion… 1.0 … Value=VB Rating=R … { N separate ratings have Overall value = NVB A Problem

Chris could use his Imaginary Friends to dominate the other ratings. A Problem So, if Aysha has 4 recommendations: Value=0.15 Rating=0.6 Value=0.8 Rating=0.5 Value=0.08 Rating=0.6 Value=NVB Rating=R If N is big enough, no one else’s ratings count! Chris could use his Imaginary Friends to dominate the other ratings. Imaginary friends can increase an individuals’ impact, so the algorithm fails the imaginary friends test. A Modification

A Modification To control the imaginary friends, we add a constraint to the model. “Chinese Whispers” MBogoN Chris MBogo2 Rating = R V1 MBogo1 Value=VB vN … v2 N friends give Chris N ratings, with a value of ∑Vf. f Let’s require ∑Vf=1 f Summary of The ‘Imaginary Friends’ Test

Modified Algorithm Examined With N>0 imaginary friends: As an individual: …} N such friends MBogof Rating = Rf “Chinese Whispers” Chris Vf VB VB Chris “Chinese Whispers” Rating = R Overall rating: Value= VB∑Vf Rating=∑VfRf f Single rating: Value=VB Rating=R Since ∑Vf=1, 1≥R,Rf≥0… f imaginary friends confer no advantage. So the modified algorithm passes the imaginary friends test. Modified Algorithm Examined

Summary of The Imaginary Friends Test Sybil Attacks are a feature of decentralised systems.  Creating Imaginary Friends should not confer any advantage: Applying the Imaginary Friends Test helps deduce algorithms suitable for decentralised systems. Recommended Further Reading: AE19: Preventing Abuse http://www.altruists.org/ae19