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sidebar hide from wikipedia the free encyclopedia resistance to a malicious network attack this article provides insufficient context for those unfamiliar with the subject please help improve the article by providing more context for the reader march 2022 learn how and when to remove this message proof of personhood pop is a means of resisting malicious attacks on peer to peer networks particularly attacks that use multiple fake identities otherwise known as a sybil attack decentralized online platforms are particularly vulnerable to such attacks by their very nature as notionally democratic and responsive to large voting blocks in pop each unique human participant obtains one equal unit of voting power and any associated rewards the term is used in cryptocurrency and blockchains as a parallel to proof of work proof of stake and other consensus mechanisms which attempt to distribute voting power and rewards to participants proportionately to an investment of resources background edit the problem of sybil attacks using many virtual identities has been recognized for decades as a fundamental challenge for distributed systems that expect each human user to have only one account or identity 1 captchas attempt to rate limit automated sybil attacks by using automated turing tests to distinguish humans from machines creating accounts or requesting services even when successful in this goal however captchas allow one human to obtain multiple accounts or shares of a resource simply by solving multiple captchas in succession and thus do not satisfy the one per person goal in pop aside from captchas allowing people to obtain multiple users there are additional complications many users who are visually impaired or have learning disabilities may struggle to complete the puzzles additionally some recently developed ai has succeeded in solving the captcha issue 2 distributed systems could require users to authenticate using strong identities verified by a government or trusted third party using an identity verification service or self sovereign identity system for example but strong identification requirements conflict with privacy and anonymity and increase barriers to entry 3 one approach proposed to create anonymous but one per person credentials for use in distributed systems is pseudonym parties in which participants gather periodically at in person events and leverage the fact that humans can physically be in only one place at a time 4 in 2014 vitalik buterin proposed the problem of creating a unique identity system for cryptocurrencies which would give each human user one and only one anti sybil participation token 5 non primary source needed in 2017 the term proof of personhood was proposed for an approach based on pseudonym parties 6 approaches edit a variety of approaches to implementing proof of personhood have been proposed some in experimental deployment 7 in person events edit the approach originally proposed by borge et al was to use in person pseudonym parties as a basis to create anonymous one per person tokens periodically without requiring any form of identity verification 4 6 the encointer project adapts this approach by asking participants to meet in small groups simultaneously at randomly chosen places to verify each other s physical presence 8 one drawback of this approach is the inconvenience to participants of going to designated physical locations at specific times especially for participants with conflicting responsibilities at those times another issue is the challenge of organizing federated pseudonym parties in multiple locations simultaneously while allowing each group to verify that all other groups are organized honestly without inflating the number of digital credentials they issue citation needed social networks edit another approach related to the pgp web of trust relies on users forming a social network to verify and attest to each other s identities 9 uniqueid incorporates biometric verification into the social network approach 10 one criticism of the social network approach is that there is no straightforward way for a participant to verify that a social connection has not created other sybil identities connected to and verified by other disjoint sets of social contacts a related challenge is that sybil detection based on graph analysis make certain assumptions about the behavior of a sybil attacker and it is not clear that real world social networks satisfy these assumptions 11 finally graph based sybil detection algorithms tend to be able to detect only large densely clustered groups of sybil nodes in a social network leaving small scale attacks difficult or impossible to distinguish by graph structure alone from legitimate users connectivity structures citation needed strong identities edit another approach requires participants to have verified identities but to hide or anonymize those identities in subsequent use one criticism of this approach is the privacy and surveillance risks inherent in such databases especially biometric databases and the level of trust users must place in the verification service for both sybil protection and privacy of their identity information other critics highlight that facial recognition systems fail on a global scale due to insufficient facial entropy citation needed apple who are known for implementing a facial recognition feature into the iphone attempts to protect users privacy with the secure enclave the mathematical structure of a user s face captured by the truedepth camera does not leave the user s device increasing the privacy and protection of personal information 12 13 however some concerns have been raised in regards to the level of security of the facial recognition on the devices for example there have been cases where family members were mistakenly recognized as their siblings 14 even with decentralized privacy protections a criticism of this approach is the inconvenience and cost to users of verifying strong identities and the risk of potential exclusion of users who do not readily have or cannot afford the requisite identity documents are reluctant to participate due to privacy and surveillance concerns or are wrongly excluded by errors in biometric tests 15 crypto biometrics edit crypto biometrics is an approach to resolving security concerns associated with biometric based human uniqueness verification 16 rather than storing sensitive data in centralized databases the method encrypts biometric information so that verification can occur without exposing the underlying data 17 the humanode project describes its implementation as combining confidential computing homomorphic encryption and zero knowledge proofs to verify biometric data within confidential virtual machines with the original biometric data remaining on the user s device 18 active implementations edit several protocols apply these techniques to decentralized human uniqueness verification world id developed by tools for humanity generates an iriscode from an iris scan conducted by a device called the orb then compares it against a blockchain registry using zero knowledge proofs via the open source semaphore protocol to confirm that the participant has not previously registered without linking verification events to any biometric data 19 the uniqueid protocol described in a 2018 paper by researchers at sharif university of technology combines biometric self attestation with peer verification through a dao governance structure where participants check for inconsistencies in other users submitted biometric claims 20 idena takes a non biometric approach participants confirm their humanity by solving ai resistant flip puzzles which are human authored image sequences requiring semantic rather than object recognition reasoning within a globally synchronous two minute window making it impractical for a single person to validate more than one account per session 21 demist relies on local peer verifications and democratic challenges to implement a sybil resistant network 22 challenges edit crypto biometric systems face unresolved questions about global scalability a 2026 survey of biometric enabled decentralized identity systems identified scalability and interoperability as major open problems noting that no standard protocol exists across systems and that their integration remains largely unexamined in the research literature 23 researchers have also raised concerns about whether facial biometrics provide sufficient statistical diversity at planetary scale as face matching accuracy degrades as population size grows and the probability of false positives increases 24 hardware requirements present a further barrier systems that depend on specialized capture devices may be unavailable or unaffordable in many regions 25 online turing tests edit another proposed class of approach extends the captcha principle of using turing tests to the unique human verification problem the idena network for example assigns participants to verify each other using flip tests 26 criticisms of this approach include the inconvenience to users of solving turing tests and whether artificial intelligence and deepfake technologies will soon be able to solve such tests automatically or convince real participants that a synthetic user is human during a verification interaction citation needed use cases edit one proposed use for proof of personhood is to ensure that voting power in permissionless consensus algorithms is widely distributed 6 and to avoid the re centralization that has been observed in proof of work mining pools 27 and predicted in proof of stake systems 28 another proposed use is to facilitate democratic governance in decentralized online systems including blockchains and cryptocurrencies that wish to enforce a one person one vote rule 29 see also edit proof of authority proof of space references edit douceur john r 2002 the sybil attack peer to peer systems lecture notes in computer science vol 2429 pp 251 60 doi 10 1007 3 540 45748 8_24 isbn 978 3 540 44179 3 what is captcha ibm www ibm com archived from the original on 2023 07 12 retrieved 2023 07 12 rodríguez c 2023 digital identity systems and human rights a legal framework for trust and security legal studies in the digital age retrieved march 12 2026 1 2 ford bryan strauss jacob 1 april 2008 an offline foundation for online accountable pseudonyms 1st workshop on social network systems socialnets 08 pp 31 6 doi 10 1145 1435497 1435503 isbn 978 1 60558 124 8 archived from the original on 30 october 2020 retrieved 28 october 2020 buterin vitalik 25 aug 2014 problems github archived from the original on 23 november 2020 retrieved 28 october 2020 1 2 3 maria borge eleftherios kokoris kogias philipp jovanovic linus gasser nicolas gailly bryan ford 29 april 2017 proof of personhood redemocratizing permissionless cryptocurrencies ieee security privacy on the blockchain ieee s b doi 10 1109 eurospw 2017 46 divya siddarth sergey ivliev santiago siri paula berman 13 oct 2020 who watches the watchmen a review of subjective approaches for sybil resistance in proof of personhood protocols arxiv 2008 05300 cs cr brenzikofer alain 14 january 2020 encointer an ecological egalitarian and private cryptocurrency and self sovereign identity system pdf github archived pdf from the original on 4 october 2021 retrieved 28 october 2020 gal shahaf ehud shapiro nimrod talmon october 2020 genuine personal identifiers and mutual sureties for sybil resilient community growth international conference on social informatics arxiv 1904 09630 doi 10 1007 978 3 030 60975 7_24 archived from the original on 2023 02 16 retrieved 2020 10 28 mohammad javad hajialikhani mohammad mahdi jahanara 20 june 2018 uniqueid decentralized proof of unique human arxiv 1806 07583 cs cr bimal viswanath ansley post krishna phani gummadi alan e mislove august 2010 an analysis of social network based sybil defenses acm sigcomm computer communication review 40 4 363 374 doi 10 1145 1851275 1851226 archived from the original on 2020 10 31 retrieved 2020 10 28 apple has a lot to say to al franken about face id on the iphone x mashable 2017 10 17 archived from the original on 2023 07 27 retrieved 2023 07 27 etherington darrell 2014 02 26 apple details touch id and the a7 s secure enclave in updated ios security document techcrunch archived from the original on 2023 07 27 retrieved 2023 07 27 times the brussels improved facial recognition on phones still not 100 secure say experts www brusselstimes com archived from the original on 2023 07 27 retrieved 2023 07 27 dixon pam 14 june 2017 a failure to do no harm india s aadhaar biometric id program and its inability to protect privacy in relation to measures in europe and the u s health and technology 7 4 539 567 doi 10 1007 s12553 017 0202 6 pmc 5741784 pmid 29308348 s2cid 8874699 lai junhao wang taotao zhang shengli yang qing liew soung chang 26 september 2024 biozero an efficient and privacy preserving decentralized biometric authentication protocol on open blockchain arxiv 2409 17509 cs cr yang wencheng wang song cui hui tang zhaohui li yan 2023 a review of homomorphic encryption for privacy preserving biometrics sensors 23 7 3566 bibcode 2023senso 23 3566y doi 10 3390 s23073566 pmc 10098691 pmid 37050625 kavazi dato smirnov victor shilina sasha 2024 humanode the first crypto biometric network proceedings of the 2024 6th blockchain and internet of things conference acm pp 143 150 doi 10 1145 3634814 3634843 plumb taryn 17 april 2026 world id expands its proof of human vision for the ai era computerworld retrieved 20 april 2026 hajialikhani mohammad javad jahanara mohammad mahdi 20 june 2018 uniqueid decentralized proof of unique human arxiv 1806 07583 cs cr idena proof of person technology idena documentation retrieved 20 april 2026 demist democracy now demist net retrieved 2026 09 21 rjab imen sliman layth 2026 survey on biometric authentication for decentralized identity management trends challenges and future directions future internet 18 3 126 doi 10 3390 fi18030126 lai junhao wang taotao zhang shengli yang qing liew soung chang 26 september 2024 biozero an efficient and privacy preserving decentralized biometric authentication protocol on open blockchain arxiv 2409 17509 cs cr plumb taryn 17 april 2026 world id expands its proof of human vision for the ai era computerworld retrieved 20 april 2026 idena how idena works archived from the original on 29 august 2021 retrieved 29 august 2021 vorick david 13 may 2018 the state of cryptocurrency mining archived from the original on 10 march 2020 retrieved 28 october 2020 giulia fanti leonid kogan sewoong oh kathleen ruan pramod viswanath gerui wang 18 february 2019 compounding of wealth in proof of stake cryptocurrencies pdf financial cryptography 2019 archived pdf from the original on 31 october 2020 retrieved 28 october 2020 ford bryan december 2020 technologizing democracy or democratizing technology a...