The paper "SybilGuard: Defending Against Sybil Attacks via Social Networks" by Haifeng Yu addresses the vulnerability of peer-to-peer and decentralized systems to sybil attacks, where malicious users create multiple fake identities to manipulate the system. The proposed protocol, SybilGuard, leverages social network structures to limit the impact of sybil attacks. The key idea is that malicious users can create many identities but few trust relationships, leading to a small "cut" in the graph between sybil and honest nodes. SybilGuard uses a decentralized approach based on social trust relationships to bound the number of sybil identities a malicious user can create. The protocol ensures that the number of attack edges (edges connecting sybil nodes to honest nodes) is limited by the number of trust relations between malicious and honest users. The effectiveness of SybilGuard is demonstrated both analytically and experimentally, showing that it can effectively bound the number and size of sybil groups, thus enhancing the security of decentralized systems against sybil attacks.The paper "SybilGuard: Defending Against Sybil Attacks via Social Networks" by Haifeng Yu addresses the vulnerability of peer-to-peer and decentralized systems to sybil attacks, where malicious users create multiple fake identities to manipulate the system. The proposed protocol, SybilGuard, leverages social network structures to limit the impact of sybil attacks. The key idea is that malicious users can create many identities but few trust relationships, leading to a small "cut" in the graph between sybil and honest nodes. SybilGuard uses a decentralized approach based on social trust relationships to bound the number of sybil identities a malicious user can create. The protocol ensures that the number of attack edges (edges connecting sybil nodes to honest nodes) is limited by the number of trust relations between malicious and honest users. The effectiveness of SybilGuard is demonstrated both analytically and experimentally, showing that it can effectively bound the number and size of sybil groups, thus enhancing the security of decentralized systems against sybil attacks.