Freenet: A Distributed Anonymous Information Storage and Retrieval System Ian Clarke, Oskar Sandberg, Brandon Wiley,Theodore W. Hong Presented by Zhengxiang Pan Jan. 30

Design Goals Anonymity for both producers and consumers of information Deniability for storers of information Resistance to attempts by third parties to deny access to information Efficient dynamic storage and routing of information Decentralization of all network functions

Architecture -overview A cooperative distributed file system Location independence Transparent lazy replication Local datastore & dynamic routing table No privilege No hierarchy No central point

Architecture – Keys and Searching KSK: keyword-signed key KSK: keyword-signed key Easy to remember Easy to remember Problematic flat global namespace Problematic flat global namespace SSK: signed-subspace key SSK: signed-subspace key Personal namespace Personal namespace Manage directory Manage directory CHK: content-hash key CHK: content-hash key Pseudo-unique file key Pseudo-unique file key Useful for updating and splitting Useful for updating and splitting

Architecture – Retrieving data

Architecture – Storing data Calculate file key Calculate file key Send insert message like request Send insert message like request If “ all clear ” send the data to insert If “ all clear ” send the data to insert Stored in each node alone the path Stored in each node alone the path Each node add entry to routing table associating the key and the data source (can be random decided) Each node add entry to routing table associating the key and the data source (can be random decided)

Architecture – others Managing data Managing data LRU: Least Recently Used Cache LRU: Least Recently Used Cache Routing table entries: in same fashion but will be kept longer Routing table entries: in same fashion but will be kept longer Encrypted contents Encrypted contents Adding nodes Adding nodes Find existing nodes by out-of-band means Find existing nodes by out-of-band means New-node announcement New-node announcement Consistent random key for new node in routing table Consistent random key for new node in routing table

Protocol details Flexible in transport mechanism Flexible in transport mechanism Node address e.g. tcp/ :19114 Node address e.g. tcp/ : bit transaction ID 64-bit transaction ID Hops-to-live & depth Hops-to-live & depth

Performance analysis -convergence Time evolution of the request pathlength

Performance analysis -scalability Request pathlength VS network size

Performance analysis – fault tolerance Change in request pathlength under network failure

Performance analysis – small world model Distribution of link number among Freenet nodes

Security Anonymity of requestors and inserters Anonymity of requestors and inserters Key anonymity: vulnerable to dictionary attack Key anonymity: vulnerable to dictionary attack Sender anonymity: local eavesdrop Sender anonymity: local eavesdrop Anonymity of storer: encrypted contents Anonymity of storer: encrypted contents Malicious modification: keys Malicious modification: keys Denial-of-service: a large number of junk files Denial-of-service: a large number of junk files

More ? More ?