Gnutella, Freenet and Peer to Peer Networks By Norman Eng Steven Hnatko George Papadopoulos

Peer to Peer Fundamentals No dedicated servers or hierarchy among the computers All of the computers are equal Each computer functions as a client and a server with no administrator User on each computer decides what data on their computer will be shared on the network.

Gnutella and Freenet Freenet and Gnutella are two leading protocols for Peer to Peer networking They both create a decentralized network of computers, but do so with different implementations They handle and distribute data differently according to their own project goals

Freenet and Gnutella Freenet and Gnutella are two leading protocols for peer to peer networking Both create a decentralized network of computers, but do so with different implementations They handle and distribute data differently according to their own project goals Gnutella has a much broader user base than Freenet at this time, due to its easier implementation

Gnutella Basics Gnutella works by “viral propagation” Each node of the network simultaneously acts as a client and server, conducting searches while listening for incoming queries Gnutella defines these heterogeneous nodes as “servents”

Gnutella Basics (cont.) Properties of the Gnutella Network: Every node is equal Every node is both a server as well as a client Problems with the Gnutella Network: The Network cannot be described as a tree, because there is no hierarchy The Network can be cyclical, this causes excessive traffic

Standard Interactions Connecting to a Server(node) A node connecting to the network must first connect to a know node Client Says: GNUTELLA CONNECT Server Responds: GNUTELLA OK Downloading from a Server(node) HTTP Downloading Client Request String: GET /get/1234/bob.mp3 HTTP/1.0 Connection: Keep-Alive Server Response: HTTP 200 OK Server:Gnutella Content-type:application/binary Content-length:3289

Gnutella Descriptor Information Ping Used to actively discover hosts on the network Pong The response to a Ping Query The primary mechanism for searching the distributed network Query Hit The response to a Query Push/Get A mechanism that allows a “servent” to contribute/receive file-based data to the network

HTTP Message Format 3 Major Fields of Information: Initial line signaling Request/Response Headers (not mandatory) Additional Data (not mandatory)

Protocol To discover nodes, a servent will send out a Ping descriptor A servent receiving a Ping is expected to respond with a Pong and forward the Ping to all other nodes it is connected to, decreasing the TTL before forwarding Pongs may only be sent along the same path as the incoming Ping A search is propagated using a Query descriptor which is also routed to nodes and other nodes connected to them

Protocol Diagram 1) Incoming Ping 2) Outgoing Pong3) Routed Ping node Discovery

Protocol Diagram 1) File Transfer 1) Query2) QueryHit SearchTransfer

How Gnutella Retrieves Information

Freenet Overview Objectives of Freenet Protocol 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 function

Freenet Basics Network of equal nodes, each acting as client and server Information stored on hosts under searchable keys Total anonymity of users Owner of node has no knowledge of information in node’s datastore Data stored within nodes is encrypted

Freenet Interactions Connection to Freenet network Node connecting to network must obtain existing node’s address though out-of-band means Once connected, a new node message is propagated to randomly selected, connected nodes so existing nodes learn of new node’s existence

Freenet Interactions File Searches Node’s search string is hashed to key and own datastore checked on key If failure, key is sent to one connected node which searches it’s datastore and if fails, propagates search to one of it’s connected nodes, HTL decreased When file is found, search terminates and data is sent back to searching node, each node along path to searching node copies data to its own datastore as well

Freenet Searches

Freenet Details Datastore Key Types Keyword Signed Key (KSK) Content Hash Key (CHK) Most Common Name defined by data itself Signature Verified Key (SVK) Provide a “private” key for use with SSK SubSpace Key (SSK) Allow users to insert data “under” an SVK Can create hierarchical data structure under SVK

Freenet Details Common Message Header Information UniqueID: 64bit value assigned to generated message, used to prevent loops HopsToLive: Number of times a message may be forwarded before destroyed Depth: Distance in hops a message has traveled from its creator Source: Address identifying sender of message

Freenet Details Message Types HandshakeRequest Initiate connection to a node, ensures that node is connected and protocol versions match HandshakeReply Response to HandshakeRequest DataRequest Request from node for data transmission, must provide key for data as well

Freenet Details Message Types (cont) DataReply Reply of requested data, must provide data to be stored DataInsert Request from a node for data to be stored onto network, requesting node includes data and key RequestFailed Signals to sending node that data request failed

Major Differences Manner in which data is stored Level of Anonymity Developer’s Project Design Goals