1 / 6

Answer 1

Answer 1. no central points of attack. DHT algorithms are deterministic so if the file is on the network and the DHT is in a consistent state, it will be located .

olisa
Télécharger la présentation

Answer 1

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Answer 1 • no central points of attack. DHT algorithms are deterministic so if the file is on the network and the DHT is in a consistent state, it will be located. b) Gnutella is a distributed search protocol. It uses a flooding mechanism to propagate queries. File download is point to point between the query issuer and the node with the file. [2] Freenet is a distributed file stor- age system. It uses Peer ids and file keys to determine the best neighbour to route to and therefore does not employ flooding. Data travels back through the path that the query took. [2] Bittorrent is a decentralized download protocol. Upload bandwidth is shared between peers as they retrieve file segments from each other, thus reducing cost to the initial provider, and accellerating download speed. Bittorrentdows not address resource discovery but typically dedicated torrent websites are used to advertise files. [2]

  2. Answer 1 c) Bittorrentmakes use of hashing to ensure data integrity when downloading. Clients can verify downloaded chunks against the hashes defined in the .torrent file. Freenet uses file hashing to provide integrity checking of files through the Content Hash Key. Freenet also uses these hashes to evenly dis- tribute files across the network, much like a DHT. Gnutella does not employ file hashing because it is primarily a search protocol. Downloading is done via HTTP. Clients could support hashing by using the MD5 HTTP header which al- lows clients to verify the downloaded data against the header value provided by the server.

  3. Answer 1 d) Napster has a central point of attack due to its centralized dis- covery procedure, as was shown in the Napster court case. Gnutella on the other hand employs decentralzied discovery making it far harder to shut the system down. However, as Gnutella moved to a super-peer architecture, the network was found to be vulnerable to targeted attack on the super peers because if a super peer was taken down then many edge nodes connected to it would be cut off.Freenetis designed specifically to combat attack on the system and its users. When a File is propagated onto the network, the publisher does not know its whereabouts. Furthermore, all data is encrypted and files are broken up and spread across different parts of the network meaning that nodes storing the data can argue plausible deniability if accused of storing particular data.Nei- ther Napster nor Gnutella employ encryption to protect the data nor make any attempt to restrict access to users’ IP addresses, thus leaving their users exposed to attack.

  4. Answer 2 • statelessness - messages contain everything the server needs in order to fulfill the request. This eases the burden on the server because it doesn’t have to keep track of consecutive requests. Hypermedia as the engine of application state-state is perceived at the client side, not at the server side. Servers offer clients a series of potential next states to enter (via hyperlinks) and the client chooses a next state. But this transition is only perceived at the client side, not the server side. This again reduces the need for servers to track application state.

  5. Answer 2 b) Cookies are an example. Cookies are server generated identi- fiers for state. The client receives a Cookie in the HTTP headers from the server and reuses this in its own headers during further transactions. This allows the server to track the activities of the client, for example during the process of load- ing an online shopping cart. The process is not RESTful because the application state is stored at the server-side, not the client side. This in turn places greater burden on the server because it must ‘remember’ clients and ensure that it re- coups resources when a cookie session has come to an end.

  6. Answer 2 c) Collections of resources are exposed at an Atom server under a Service URL. The service URL contains a list of collections that each have a URL. To retrieve a particular resource, or Atom Entry, the Collection must be retrieved. This Collection contains the Atom Entries. To create a new resource in the collection, the client creates an Atom Entry and provides the content for that entry. It then uses the HTTP POST method to post the new Entry to the Collection URL. If all goes well, the server responds with an HTTP 201 Created message. This message contains an HTTP Location header that gives the URL of the newly created Entry on the server The client now has a way of accessing the new Entry. To retrieve the Entry, the client issues a HTTP GET request to the URL of the entry. The server responds with a 200 OK response with the Entry in the response. The client can now edit the Entry locally. To modify the published entry, the client issues a HTTP PUT request containing the modified Entry to the entry URL. If all goes well, the server responds with a 200 OK response. To delete an entry from a collection, the client can issue a HTTP DELETE request to the Entry URL. If all goes well, the server responds with a 200 OK response, having removed the Entry from the collection on the server side.

More Related