# A P2P Scheme for Debating and Voting with Unconditional Flexibility
## 2 Preliminaries
### Physical Traceability  
In the first stage users must be identified to allow blind signatures. Users then participate in the second stage using an alias to protect their identity. Although blind signatures provide privacy at application layer, users can nevertheless be identified by correlating the transmission of the aliases with the IP addresses of the packets. This means that another tool for privacy is required at the network layer. This problem is solved by anonymous channels, that is, channels in which the sender of a message cannot be identified. Various proposals have been made for anonymizing channels:  
1. Network Address Translation (NAT) [35]: One defense consists of using the same IP address for multiple users, which is private and dynamic. A border router maintains the NAT tables, which must therefore be protected in order to maintain privacy.
2. Mixnets [6;7]: Mixnets are devices that receive a list of encrypted messages which are then shuffled and decrypted. Here, security depends on trusting in at least one node of the mixnet. Their shortcoming is that they cannot work until all the messages have been received, making it difficult to adapt to dynamic online debates.
3. DC-nets [36]: In a DC-net, users cooperate to behave as a virtual broadcast network. Every message is processed by all the users in the network. The problems in this case are twofold: scalability and the fact that one single user can block communications.
4. Public places: Public places, such as libraries, hotels, universities, Internet cafes, venues, etc., are points from which users can safely connect. Should an attacker manage to trace the IP address of an alias, this will show the public place, which cannot easily be related to a particular user, more so in the case of broadcast communications like Wi-Fi networks, for which authorities could offer access points.
5. Private proxies/VPN [37]: A proxy is an intermediary between users and the Internet. The connection with users can be protected by a VPN (encrypted channel), such that an attacker can follow the alias submissions to the proxy, but not beyond. This solution depends on the trustworthiness of the proxy. Even with this protection, however, statistical analysis over the network can correlate the times of outgoing alias submissions with user submissions entering the proxy. Nevertheless, this kind of attack is extremely difficult because the attacker must be able to manage most of the routers along the path (usually owned by different companies), and take advantage of low traffic conditions.
6. TOR network [38]: The idea behind TOR is to connect to a web server by tracing a route through a series of nodes. The user chooses the sequence of TOR nodes to follow from a list. Each node receives a request to send encrypted data to the following node, such that each one knows only the immediately previous and subsequent nodes, but cannot reveal the sequence, the sender or the destination. The higher the number of nodes the greater the latency, but also the better the security. TOR is constantly scrutinized and is vulnerable to statistical analysis, but is widely used as a secure privacy provider.
7. Invisible Internet Project (I2P) [39]: I2P provides a similar solution to TOR, but is more resistant to traffic analysis and incorporates different node sequences for incoming and outgoing packets, thus increasing security.  
Other solutions are available (e.g., Freenet, GNUnet, RetroShare), which can be combined (proxy with TOR) to increase security. Nevertheless, this question can be freely decided by the users as long as the e-voting scheme is properly designed.