[Osiris]

Retroshare is a secure Instant Messenger with File Sharing options. It uses a 2048-bit RSA encryption keys in combination with trust style authentication to ensure maximum security. Connections are only established to friends who received your Retroshare certificate which is of course a little bit more complicated but it is well worth it.
Once the certificate has been added your friend is verified and it’s possible to chat, group chat and share files with them. Everything is encrypted using 2048-bit RSA keys which means that it is not possible for your Internet Provider or someone else to snoop on the data that is send and received.
Turtle Hopping, also known as Turtle F2F, is being used to download files from users that are not in your friends list. This is done by creating a link between your computer, one of your friends, one of this friends and so on until the computer is reached that is offering the file.
The advantage of this method is of course, that the one offering the file is not seeing your IP address but only that of his friend who is downloading the data and sending it in the reverse direction. In short: You never know any IP address other than the IP of your friends. The encrypted traffic means that no one from outside is able to snoop on the traffic.
If someone would sit in the middle he would either be your friend or a friend of a friend. The first case would mean that he would know your IP address because he is someone that you send your certificate to. The second case would mean that he does not know your IP address because there is at least one node between your computer and his.
There are a few drawbacks though. It is rather complicated to exchange the certificates. They have to be saved to disk and send by email, ftp or burned on a media. Many users do not want to go this extra mile even if it would mean increased security.
The second and probably bigger drawback is the fact that many users have to download a file so that you can download it. If four nodes are between your computer and the computer that offers the file that you download it would mean that five users would have to download that file. (the four nodes and of course you) This could take a very long time if the file is a large one.
Read More:
Retroshare available for Linux and Windows