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diff --git a/curvetun.8 b/curvetun.8 new file mode 100644 index 0000000..37208b4 --- /dev/null +++ b/curvetun.8 @@ -0,0 +1,196 @@ +.\" netsniff-ng - the packet sniffing beast +.\" Copyright 2013 Daniel Borkmann. +.\" Subject to the GPL, version 2. + +.TH CURVETUN 8 "03 March 2013" "Linux" "netsniff-ng toolkit" +.SH NAME +curvetun \- a lightweight Curve25519 IP tunnel + +.SH SYNOPSIS + +\fB curvetun\fR [\fIoptions\fR] + +.SH DESCRIPTION +curvetun is a lightweight, high-speed ECDH multiuser IP tunnel for Linux +that is based on epoll(2). curvetun uses the Linux TUN/TAP interface and +supports {IPv4, IPv6} over {IPv4, IPv6} with UDP or TCP as carrier protocols. + +It has an integrated packet forwarding trie, thus multiple users with +different IPs can be handled via a single tunnel device on the server side +and flows are scheduled for processing in a CPU affine way, at least in case +of TCP as a carrier protocol. + +As key management, public-key cryptography based on elliptic curves are being +used and packets are encrypted end-to-end by the symmetric stream cipher +Salsa20 and authenticated by the MAC Poly1305, where keys have previously +been computed with the ECDH key agreement protocol Curve25519. + +Cryptography is based on Daniel J. Bernstein's networking and cryptography +library ``NaCl''. By design, curvetun does not provide any particular pattern +or default port numbers that gives certainty that the connection from a +particular flow is actually running curvetun. + +However, if you have further needs to bypass censorship, you can try using +curvetun in combination with Tor's obfsproxy or Telex. Furthermore, curvetun +also protects you against replay attacks and DH man in the middle. +Additionally, server-side syslog event logging can also be disabled to not +reveal any critical user connection data. + +.IP " 1." 4 +obfsproxy from the TOR project +.RS 4 +\%https://www.torproject.org/projects/obfsproxy.html.en +.RE + +.IP " 2." 4 +Telex, anticensorship in the network infrastructure +.RS 4 +\%https://telex.cc/ +.RE + +.SH OPTIONS + +todo + +.SH CRYPTOGRAPHY +IP tunnels are usually used to create virtual private networks (VPN), where +parts of the network can only be reached via an unsecure or untrusted underlay +network like the Internet. Only few software exists to create such tunnels, +or, VPNs. Two popular representatives of such software are OpenVPN and VTUN. + +The latter also introduced the TUN/TAP interfaces into the Linux kernel. VTUN +only has a rather basic encryption module, that doesn't fit into todays +cryptographic needs. By default MD5 is used to create 128-Bit wide keys for +the symmetric BlowFish cipher in ECB mode [1]. + +Although OpenSSL is used in both, VTUN and OpenVPN, OpenVPN is much more +feature rich regarding ciphers and user authentication. Nevertheless, letting +people choose ciphers or authentication methods does not necessarily mean a +good thing: administrators could either prefer speed over security and +therefore choose weak ciphers, so that the communication system will be as +good as without any cipher; they could choose weak passwords for symmetric +encryption or they could misconfigure the communication system by having too +much choices of ciphers and too little experience for picking the right one. + +Next to the administration issues, there are also software development issues. +Cryptographic libraries like OpenSSL are a huge mess and too low-level and +complex to probably fully understand or correctly apply, so that they form a +further ground for vulnerabilities of such software. + +In 2010, the cryptographers Tanja Lange and Daniel J. Bernstein have therefore +created and published a cryptography library for networking, which is called +NaCl (pronounced ``salt''). NaCl challenges such addressed problems as in +OpenSSL and, in contrast to the rather generic use of OpenSSL, was created +with a strong focus on public-key authenticated encryption based on elliptic +curve cryptography, which is used in curvetun. Partially quoting Daniel J. +Bernstein: + +RSA is somewhat older than elliptic-curve cryptography: RSA was introduced +in 1977, while elliptic-curve cryptography was introduced in 1985. However, +RSA has shown many more weaknesses than elliptic-curve cryptography. RSA's +effective security level was dramatically reduced by the linear sieve in the +late 1970s, by the quadratic sieve and ECM in the 1980s, and by the +number-field sieve in the 1990s. For comparison, a few attacks have been +developed against some rare elliptic curves having special algebraic +structures, and the amount of computer power available to attackers has +predictably increased, but typical elliptic curves require just as much +computer power to break today as they required twenty years ago. + +IEEE P1363 standardized elliptic-curve cryptography in the late 1990s, +including a stringent list of security criteria for elliptic curves. NIST +used the IEEE P1363 criteria to select fifteen specific elliptic curves at +five different security levels. In 2005, NSA issued a new ``Suite B'' +standard, recommending the NIST elliptic curves (at two specific security +levels) for all public-key cryptography and withdrawing previous +recommendations of RSA. + +curvetun uses a particular elliptic curve, Curve25519, introduced in the +following paper: Daniel J. Bernstein, ``Curve25519: new Diffie-Hellman speed +records,'' pages 207-228 in Proceedings of PKC 2006, edited by Moti Yung, +Yevgeniy Dodis, Aggelos Kiayias, and Tal Malkin, Lecture Notes in Computer +Science 3958, Springer, 2006, ISBN 3-540-33851-9. + +This elliptic curve follows all of the standard IEEE P1363 security criteria. +It also follows new recommendations that achieve ``side-channel immunity'' +and ``twist security'' while improving speed. What this means is that secure +implementations of Curve25519 are considerably simpler and faster than secure +implementations of (e.g.) NIST P-256; there are fewer opportunities for +implementors to make mistakes that compromise security, and mistakes are +more easily caught by reviewers. + +An attacker who spends a billion dollars on special-purpose chips to attack +Curve25519, using the best attacks available today, has about 1 chance in +1000000000000000000000000000 of breaking Curve25519 after a year of computation. +One could achieve similar levels of security with 3000-bit RSA, but +encryption and authentication with 3000-bit RSA are not nearly fast enough +to handle tunnel traffic and would require much more space in network +packets. + +.IP " 1." 4 +Security analysis of VTun +.RS 4 +\%http://www.off.net/~jme/vtun_secu.html +.RE + +.IP " 2." 4 +NaCl: Networking and Cryptography library +.RS 4 +\%http://nacl.cr.yp.to/ +.RE + +.SH SETUP EXAMPLE +If you've never run curvetun before, you need to do an initial setup once. + +At first, make sure that the servers and clients clocks are periodically +synced, for instance, by running a ntp daemon. This is necessary to protect +against replay attacks. Also, make sure if you have read and write access to +/dev/net/tun. You should not run curvetun as root! Then, after you assured +this, the first step is to generate keys and config files. On both, the client +and server do: + +.B curvetun -k + +You are asked for a username. You can use an email address or whatever suits +you. Here, we assume, you've entered 'mysrv1' on the server and 'myclient1' +on the client side. + +Now, all necessary file have been created under ~/.curvetun. Files include +``priv.key'', ``pub.key'', ``username', ``clients'' and ``servers''. + +``clients'' and ``servers'' are empty at the beginning and need to be filled. +The ``clients'' file is meant for the server, so that it knows what clients +are allowed to connect. The ``servers'' file is for the client, where it can +select curvetun servers to connect to. Both files are kept very simple, so that +a single configuration line per client or server is sufficient. + +The client needs to export it's public key data for the server: + +.B curvetun -x + +todo + +.SH NOTE +This software is an experimental prototype intended for researchers. Likely, +it will mature over time, but it is currently not advised using this software +when life is put at risk. + +.SH LEGAL +curvetun is licensed under the GNU GPL version 2.0. + +.SH HISTORY +.B curvetun +was originally written for the netsniff-ng toolkit by Daniel Borkmann. It is +currently maintained by Tobias Klauser <tklauser@distanz.ch> and Daniel +Borkmann <dborkma@tik.ee.ethz.ch>. + +.SH SEE ALSO +.BR netsniff-ng (8), +.BR trafgen (8), +.BR mausezahn (8), +.BR bpfc (8), +.BR ifpps (8), +.BR flowtop (8), +.BR astraceroute (8) + +.SH AUTHOR +Manpage was written by Daniel Borkmann. |