commit d04ab0477ae4feb9e038f99661b677f3d01c1289 Author: Iain R. Learmonth irl@fsfe.org Date: Mon Dec 8 15:45:21 2014 +0000

Initial import of taw TCP and UDP echo helpers --- test-helpers/th-004-raw-tcp-echo.md | 67 +++++++++++++++++++++++++++++++++++ test-helpers/th-005-raw-udp-echo.md | 54 ++++++++++++++++++++++++++++ 2 files changed, 121 insertions(+)

diff --git a/test-helpers/th-004-raw-tcp-echo.md b/test-helpers/th-004-raw-tcp-echo.md new file mode 100644 index 0000000..8b9cd54 --- /dev/null +++ b/test-helpers/th-004-raw-tcp-echo.md @@ -0,0 +1,67 @@ +# Specification version number + +2014-12-08-000 + +# Specification name + +Raw TCP Echo Test Helper + +# Helper description + +The Raw TCPEcho Test Helper listens on a TCP port for incoming connections. +When a connection is initiated, it accepts the connection, reads a dummy HTTP +request and sends an HTTP reply containing an encoding of the IP packets that +made up the TCP 3 way handshake [[Wikipedia-3WHS][]] which can be compared +against the packets sent by an ooniprobe test. + +# Helper preconditions + + * An Internet connection + * An Internet-Reachable TCP Port (preferably port 80) + * No known middleboxes rewriting IP or TCP headers in unexpected ways between + the helper and the transit ISP + +# Expected impact + +Ability to help an ooni-probe client determine if the IP or TCP headers have +been modified in transit, possibly indicating that the connection is being +transparently proxied. + +# Expected inputs + + * An HTTP 1.1 [[RFC2616][]] request that should not include any "dubious" Host: + header or keywords that might attract special treatment + +By emulating an HTTP session, a protocol known to censorship systems and +protocol-enhancing proxies, it will increase the chances to see intereference +occuring over using another protocol that may simply be passed through. + +# Expected output + + * An HTTP 1.1 [[RFC2616][]] reply that includes as its body an encoding of the + packets that made up the TCP 3 way handshake [[Wikipedia-3WHS][]] from the + vantage point of the helper + +The encoding chosen could be simply a binary PCAP trace, a base64 encoded PCAP +trace or even a JSON encoding of a dissector output as long as the dissector is +sufficiently verbose to maximise the usefulness of the helper. + +MIME types like text/html should be avoided as these have a stronger potential +for being rewritten on the wire. + +# Possible conclusions + +Possible conclusions that could be drawn from tests using this helper are: + + * The presence of a transparent proxy + * The presence of network address translation + * The bleaching of bits in the IP and TCP header by badly implemented middleboxes + +# Notes + +An implementation of this test helper is currently being worked on by Iain R. +Learmonth <irl@fsfe.org> using Scapy. + +[RFC2616]: http://tools.ietf.org/html/rfc2616 +[Wikipedia-3WHS]: http://en.wikipedia.org/wiki/Transmission_Control_Protocol#Connection_establ... + diff --git a/test-helpers/th-005-raw-udp-echo.md b/test-helpers/th-005-raw-udp-echo.md new file mode 100644 index 0000000..3414076 --- /dev/null +++ b/test-helpers/th-005-raw-udp-echo.md @@ -0,0 +1,54 @@ +# Specification version number + +2014-12-08-000 + +# Specification name + +Raw UDP Echo Test Helper + +# Helper description + +The Raw UDP Echo Test Helper listens on a UDP port for incoming packets. When a +packet is recieved, it sends a UDP packet in reply with the original packet's +header as its payload. + +# Helper preconditions + + * An Internet connection + * An Internet-Reachable UDP Port + * No known middleboxes rewriting UDP headers in unexpected ways between + the helper and the transit ISP + +# Expected impact + +Ability to help an ooni-probe client determine if the UDP header is being +rewritten and if packets are being truncated when UDP-lite is used with a +shorter checksum coverage than the full length of the packet using the UDP +protocol number in the IP header. + +# Expected inputs + + * A UDP packet addressed to the helper + * The destination port should not be one that might attract special treatment + * The payload should not contain keywords that might attract special treatment + +# Expected output + + * A UDP packet with the original incoming packet as its payload addressed to + return to the ooniprobe client + +# Possible conclusions + +Possible conclusions that could be drawn from tests using this helper are: + + * Middleboxes are truncating UDP-lite packets when the UDP protocol number is + used + * Middleboxes are discarding UDP-lite packets with the checksum does not match + for the full length of the packet + * Source and destination ports are being rewritten + +# Notes + +An implementation of this test helper is currently being worked on by Iain R. +Learmonth <irl@fsfe.org> using Scapy. +