Tor’s modules
Generic modules
buffers.c
- Implements the
buf_t
buffered data type for connections, and several low-level data handling functions to handle network protocols on it.
channel.c
- Generic channel implementation. Channels handle sending and receiving cells among tor nodes.
channeltls.c
- Channel implementation for TLS-based OR connections. Uses
connection_or.c
.
circuitbuild.c
- Code for constructing circuits and choosing their paths. (Note: this module could plausibly be split into handling the client side, the server side, and the path generation aspects of circuit building.)
circuitlist.c
- Code for maintaining and navigating the global list of circuits.
circuitmux.c
- Generic circuitmux implementation. A circuitmux handles deciding, for a particular channel, which circuit should write next.
circuitmux_ewma.c
- A circuitmux implementation based on the EWMA (exponentially weighted moving average) algorithm.
circuituse.c
- Code to actually send and receive data on circuits.
command.c
- Handles incoming cells on channels.
config.c
- Parses options from torrc, and uses them to configure the rest of Tor.
confparse.c
- Generic torrc-style parser. Used to parse torrc and state files.
connection.c
- Generic and common connection tools, and implementation for the simpler connection types.
connection_edge.c
- Implementation for entry and exit connections.
connection_or.c
- Implementation for OR connections (the ones that send cells over TLS).
main.c
- Principal entry point, main loops, scheduled events, and network management for Tor.
ntmain.c
- Implements Tor as a Windows service. (Not very well.)
onion.c
- Generic code for generating and responding to CREATE and CREATED cells, and performing the appropriate onion handshakes. Also contains code to manage the server-side onion queue.
onion_fast.c
- Implements the old SHA1-based CREATE_FAST/CREATED_FAST circuit creation handshake. (Now deprecated.)
onion_ntor.c
- Implements the Curve25519-based NTOR circuit creation handshake.
onion_tap.c
- Implements the old RSA1024/DH1024-based TAP circuit creation handshake. (Now deprecated.)
relay.c
- Handles particular types of relay cells, and provides code to receive, encrypt, route, and interpret relay cells.
scheduler.c
- Decides which channel/circuit pair is ready to receive the next cell.
statefile.c
- Handles loading and storing Tor’s state file.
tor_main.c
- Contains the actual
main()
function. (This is placed in a separate file so that the unit tests can have their own main()
.)
Node-status modules
directory.c
- Implements the HTTP-based directory protocol, including sending, receiving, and handling most request types. (Note: The client parts of this, and the generic-HTTP parts of this, could plausibly be split off.)
microdesc.c
- Implements the compact “microdescriptor” format for keeping track of what we know about a router.
networkstatus.c
- Code for fetching, storing, and interpreting consensus vote documents.
nodelist.c
- Higher-level view of our knowledge of which Tor servers exist. Each
node_t
corresponds to a router we know about.
routerlist.c
- Code for storing and retrieving router descriptors and extrainfo documents.
routerparse.c
- Generic and specific code for parsing all Tor directory information types.
routerset.c
- Parses and interprets a specification for a set of routers (by IP range, fingerprint, nickname (deprecated), or country).
Client modules
addressmap.c
- Handles client-side associations between one address and another. These are used to implement client-side DNS caching (NOT RECOMMENDED), MapAddress directives, Automapping, and more.
circpathbias.c
- Path bias attack detection for circuits: tracks whether connections made through a particular guard have an unusually high failure rate.
circuitstats.c
- Code to track circuit performance statistics in order to adapt our behavior. Notably includes an algorithm to track circuit build times.
dnsserv.c
- Implements DNSPort for clients. (Note that in spite of the word “server” in this module’s name, it is used for Tor clients. It implements a DNS server, not DNS for servers.)
entrynodes.c
- Chooses, monitors, and remembers guard nodes. Also contains some bridge-related code.
torcert.c
- Code to interpret and generate Ed25519-based certificates.
Server modules
dns.c
- Server-side DNS code. Handles sending and receiving DNS requests on exit nodes, and implements the server-side DNS cache.
dirserv.c
- Implements part of directory caches that handles responding to client requests.
ext_orport.c
- Implements the extended ORPort protocol for communication between server-side pluggable transports and Tor servers.
hibernate.c
- Performs bandwidth accounting, and puts Tor relays into hibernation when their bandwidth is exhausted.
router.c
- Management code for running a Tor server. In charge of RSA key maintenance, descriptor generation and uploading.
routerkeys.c
- Key handling code for a Tor server. (Currently handles only the Ed25519 keys, but the RSA keys could be moved here too.)
Onion service modules
rendcache.c
- Stores onion service descriptors.
rendclient.c
- Client-side implementation of the onion service protocol.
rendcommon.c
- Parts of the onion service protocol that are shared by clients, services, and/or Tor servers.
rendmid.c
- Tor-server-side implementation of the onion service protocol. (Handles acting as an introduction point or a rendezvous point.)
rendservice.c
- Service-side implementation of the onion service protocol.
replaycache.c
- Backend to check introduce2 requests for replay attempts.
Authority modules
dircollate.c
- Helper for
dirvote.c
: Given a set of votes, each containing a list of Tor nodes, determines which entries across all the votes correspond to the same nodes, and yields them in a useful order.
dirvote.c
- Implements the directory voting algorithms that authorities use.
keypin.c
- Implements a persistent key-pinning mechanism to tie RSA1024 identities to ed25519 identities.
Miscellaneous modules
control.c
- Implements the Tor controller protocol.
cpuworker.c
- Implements the inner work queue function. We use this to move the work of circuit creation (on server-side) to other CPUs.
fp_pair.c
- Types for handling 2-tuples of 20-byte fingerprints.
geoip.c
- Parses geoip files (which map IP addresses to country codes), and performs lookups on the internal geoip table. Also stores some geoip-related statistics.
policies.c
- Parses and implements Tor exit policies.
reasons.c
- Maps internal reason-codes to human-readable strings.
rephist.c
- Tracks Tor servers’ performance over time.
status.c
- Writes periodic “heartbeat” status messages about the state of the Tor process.
transports.c
- Implements management for the pluggable transports subsystem.