About these specifications
Introduction
1.
A short introduction to Tor
1.1.
Notation and conventions
The core Tor protocol
2.
Tor Protocol Specification
2.1.
Preliminaries
2.2.
Relay keys and identities
2.3.
Channels
2.3.1.
Negotiating and initializing channels
2.3.1.1.
Obsolete channel negotiation handshakes
2.3.2.
Cells (messages on channels)
2.4.
Circuit management
2.4.1.
CREATE and CREATED cells
2.4.2.
Setting circuit keys
2.4.3.
Creating circuits
2.4.4.
Tearing down circuits
2.4.5.
Routing relay cells
2.4.6.
Handling relay_early cells
2.5.
Application connections and stream management
2.5.1.
Relay cells
2.5.2.
Opening streams and transferring data
2.5.3.
Closing streams
2.5.4.
Remote hostname lookup
2.6.
Flow control
2.7.
Subprotocol versioning
2.8.
Certificates in Tor
3.
Tor directory protocol, version 3
3.1.
Outline
3.2.
netdoc document meta-format
3.3.
Router operation and formats
3.3.1.
Uploading server descriptors and extra-info documents
3.3.1.1.
Server descriptor format
3.3.1.2.
Extra-info document format
3.3.1.3.
Nonterminals in server descriptors
3.4.
Directory authority operation and formats
3.4.1.
Creating key certificates
3.4.2.
Accepting server descriptor and extra-info document uploads
3.4.3.
Computing microdescriptors
3.4.4.
Exchanging votes
3.4.4.1.
Vote and consensus status document formats
3.4.4.2.
Assigning flags in a vote
3.4.4.3.
Serving bandwidth list files
3.4.5.
Downloading information from other directory authorities
3.4.6.
Computing a consensus from a set of votes
3.4.7.
Exchanging detached signatures
3.4.8.
Publishing the signed consensus
3.5.
Directory cache operation
3.6.
Client operation
3.7.
Standards compliance
3.8.
Consensus-negotiation timeline.
3.9.
General-use HTTP URLs
3.10.
Converting a curve25519 public key to an ed25519 public key
3.11.
Inferring missing proto lines.
3.12.
Limited ed diff format
3.13.
Tor Shared Random Subsystem Specification
3.13.1.
Introduction
3.13.2.
Overview
3.13.3.
Protocol
3.13.4.
Specification [SPEC]
3.13.5.
Security Analysis
3.13.6.
Discussion
3.13.7.
Acknowledgements
4.
Tor Path Specification
4.1.
General operation
4.2.
Building circuits
4.2.1.
When we build
4.2.2.
Path selection and constraints
4.2.3.
Cannibalizing circuits
4.2.4.
Learning when to give up ("timeout") on circuit construction
4.2.5.
Handling failure
4.3.
Attaching streams to circuits
4.4.
Hidden-service related circuits
4.5.
Guard nodes
4.6.
Server descriptor purposes
4.7.
Detecting route manipulation by Guard nodes (Path Bias)
5.
Tor Guard Specification
5.1.
State instances
5.2.
Circuit Creation, Entry Guard Selection (1000 foot view)
5.3.
The algorithm.
5.4.
Appendices
6.
Tor Vanguards Specification
6.1.
Full Vanguards
6.2.
Vanguards-Lite
6.3.
Path Construction
6.4.
Statistical Analysis
7.
Tor Padding Specification
7.1.
Overview
7.2.
Connection-level padding
7.3.
Circuit-level padding
7.4.
Acknowledgments
8.
Preventing Denial-Of-Service
8.1.
Overview
8.2.
Memory exhaustion
Additional behaviors for clients
9.
Tor's extensions to the SOCKS protocol
10.
Special Hostnames in Tor
Onion services
11.
Tor Rendezvous Specification - Version 3
11.1.
Hidden services: overview and preliminaries.
11.2.
Protocol overview
11.3.
Generating and publishing hidden service descriptors [HSDIR]
11.3.1.
Deriving blinded keys and subcredentials [SUBCRED]
11.3.2.
Publishing shared random values [PUB-SHAREDRANDOM]
11.3.3.
Hidden service descriptors: outer wrapper [DESC-OUTER]
11.3.4.
Hidden service descriptors: encryption format [HS-DESC-ENC]
11.4.
The introduction protocol [INTRO-PROTOCOL]
11.5.
The rendezvous protocol
11.6.
Encrypting data between client and host
11.7.
Encoding onion addresses [ONIONADDRESS]
11.8.
Managing streams
11.9.
References
11.10.
Appendix A: Signature scheme with key blinding [KEYBLIND]
11.11.
Appendix B: Selecting nodes [PICKNODES]
11.12.
Appendix C: Recommendations for searching for vanity .onions [VANITY]
11.13.
Appendix D: (removed)
11.14.
Appendix E: Reserved numbers
11.15.
Appendix F: Hidden service directory format [HIDSERVDIR-FORMAT]
11.16.
Appendix G: Managing restricted discovery data [RESTRICTED-DISCOVERY-MGMT]
11.17.
Appendix F: Two methods for managing revision counters.
11.18.
Appendix G: Test vectors
12.
Proof of Work for onion service introduction
12.1.
Motivation
12.2.
Common protocol
12.3.
Version 1, Equi-X and Blake2b
12.4.
Analysis and discussion
Anticensorship tools and protocols
13.
BridgeDB specification
14.
Extended ORPort for pluggable transports
15.
Pluggable Transport Specification (Version 1)
15.1.
Introduction
15.2.
Architecture Overview
15.3.
Specification
15.3.1.
Pluggable Transport Naming
15.3.2.
Pluggable Transport Configuration Environment Variables
15.3.3.
Pluggable Transport To Parent Process Communication
15.3.4.
Pluggable Transport Shutdown
15.3.5.
Pluggable Transport Client Per-Connection Arguments
15.4.
Anonymity Considerations
15.5.
References
15.6.
Acknowledgments
15.7.
Appendix A: Example Client Pluggable Transport Session
15.8.
Appendix B: Example Server Pluggable Transport Session
For C Tor only
16.
The Tor Control Protocol
16.1.
Protocol outline
16.2.
Message format
16.3.
Commands
16.4.
Replies
16.5.
Implementation notes
17.
How Tor Version Numbers Work
Less commonly needed file formats
18.
Tor Bandwidth File Format
18.1.
Scope and preliminaries
18.2.
Format details
18.2.1.
Definitions
18.2.2.
Header List format
18.2.3.
Relay Line format
18.2.4.
Implementation details
18.3.
Sample data
18.4.
Scaling bandwidths
Implementation details
19.
Tor Directory List Format
Reserved names and numbers
20.
Tor network parameters
21.
SSH protocol extensions
Unfinished
22.
Glossary
Historical information
23.
Historical protocol elements and behaviours
23.1.
Historical netdoc Items
Maintenance and and editing of the Tor Specifications
24.
About the Tor Specifications documents
25.
Style guide
26.
Permalinks
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Tor Specifications
Circuit management
This section describes how circuits are created, and how they operate once they are constructed.