ASCII Sequence Diagram Reference

Rules for drawing ASCII sequence diagrams inline in responses.

Column Layout

Lay out participants as column headers, each above a vertical | lifeline. Space columns ~28–32 characters apart so labels fit without wrapping:

Initiator                 Responder
   |                         |
   |                         |

For three or more participants, extend the layout rightward:

Client          Server          CA
   |               |             |
   |               |             |

Arrow Conventions

• Sending end: +
• Receiving end: > (rightward) or < (leftward)
• Solid lines --- for sends; dashed - - - for responses/replies
• Label goes on the arrow line, positioned between the two lifelines

   |                         |
   +------------------------>|  epk_I
   |                         |
   |  epk_R, Enc(k, cert_R)  |
   |<- - - - - - - - - - - - +
   |                         |

Self-Loops (Local Computation)

For operations that happen at a single party without sending a message:

   |                         |
   +--.                      |
   |  | Sign(sk, transcript) |
   |<-'                      |
   |                         |

Phase Labels

Group related steps under a phase label:

   |   -- Key Exchange --    |
   |                         |
   +------------------------>|  epk_I
   |                         |

Abort / Error Paths

Place abort paths after the main flow, separated by a blank line:

   |   [on auth failure]     |
   |  abort(AUTH_FAILED)     |
   |<- - - - - - - - - - - - +

Width and Labels

• Keep lines under ~60 characters wide
• If a label is too long, abbreviate it (e.g. Enc(k,id||σ)) and add a legend below the diagram explaining the abbreviations

Inline Output Format

Protocol: 
Output:   <filename>

            
   |                         |
   ...

## Protocol Summary

- **Parties:** ...
- **Round complexity:** ...
- **Key primitives:** ...
- **Authentication:** ...
- **Forward secrecy:** ...
- **Notable:** none