mirror of
https://github.com/trezor/trezor-firmware.git
synced 2024-11-27 01:48:17 +00:00
130 lines
4.6 KiB
Markdown
130 lines
4.6 KiB
Markdown
# Sessions
|
|
|
|
Trezor has limited support for logical sessions. The main purpose is to enable seamless
|
|
operation with multiple passphrases.
|
|
|
|
**Warning: Session isolation does not exist.** Host software is responsible for
|
|
maintaining isolation. Running multiple host-side applications at the same time is not
|
|
recommended.
|
|
|
|
See "Caveats" section below for details.
|
|
|
|
Support for isolated sessions is in the works, see
|
|
[#79](https://github.com/trezor/trezor-firmware/issues/79).
|
|
|
|
## Session lifecycle
|
|
|
|
After Trezor starts up, no session exists. Any attempt to use session data (i.e., the
|
|
seed) will be rejected with `InvalidSession` error code.
|
|
|
|
New session is started by calling `Initialize` with no arguments. The response is a
|
|
`Features` message, which contains a 32-byte `session_id`. All subsequent commands
|
|
happen within the given session.
|
|
|
|
To resume a previous session (after creating a new one), call `Initialize` with a stored
|
|
`session_id` as an argument.
|
|
|
|
Attempt to resume an unknown session ID will transparently allocate a new session ID.
|
|
|
|
Since firmwares 1.9.4 / 2.3.4, it is possible to destroy the current session via the
|
|
`EndSession` call. The session and all its associated data is wiped from Trezor memory,
|
|
and it is impossible to resume the session. Trezor returns to the initial state and
|
|
all requests will return `InvalidSession`.
|
|
|
|
There is no explicit way to leave a session and keep its data for later resumption.
|
|
Instead, you can switch to a new session via `Initialize` with no arguments.
|
|
|
|
At the moment, both T1 and TT allow for 10 sessions to exist at the same time. When a
|
|
new session needs to be allocated and there is no space in the cache, the least recently
|
|
used session is evicted.
|
|
|
|
Sessions only exist in RAM and are lost when Trezor is disconnected.
|
|
|
|
All commands are performed in the context of the current session, until one of the
|
|
following happens:
|
|
|
|
* Host calls `EndSession`. The current session is destroyed and Trezor returns to the
|
|
initial state.
|
|
* Host calls `Initialize` with no arguments, or with an unknown `session_id`. A new
|
|
session is allocated and its id returned in the `Features` message.
|
|
* Host calls `Initialize` with a known `session_id`. The specified session is resumed
|
|
and its `session_id` is returned in the `Features` message.
|
|
* Trezor is disconnected.
|
|
|
|
## Caveats
|
|
|
|
* Sessions only exist on the protobuf message level. **There is no proper isolation.**
|
|
Multiple host applications can insert commands into each other's sessions.
|
|
|
|
It is recommended to send `Initialize` to resume a session immediately before each
|
|
flow. However, even this does not guarantee that another application doesn't insert
|
|
its own `Initialize` in the time it takes you to send the next command.
|
|
|
|
The reverse is also true: session management does not prevent other applications from
|
|
inserting commands under the currently active session (and therefore passphrase),
|
|
without knowledge of the session ID or the passphrase.
|
|
|
|
* It is impossible to run complex flows concurrently. If an application is in the middle
|
|
of Bitcoin signing, sending `Initialize` will cancel the signing flow. Resuming the
|
|
appropriate session later will _not_ continue where it left off.
|
|
|
|
## Examples
|
|
|
|
Allocate a new session, perform a command, and end the session:
|
|
```
|
|
Initialize()
|
|
---------> Features(..., session_id=AAAA)
|
|
<---------
|
|
---<now in session AAAA>---
|
|
Request
|
|
---------> Response
|
|
<---------
|
|
EndSession()
|
|
---------> Success()
|
|
<---------
|
|
---<now in no session>---
|
|
```
|
|
|
|
Allocate two new sessions, resume the first one later:
|
|
```
|
|
Initialize()
|
|
---------> Features(..., session_id=AAAA)
|
|
<---------
|
|
---<now in session AAAA>---
|
|
Request
|
|
---------> Response
|
|
<---------
|
|
|
|
Initialize()
|
|
---------> Features(..., session_id=BBBB)
|
|
<---------
|
|
---<now in session BBBB>---
|
|
Request
|
|
---------> Response
|
|
<---------
|
|
|
|
Initialize(session_id=AAAA)
|
|
---------> Features(..., session_id=AAAA)
|
|
<---------
|
|
---<now in session AAAA>---
|
|
Request
|
|
---------> Response
|
|
<---------
|
|
```
|
|
|
|
Attempt to resume session that is not in the cache:
|
|
```
|
|
Initialize()
|
|
---------> Features(..., session_id=AAAA)
|
|
<---------
|
|
---<now in session AAAA>---
|
|
EndSession()
|
|
---------> Success()
|
|
<---------
|
|
---<now in no session>---
|
|
Initialize(session_id=AAAA)
|
|
---------> Features(..., session_id=BBBB)
|
|
<---------
|
|
---<now in session BBBB>---
|
|
```
|