17.4. taler-auditor-offline(1)

17.4.1. Name

taler-auditor-offline - operations using the auditor’s private key

17.4.2. Synopsis

taler-auditor-offline [-c FILENAME | ––config=FILENAME] [-h | ––help] [-L LOGLEVEL | ––loglevel=LOGLEVEL] [-l FILENAME | ––logfile=FILENAME] [-v | ––version] [subcommand …]

17.4.3. Description

taler-auditor-offline is a command-line tool to be used by an auditor to sign that he is aware of certain keys being used by a exchange. Using this signature, the auditor affirms that he will verify that the exchange is properly accounting for coins of those denominations. The tool takes a list of subcommands as arguments which are then processed sequentially.

The tool includes two subcommands to interact online with the exchange’s REST APIs. The download subcommand downloads current public keys from the running exchange. Note that this only includes keys that the exchange operator has previously validated using the taler-exchange-offline tool. The resulting data serves as input to the sign and show subcommands.

The upload subcommand uploads the signatures created with the private key to the exchange. It handles the output of all subcommands (except download). The download and upload subcommands must naturally be run “online” and do not require access to the auditor’s private key, which should be kept offline.

All other subcommands are intended to be run “offline”. However, especially when testing, it is of course possible to run the subcommands online as well. Generally, subcommands read inputs (beyond command-line arguments) from stdin. However, they may also consume outputs of previous subcommands. The outputs of multiple subcommands are automatically combined, and if not consumed the final output is printed to stdout.

The general options for taler-auditor-offline are:

-c FILENAME | ––config=FILENAME
Use the configuration and other resources for the merchant to operate from FILENAME.
-h | ––help
Print short help on options.
-L LOGLEVEL | ––loglevel=LOGLEVEL
Specifies the log level to use. Accepted values are: DEBUG, INFO, WARNING, ERROR.
-l FILENAME | ––logfile=FILENAME
Send logging output to FILENAME.
-v | ––version
Print version information.

17.4.4. Configuration

The exchange and the taler-auditor-httpd must both be provided with the auditor’s public key, such that they can validate messages signed by the auditor. To obtain the auditor’s public key, use:

$ taler-auditor-offline setup

Note that if the private key file already exists, the above will simply output the existing key. Passing additional arguments after setup (including “-“) will cause the output to be encapsulated in JSON.

Relevant configuration options for taler-auditor-offline are:

  • [auditor/AUDITOR_PRIV_FILE] — where to store the private key

17.4.5. Subcommands

setup

When run the first time, this subcommand sets up the offline private key and outputs the resulting public key. Subsequent invocations will simply again output the (same) public key (in the format usable for the exchange configuration).

download

This subcommand must be run online. It downloads future signing and denomination keys with the associated meta data from the exchange and outputs the resulting JSON (for consumption by subsequent subcommands, or to stdout).

show

This subcommand outputs information about future signing and denomination keys for manual checking against the business-approved fee structure, lifetimes and other parameters.

It consumes the output of the download subcommand, either from stdin or directly.

Its output always goes to stdout for human consumption (not in JSON). It is usually a bad idea (but possible) to combine show with other subcommands, except maybe for testing.

sign

This subcommand signs information about future signing and denomination keys.

It consumes the output of the download subcommand, either from stdin or directly.

It outputs the signatures over all denomination and signing keys present in the input, in a format suitable for the upload subcommand.

upload

This subcommand uploads outputs from other subcommands (except download and show) to the exchange. Note that it is possible that some uploads succeed, while others fail, as the operation is not atomic.

The subcommand takes no arguments and has no output.

help

This subcommand shows a summary of all available subcommands with the required arguments.

17.4.6. Examples

Download public keys from an exchange (online)

$ taler-auditor-offline download > keys.json

Show information about public keys (offline or online)

$ taler-auditor-offline show < keys.json

Sign public keys (offline)

$ taler-auditor-offline sign < keys.json > sigs.json

Upload auditor signatures (online)

$ taler-auditor-offline upload < sigs.json

Download, sign and upload, all in one (online)

Note that doing this is only recommended in non-production deployments.

$ taler-auditor-offline download sign upload

17.4.7. Security considerations

The taler-auditor-offline tool assumes that it is run on a high-security system, especially for the sign subcommand.

The auditor should first use the show subcommand on the offline system to check that the keys being signed are acceptable. This process requires manual work: the auditor should check with the exchange operator that the keys (and meta data) matches that previously seen by the exchange operator when they used the taler-exchange-offline tool.

17.4.8. See Also

taler-auditor-exchange(1), taler-exchange-offline(1), taler.conf(5)

17.4.9. Bugs

Report bugs by using https://bugs.taler.net/ or by sending electronic mail to <taler@gnu.org>.