KSI Signature Provider (rsyslog-ksi-ls12)

Module Name: rsyslog-ksi-ls12

Available Since: 8.27

Author: Guardtime & Adiscon


The rsyslog-ksi-ls12 module enables record level log signing with Guardtime KSI Blockchain. KSI signatures provide long-term log integrity and prove the time of log records cryptographically using independent verification.

Main features of the rsyslog-ksi-ls12 module are:

  • Automated online signing of file output log.

  • Efficient block-based signing with record-level verification.

  • Log records removal detection.

For best results use the rsyslog-ksi-ls12 module together with Guardtime logksi tool, which will become handy in:

  • Signing recovery.

  • Extension of KSI signatures inside the log signature file.

  • Verification of the log using log signatures.

  • Extraction of record-level signatures.

  • Integration of log signature files (necessary when signing in async mode).

Getting Started

To get started with log signing:

The format of the output depends on signing mode enabled (synchronous (sync) or asynchronous (async)).

  • In sync mode, log signature file is written directly into file <logfile>.logsig. This mode is blocking as issuing KSI signatures one at a time will halt actual writing of log lines into log files. This mode suits for a system where signatures are issued rarely and delay caused by signing process is acceptable. Advantage compared to async mode is that the user has no need to integrate intermediate files to get actual log signature.

  • In async mode, log signature intermediate files are written into directory <logfile>.logsig.parts. This mode is not blocking enabling high availability and concurrent signing of several blocks at the same time. Log signature is divided into two files, where one contains info about log records and blocks, and the other contains KSI signatures issued asynchronously. To create <logfile>.logsig from <logfile>.logsig.parts, use logksi integrate <logfile>. Advantage compared to sync mode is much better operational stability and speed.

Currently the log signing is only supported by the file output module, thus the action type must be omfile. To activate signing, add the following parameters to the action of interest in your rsyslog configuration file:

Mandatory parameters (no default value defined):

  • sig.provider specifies the signature provider; in case of rsyslog-ksi-ls12 package this is "ksi_ls12".

  • sig.block.levelLimit defines the maximum level of the root of the local aggregation tree per one block. The maximum number of log lines in one block is calculated as 2^(levelLimit - 1).

  • sig.aggregator.url defines the endpoint of the KSI signing service in KSI Gateway. In async mode it is possible to specify up to 3 endpoints for high availability service, where user credentials are integrated into URL. Supported URI schemes are:

    • ksi+http://

    • ksi+tcp://


    • sig.aggregator.url=”ksi+tcp://signingservice1.example.com”


      sig.aggregator.key= “secret”

    • sig.aggregator.url=”ksi+tcp://rsmith:secret@signingservice1.example.com|ksi+tcp://jsmith:terces@signingservice2.example.com”

  • sig.aggregator.user specifies the login name for the KSI signing service. For high availability service, credentials are specified in URI.

  • sig.aggregator.key specifies the key for the login name. For high availability service, credentials are specified in URI.

Optional parameters (if not defined, default value is used):

  • sig.syncmode defines the signing mode: "sync" (default) or "async".

  • sig.hashFunction defines the hash function to be used for hashing, default is "SHA2-256". Other SHA-2, as well as RIPEMED-160 functions are supported.

  • sig.block.timeLimit defines the maximum duration of one block in seconds. Default value "0" indicates that no time limit is set.

  • sig.block.signTimeout specifies a time window within the block signatures have to be issued, default is 10. For example, issuing 4 signatures in a second with sign timeout 10s, it is possible to handle 4 x 10 signatures request created at the same time. More than that, will close last blocks with signature failure as signature requests were not sent out within 10 seconds.

  • sig.aggregator.hmacAlg defines the HMAC algorithm to be used in communication with the KSI Gateway. This must be agreed on with the KSI service provider, default is "SHA2-256".

  • sig.keepTreeHashes turns on/off the storing of the hashes that were used as leaves for building the Merkle tree, default is "off".

  • sig.keepRecordHashes turns on/off the storing of the hashes of the log records, default is "on".

  • sig.confInterval defines interval of periodic request for aggregator configuration in seconds, default is 3600.

  • sig.randomSource defines source of random as file, default is "/dev/urandom".

  • sig.debugFile enables libksi log and redirects it into file specified. Note that logger level has to be specified (see sig.debugLevel).

  • sig.debugLevel specifies libksi log level. Note that log file has to be specified (see sig.debugFile).

    • 0 None (default).

    • 1 Error.

    • 2 Warning.

    • 3 Notice.

    • 4 Info.

    • 5 Debug.

The log signature file, which stores the KSI signatures and information about the signed blocks, appears in the same directory as the log file itself.


To sign the logs in /var/log/secure with KSI:

# The authpriv file has restricted access and is signed with KSI
authpriv.*  action(type="omfile" file="/var/log/secure"

Note that all parameter values must be between quotation marks!

See Also

To better understand the log signing mechanism and the module’s possibilities it is advised to consult with:

Access for both of these documents requires Guardtime tryout service credentials, available from https://guardtime.com/technology/blockchain-developers

See also

Help with configuring/using Rsyslog:

See also

Contributing to Rsyslog:

Copyright 2008-2023 Rainer Gerhards (Großrinderfeld), and Others.