This article describes the concept of chained signature for object history in Smart ID Identity Manager.

To allow deletion of older entries, the deletion of object history can be limited to a window of the previous N months, with N being >= 12. Smaller values will be overridden by 12.

In the object history, all changes on each object (employees, cards, certificates, requests etc.) are tracked. This can, for example, be that data is changed, status (like deactivate card) is changed, or if a process is executed (start Smart ID Mobile App provisioning) etc. This history is signed, so that it is recognized if someone modifies the records in the database. Chained signature means that each entry of the object history is signed. The signature is based on the signature of the previous entry, so it is not possible to add, remove or change an entry without breaking the chain. Thus every manipulation of the object history can be detected as long as the head of the chain is protected. The chained signature spans over all history entries, regardless of tenant.

Prerequisites

The certificates used for signing and verification need to be valid for digital signatures. Otherwise Identity Manager will fail on writing to the database.

Upgrade instruction

Upgrade to 22.04 (or later) from an earlier version

The parameter commonHistoryService.verificationIntervalMonths in Identity Manager Operator's system.properties was renamed to commonHistoryService.historyCutOffDuration in Smart ID 22.04. Make sure you rename it accordingly in your configuration. See also List of Identity Manager system properties.
Add/update the following section and configure it as desired (explained further down in this document).
The default CRON expression for the history cleaning task has been added to be executed on Fridays only. This is a new property added for the history cleaning task:

# History cleaning task
historyCleaningTrigger.cronExpression = 0 30 0 ? * FRI *

Furthermore, the default CRON expression for the history verification task has changed, so it executes only on Sundays, not daily:

# History verification task
historyVerificationTrigger.cronExpression = 0 30 0 ? * SUN *

Configure chained signature

The keys and certificates used for signing and verification are configured in the encrypt and sign engine's configuration, typically found under engineSignEncryptConfig.xml.

Configure the key used for the chained signature via the property descriptorName of the bean historyServiceSigner. Add the following to system.properties:
Add key for chained signature
```
historyServiceSigner.descriptorName=<name of the descriptor>
```
If the chained signature is not configured, Tomcat startup will fail with an error message like:
Error message from Tomcat
```
Error accessing the sign and encrypt engine (5, No descriptor found with name: overwriteMe)
```

Verify chained signature

Verification consists of traversing over all entries of the object history, regardless of tenant, and verifying its signature.

Manual verification

Verify the chained signatures with a REST service call to this url:
URL for manual verification of chained signature

<prime-explorer>/ws/objecthistory/verify[?tenantId=<tenant for login>]

where the tenantId is optional.
The login can be done via basic authentication. For example, if you log in as admin/admin the following header is added, where YWRtaW46YWRtaW4= is the "admin:admin" Base64-encoded:
```
Authorization: Basic YWRtaW46YWRtaW4=
```
Some REST service clients support convenient entry of basic authentication with fields. If preemptive authentication is offered, you should use that, since the REST service do not ask for authentication, but rather just fail if no authentication is offered.
The result is either 'true' if everything is fine or 'false' if a verification failed. Details about verification errors are listed in a log file.

A successful verification is only possible if at least one entry is already signed.

Scheduled verification

A scheduled job regularly checks the signature chain of the object history. If an error is found, it will send an email to configurable recipients.

As the object history signature spans over all history entries, regardless of the tenant, the verification on a multi tenant system should be done by a dedicated user that belongs to no tenant (that is, it has a null tenantId), but who performs this task for the whole system. Use the Identity Manager Tenant application to create such a user:

In system.properties, set the following (also needed for "scheduled cleaning" below):

Add user for scheduled task in system.properties

# System user for scheduled tasks. Executes tasks relevant to ALL tenants.
# Username
cronUsername.encrypted=admin
# Password
cronPassword.encrypted=admin

Configure the SMTP server in Identity Manager. See Set up email template in Identity Manager.

Several attributes can be configured in system.properties. Note that a property may span over several lines by ending intermediate lines with a backslash. At the very least, you must configure a recipient.
This is an example of system.properties:

system.properties

# When to execute. Fields: Seconds Minutes Hours Day-of-Month Month Day-of-Week Year(optional)
historyVerificationTrigger.cronExpression = 0 30 0 ? * SUN *

# Email address of users to be notified by scheduling jobs.
# Next line is mandatory!
#schedulingReporter.to =
#schedulingReporter.cc =
# Subject and contents of the mail to send on verification errors
historyVerificationJobDetail.jobDataMap[subject] = Error verifying object history signature
historyVerificationJobDetail.jobDataMap[text] = Hi there,\n\
something has gone wrong with the object history signature.\n\
For more details, please have a look at the server log.\n\
\n\

Also see "Define Cut-Off For Verification / Cleanup Window" below!

Delete old history entries

The periodically running HistoryCleaningJob deletes history entries that are no longer needed for verification in the current verification window, as defined by the configured cut-off (see below).

Scheduled Cleaning

A scheduled job regularly cleans the signature chain of the object history.

As the object history signature spans over all history entries, regardless of the tenant, the cleaning on a multi tenant system should be done by a dedicated user that belongs to no tenant (that is, it has a null tenantId), but who performs this task for the whole system. Use the Identity Manager Tenant application to create such a user:

In system.properties, set the following (also needed "scheduled verification" above):

Add user for scheduled task in system.properties

# System user for scheduled tasks. Executes tasks relevant to ALL tenants.
# Username
cronUsername.encrypted=admin
# Password
cronPassword.encrypted=admin

Several attributes can be configured in system.properties. Note that a property may span over several lines by ending intermediate lines with a backslash.
This is an example of system.properties:
system.properties
```
# When to execute. Fields: Seconds Minutes Hours Day-of-Month Month Day-of-Week Year(optional) 
historyCleaningTrigger.cronExpression = 0 30 0 ? * FRI * 
```
Also see "Define Cut-Off For Verification / Cleanup Window" below!

Define cut-off for verification/cleanup window

By default the verification windows spans the entire history. You can limit it to the last N >= 12 months. This will enable deletion of older entries outside the verification window.

Configure verification/deletion cut-off

The verification of object history can be limited to a window of the most recent N months, with N being >= 12. Smaller values will be overridden by 12.

This will also enable cleanup of older entries outside the verification window to reduce the amount of stored data.

The cleanup process is irreversible, so be careful on how you configure the verification window before you run the deletion job for the first time!

If no cut-off is specified, the entire history is validated (default), and cleanup has no effect.

Enter this in system.properties to specify a window starting 12 months in the past and ending at the current time:
Specify timeframe in system.properties
```
# new parameter name in IDM 2204 (used to be "commonHistoryService.verificationIntervalMonths")
commonHistoryService.historyCutOffDuration=12
```

Note that if a verification window is set, the following applies:

verification will fail if the oldest entry of any chain within the verification window points to a deleted predecessor
if verification fails for entries outside the verification window, this will be logged

Clustering

In a clustered environment there is a separate chain per cluster node. With the default configuration, the chain's name is derived from the cluster node, that is, the jvmRoute attribute of the engine tag found in the server.xml. The implementation uses only the primary engine and does not support any special cases.

If there is a special cluster configuration, or if a cluster is not based on a unique jvmRoute per node, the attribute commonHistoryService.chainName needs to be provided. If this attribute is not found, like typically in single node environments, PRIME1 is used as default name.

Multitenancy

Each history entry corresponds to an action that was performed on a core object in Identity Manager. Thus it belongs to a single tenant. The chained signature of the history on the other hand is global: there's exactly one chain for each cluster node, that spans over all history entries, regardless of the tenant. The signature ensures that no history entry of a Identity Manager cluster node has been manipulated.

For this reason it is recommended that the signature verification is performed by an administrator that is not bound to a tenant, that is, with an tenantId of null. The scheduled task that performs history verification should, in case of an error, be configured to send an email to a global user that administers Identity Manager for all tenants. It is still possible to verify the signatures with a user belonging to a tenant, but this should only be done on single tenant systems.

This article is valid for Smart ID 22.04 and later.

Chained signature for object history in Identity Manager