NFD » ndn-cxx

# Validator Configuration File Format

You can set up a `Validator` via a configuration file. 

Next, we will show you how to write a configuration file.

The configuration file consists of **rules** that will be used in validation.

Here is an example of configuration file containing two rules.

    rule

    {

      id "Simple Rule"

      for data

      type customized

      filter

      {

        type name

        name /localhost/example

        relation isPrefixOf

      }

      signer

      {

        sig-type rsa-sha256

        key-locator

        {

          type name

          name /ndn/edu/ucla/KEY/yingdi/ksk-1234/ID-CERT

          relation equal

        }

      }

    }

    rule

    {

      id "Testbed Validation Rule"

      for data

      type hierarchical

      filter

      {

        type name

        regex ^<>*$

      }

      trust-anchor

      {

        type file

        file-name "testbed-trust-anchor.cert"

      }

    }

<font color='red'>**ATTENTION: The order of rules MATTERS!**</font>

A rule can be broken into two parts: 

* The first part is to qualify packets to which the rule can be applied;

* The second part is to decide whether further validation process is necessary.

When receiving a packet, the validator will check it against rules in the configuration file one-by-one,

until reaching a rule that the packet qualifies for.

And the second part of the matching rule will be used to check the validity of the packet.

If the packet cannot qualify any rules, it is treated as an invalid packet.

Once a packet has been matched by a rule, it will not be checked against the rest rules.

Therefore, you should always put the most specific rule to the top, otherwise it will become useless.

In the example configuration,

the first rule indicates that all the data packets under the name prefix "/localhost/example" must be signed by a key whose certificate name is "/ndn/edu/ucla/KEY/yingdi/ksk-1234/ID-CERT".

If a packet does not have a name under prefix "/localhost/example", validator will skip the first rule and check the second rule.

The second rule indicates that any data packets must be validated recursively back along a hierarchy with a trust anchor stored in a file called "testbed-trust-anchor.cert".

## Rules in general

Before we go into the details of specific rules, we need to introduce several general properties of a rule.

A rule must have a **id** property which uniquely identifies the rule in the configuration file, e.g., "Simple Rule", "Testbed Validation Rule".

A rule is either used to validate an interest packet or a data packet. 

This information is specified in the property **for**.

Only two value can be specified: **data** and **interest**.

The property **type** indicates the type of rules.

There are some pre-defined rule types, such as **hierarchical**.

You can also customize their own rules by setting the type property to be **customized**.

A rule may have some other properties depending on the rule type. 

Next, we will introduce the other properties for the each rule type.

## Customized Rule

Two properties are required by customized rule: **filter** and **signer**.

### Filter Property

The **filter** property specifies the condition that a packet must fulfill.

A rule may contain more than one filters.

A packet can be captured by a rule only if the packet satisfies all the filters.

Filter has its own property **type**.

Although a rule may contain more than one filters, there is at most one filter of each type.

So far, only one filter type is defined: **name**.

In other word, only one filter can be specified for now.

There are two ways to express the restrictions on name. 

The first way is to specify a relationship between the packet name and a particular name.

In this case, two more properties are required: **name** and **relation**.

A packet can fulfill the condition if the **name** and the packet name can establish the **relation**.

Three types of **relation** are defined: **equal**, **isPrefixOf**, **isStrictPrefixOf**. 

For example, a filter 

    filter

    {

      type name

      name /localhost/example

      relation equal

    }

can only catch a packet with the exact name "/localhost/example".

And a filter

    filter

    {

      type name

      name /localhost/example

      relation isPrefixOf

    }

can capture a packet with name "/localhost/example" or "/localhost/example/data", but cannot catch a packet with name "/localhost/another_example".

And a filter

    filter

    {

      type name

      name /localhost/example

      relation isStrictPrefixOf

    }

can capture a packet with name "/localhost/example/data", but cannot catch a packet with name "/localhost/example".

The second way is to specify an [[Regex|NDN Regular Expression]] that can match the packet.

In this case, only one property **regex** is required.

For example, a filter 

    filter

    {

      type name

      regex ^[^<KEY>]*<KEY><>*<ksk-.*><ID-CERT>$

    }

can catch all the identity certificates. 

### Signer Property

The **signer** property defines the conditions that the `SignatureInfo` part of the packet must fulfill.

Same as the **filter** property, a rule may contain more than one **signer** properties.

A packet, however, only needs to satisfy one of the **signer** properties.

A signer property requires a **sig-type** property which specifies the acceptable signature type.

Right now only one signature type **rsa-sha256** is defined.

A signer property also requires a **key-locator** property which specifies the conditions on `KeyLocator`.

Right now only one key-locator type **name** is defined.

Such a type of key-locator contains the certificate name of the signing key.

Since the key-locator is a name, you can specify the conditions on it in the same way as the **filter** with type **name**.

For example, a signer could be:

    signer

    {

      sig-type rsa-sha256

      key-locator

      {

        type name

        name /ndn/edu/ucla/KEY/yingdi/ksk-1234/ID-CERT

        relation equal

      }

    }

This signer property requires that the packet must have a rsa-sha256 signature generated by a key whose certificate name is "/ndn/edu/ucla/KEY/yingdi/ksk-1234/ID-CERT".

Besides the two ways to express conditions on key-locator name (name and regex), 

you can further constrain the key-locator name using the information extracted from the packet name.

This third type of condition is expressed via a property **hyper-relation**.

The **hyper-relation** property consists of three parts:

* an NDN regular expression that can extract information from packet name

* an NDN regular expression that can extract information from key-locator name

* relation between the two parts above

For example, a signer:

    signer

    {

      sig-type rsa-sha256

      key-locator

      {

        type name

        hyper-relation

        {

          p-regex ^(<>*)$

          p-expand \1

          k-regex ^([^<KEY>]*)<KEY>(<>*)<ksk-.*><ID-CERT>$

          k-expand \1\2

          relation isPrefixOf

        }

      }

    }

requires the packet name must be under the corresponding namespace of the key-locator name.

In some cases, the signer property may contain a **trust-anchor** property which specifies the pre-trusted certificate.

For example, a signer with a trust-anchor property could be:

    signer

    {

      sig-type rsa-sha256

      key-locator

      {

        type name

        hyper-relation

        {

          p-regex ^(<>*)$

          p-expand \1

          k-regex ^([^<KEY>]*)<KEY>(<>*)<ksk-.*><ID-CERT>$

          k-expand \1\2

          relation isPrefixOf

        }

      }

      trust-anchor

      {

        type file

        file-name "testbed-trust-anchor.cert"

      }

    }

Note that the **trust-anchor** must fulfill the conditions specified in **sig-type** and **key-locator**.

## Hierarchical Rule

As implied by its name, hierarchical rule requires that the packet name must be under the namespace of the packet signer.

Therefore, you only need to specify two properties in hierarchical rule: 

* a filter of type name which restrict the scope of packets

* trust-anchors of the hierarchy

For the hierarchical rule in the example configuration, it is equivalent to a customized rule:

    rule

    {

      id "Testbed Validation Rule"

      for data

      type customized

      filter

      {

        type name

        regex ^(<>*)$

        expand \1

      }

      signer

      {

        sig-type rsa-sha256

        key-locator

        {

          type name

          hyper-relation

          {

            p-regex ^(<>*)$

            p-expand \1

            k-regex ^([^<KEY>]*)<KEY>(<>*)<ksk-.*><ID-CERT>$

            k-expand \1\2

            relation isPrefixOf

          }

        }

        trust-anchor

        {

          type file

          file-name "testbed-trust-anchor.cert"

        }

      }

    }

## Example Configuration For NLSR

The trust model of NLSR is semi-hierarchical.

An example certificate signing hierarchy is:

                                            root 

                                             |  	    

                              +--------------+---------------+

                            site1                          site2

                              |                              |		   

                    +---------+---------+                    +

                 operator1           operator2            operator3

                    |                   |                    | 

              +-----+-----+        +----+-----+        +-----+-----+--------+

           router1     router2  router3    router4  router5     router6  router7

              |           |        |          |        |           |        |

              +           +        +          +        +           +        +  	      

            NLSR        NSLR     NSLR       NSLR     NSLR        NSLR     NSLR

However, entities name may not follow the signing hierarchy, for example:

Entity   | Identity Name                                     | Example                         | Certificate Name Example

-------- | ------------------------------------------------- | ------------------------------- | ------------------------------------------------

root     | /\<network\>                                      | /ndn                            | /ndn/KEY/ksk-1/ID-CERT/%01

site     | /\<network\>/\<site\>                             | /ndn/edu/ucla                   | /ndn/edu/ucla/KEY/ksk-2/ID-CERT/%01

operator | /\<network\>/\<site\>/%C1.O.N./\<operator-id\>    | /ndn/edu/ucla/%C1.O.N./op1      | /ndn/edu/ucla/%C1.O.N./op1/KEY/ksk-3/ID-CERT/%01

router   | /\<network\>/\<site\>/%C1.O.R./\<router-id\>      | /ndn/edu/ucla/%C1.O.R./rt1      | /ndn/edu/ucla/%C1.O.R./rt1/KEY/ksk-4/ID-CERT/%01

NLSR     | /\<network\>/\<site\>/%C1.O.R./\<router-id\>/NLSR | /ndn/edu/ucla/%C1.O.R./rt1/NLSR | /ndn/edu/ucla/%C1.O.R./rt1/NLSR/KEY/ksk-5/ID-CERT/%01

Assume that a typical NLSR data name could be "/ndn/edu/ucla/%C1.O.R./rt1/NLSR/LSA/LSType.1/%01".

Then, the only place where naming hierarchy is broken is "operator->router".

So we can write a configuration file with three rules.

The first one is a customized rule that capture the normal NLSR data.

The second one is a customized rule that handles the exception case of the hierarchy (operator->router).

And the last one is a hierarchical rule that handles the normal cases of the hierarchy.

We put the NLSR data rule to the first place, because NLSR data packets are the most frequently checked.

The hierarchical exception rule is put to the second, because it is more specific than the last one.

And here is the configuration file:

    rule

    {

      id "NSLR LSA Rule"

      for data

      type customized

      filter

      {

        type name

        regex ^[^<NLSR><LSA>]*<NLSR><LSA>

      }

      signer

      {

        sig-type rsa-sha256

        key-locator

        {

          type name

          hyper-relation

          {

            p-regex ^([^<NLSR><LSA>]*)<NLSR><LSA><LSType\.\d><>$

            p-expand \1

            k-regex ^([^<KEY>]*)<KEY><ksk-.*><ID-CERT>$

            k-expand \1

            relation equal

          }

        }

      }

    }

    rule

    {

      id "NSLR Hierarchy Exception Rule"

      for data

      type customized

      filter

      {

        type name

        regex ^[^<KEY><%C1.O.R.>]*<%C1.O.R.><><KEY><ksk-.*><ID-CERT><>$

      }

      signer

      {

        sig-type rsa-sha256

        key-locator

        {

          type name

          hyper-relation

          {

            p-regex ^([^<KEY><%C1.O.R.>]*)<%C1.O.R.><><KEY><ksk-.*><ID-CERT><>$

            p-expand \1

            k-regex ^([^<KEY><%C1.O.N.>]*)<%C1.O.N.><><KEY><ksk-.*><ID-CERT>$

            k-expand \1

            relation equal

          }

        }

      }

    }

    rule

    {

      id "NSLR Hierarchical Rule"

      for data

      type hierarchical

      target

      {

        type name

        regex ^([^<KEY>]*)<KEY><ksk-.*><ID-CERT><>$

      }

      trust-anchor

      {

        type file

        file-name "testbed-trust-anchor.cert"

      }

    }