NFD » ndn-cxx

Public key Info Base (PIB) Service

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## Public Key Info Management 

NDN data packets are secured through digital signatures.

In order to generate a valid signature, an NDN application needs to know not only the correct key to use but also the correct public key information that should be put into the `KeyLocator` of a data packet. 

The information needs to be managed locally on the system where the application is running.

The information related to keys is managed at three granularities: identities, keys, and certificates. 

A key is always associated with a namespace, called "identity".

An identity however may have more than one keys.

Each key is named as `/<Identity>/[KeyId]`. 

The `KeyId` uniquely identifies a key which belongs to the `Identity`.

Among these keys, only one is the default key of the identity.

If only identity is provided when signing a packet, the default key of the identity will be used to sign the packet.

A certificate is always associated with the key in the certificate

If a certificate is provided when signing a packet, the corresponding private key should be used to sign the packet 

and the name of the certificate name may be put into the `KeyLocator` of the packet.

A key may have more than one certificates (e.g., certificates may be issued by different parties).

Among these certificates, only one is the default certificate of the key.

The default certificate of the default key of an identity is the default certificate of the identity.

If only identity is provided when signing a packet, the name of the default certificate of the identity may be put into the `KeyLocator` of the packet.

All the information above may be accessed by different APIs and applications on the same system, 

therefore it is desirable to make the information provisioning as a system service. 

Since public keys and certificates are supposed to be publicly available, 

the service also serves as a local storage of certificate and public keys, 

besides providing the public key related information.

## PIB management model

The public key information of each system user is managed separately in PIB.

For now, PIB service is a system service (i.e., run by root).

PIB service may be separated into several user services (i.e., run by each user) in the future.

Each user has three tables in PIB: identity table, key table, and certificate table.

The public key information of a user is managed in these tables.

Identity table consists of two columns: `identity` (primary key) and `default_key_id`.

Identity table schema:

    User_[UserName]_ID(

        identity             BLOB NOT NULL,        

        default_key_id       BLOB,

        PRIMARY KEY (identity)                     

    );                                             

Key Table consists of five columns: `identity`, `key_id`, `key_type`, `key_bits`, and `default_cert_name`. 

The combination of `identity` and `key_id` is the primary key of key table.

Key table schema:

    User_[UserName]_KEY(

        identity             BLOB NOT NULL,        

        key_id               BLOB NOT NULL,        

        key_type             INTEGER NOT NULL,     

        key_bits             BLOB NOT NULL,        

        default_cert_name    BLOB,                 

        PRIMARY KEY (identity, key_id)             

    );

Certificate table consists of four columns: `certificate_name` (primary key), `identity`, `key_id`, and `certificate_data`.

Certificate table schema:

    User_[UserName]_CERT(

        certificate_name     BLOB NOT NULL,        

        identity             BLOB NOT NULL,        

        key_id               BLOB NOT NULL,        

        certificate_data     BLOB NOT NULL,        

        PRIMARY KEY (certificate_name)             

    );

Besides the tables for each user, PIB has two more management tables: user table and certificate_publishing table.

User table stores user's local management key (we will discuss it later) and user's default identity

Each user has its own default identity. 

From the default identity, the default key and certificate of the user can be derived.

User table schema:

    User(                                       

        user_name             BLOB NOT NULL,    

        has_default_identity  INTEGER DEFAULT 0,

        default_identity      BLOB,             

        local_management_cert BLOB NOT NULL,    

        PRIMARY KEY (user_name)                 

    );

Certificate_Publishing table schema:

    Certificate_Publishing(

        user_name             BLOB NOT NULL,

        publish_namespace     BLOB NOT NULL,

        PRIMARY KEY (user_name, publish_namespace)

    );  

The read access to a user's public key information is not restricted,

while the write access to a user's public key information requires authentication.

The write access is expressed as signed commands. 

The signing key can be authenticated only if the key already exists in the corresponding user's PIB tables.

Each key has its own write access privilege which is defined as:

* The root user has the **root key** of the local system. The root key has the highest privilege, i.e., its owner is allowed to change anything in PIB. The identity of the root key is `/localhost`, and the name of the root key should be `/localhost/[KeyId]`.

* Each user has its own **local management key**. The local management key is allowed to change anything in the user's PIB info including the three tables and user's own entry in the user table. The identity of the user local management key is `/localhost/user/[UserName]`, and the name of the key should be `/localhost/user/[UserName]/[KeyId]`. Note that the local management key of the root user is the root key.

* All the other keys are called **regular keys**. A regular key is allowed to change keys/certificates with identities under the key's own namespace, e.g., a key with the identity `/ndn/ucla/alice` is allowed to change a key with the identity `/ndn/ucla/alice/chat` but is not allowed to change a key with the identity `/ndn/ucla/bob`.

## PIB Service Protocol 

PIB service provides an interface to NDN applications for public key info lookup. 

The interface is defined in terms of NDN packets (interest/data).

A query to PIB is expressed as a **[signed interest](http://redmine.named-data.net/projects/ndn-cxx/wiki/SignedInterest)**.

The query interest is defined as:

    /localhost/pib/[UserName]/[Verb]/[Param]/<signed_interest_security_components>

`UserName` indicates the tables in which the query should apply.

`Verb` indicates the access operation. 

Four types of operations are defined: `get` (Read), `search` (Read), `update` (Write), and `delete` (Write).

The operation `get` and `search` are quite similar to each other. 

The only difference is that the response to `get` is the queried entity per se while the response to `search` operation is the existence (a boolean value) of the queried entity.

`Param` is a TLV block containing parameters of the query.

Different types of operations have their own parameters.

### `Get` Parameters

For `get` operation, `Param` is defined as:

       GetParam := Type

                   Filter

         Filter := Name | DefaultOf | ListOf

      DefaultOf := EntityDesc

         ListOf := EntityDesc

     EntityDesc := Type

                   Name

           Type := ID | KEY | CERT

`Type` indicates which table the query will be applied eventually.

`Filter` indicates how to apply the query. 

When `Name` is specified in `Filter`, PIB will directly lookup the entry with the same name in the table indicated by `Type`.

When `DefaultOf` is specified in `Filter`, PIB will first derive the name of the target through the default information and lookup the entry in the table indicated by `Type`.

When `ListOf` is specified in `Filter`, PIB will collect all the entries that satisfy the condition specified in `ListOf`. 

Here are some examples of `GetParam`:

    GetParam 

    {

      Type: KEY

      Filter 

      {  

        Name: /ndn/edu/ucla/ksk-1234

      }

    }

The example above is a query to get a key with the name `/ndn/edu/ucla/ksk-1234`.

    GetParam

    {

      Type: CERT

      Filter 

      { 

        DefautOf 

        {

          Type: ID

          Name: /ndn/edu/ucla/alice

        }

      }

    }

The example above is a query to get the default certificate of an identity `/ndn/edu/ucla/alice`.

    GetParam

    {

      Type: CERT

      Filter 

      { 

        ListOf 

        {

          Type: KEY

          Name: /ndn/edu/ucla/ksk-1234

        }

      }

    }

The example above is a query to get a list of certificates of a key `/ndn/edu/ucla/alice`.

### `Search` Parameters

The parameters of `search` operation is quite similar to `get` operation except that there is no `ListOf` filter.

    SearchParam := Type

                   Filter

         Filter := Name | DefaultOf

      DefaultOf := EntityDesc

     EntityDesc := Type

                   Name

           Type := ID | KEY | CERT

The response to `search` operation is a boolean value to indicate the existence of the searched entity 

### `Update` Parameters

The parameters of `update` operation are defined as: 

    UpdateParam := Entity

                   DefaultOpt

         Entity := Identity | PublicKey | Certificate

       Identity := Name

      PublicKey := Name

                   Bytes

    Certificate := Bytes

     DefaultOpt := USER_DEFAULT | ID_DEFAULT | KEY_DEFAULT | NO_DEFAULT

The operation, once validated, will add a new entry in the corresponding table if no such an entry exists or update the existing entry,

and change the default setting according to `DefaultOpt`.

### `Delete` Parameters

The parameters of `delete` operation are defined as: 

    DeleteParam := EntityDesc

     EntityDesc := Type

                   Name

           Type := ID | KEY | CERT

The entity and its belonging entities will be deleted once the operation is validated.

### TLV-TYPE assignments

Type                                        | Assigned value    | Assigned value (hex)

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

GetParam                                    | 128               | 0x80

SearchParam                                 | 129               | 0x81

UpdateParam                                 | 130               | 0x82

DeleteParam                                 | 131               | 0x83

Type                                        | 132               | 0x84

Filter                                      | 133               | 0x85

Name                                        | 134               | 0x86

DefaultOf                                   | 135               | 0x87

ListOf                                      | 136               | 0x88

EntityDesc                                  | 137               | 0x89

Entity                                      | 138               | 0x8a

Identity                                    | 139               | 0x8b

PublicKey                                   | 140               | 0x8c

Certificate                                 | 141               | 0x8d

Bytes                                       | 142               | 0x8e 

DefaultOpt                                  | 143               | 0x8f 

### Constant value assignments

For type `Type`:

Constant                                    | Assigned value    | Assigned value (hex)

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

ID                                          | 0                 | 0x00

KEY                                         | 1                 | 0x01

CERT                                        | 2                 | 0x02

For type `DefaultOpt`:

Constant                                    | Assigned value    | Assigned value (hex)

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

NO_DEFAULT                                  | 0                 | 0x00

USER_DEFAULT                                | 1                 | 0x01

ID_DEFAULT                                  | 2                 | 0x02

KEY_DEFAULT                                 | 3                 | 0x03

### Query Responses

The response to a query interest is a data packet signed by PIB.

The public key certificate of PIB is stored in a read-only file and is accessible to all users on the system.

The content of the response to `get` operation could be one of the three TLV defined above: `Identity` (0x8b), `PublicKey` (0x8c), and `Certificate` (0x8d), or a list of these TLVs.

The content of the response to `search` operation is a byte. Non-zero byte stands for true while 0x00 stands for false.

The content of the response to `update` or `delete` operation is a byte which serves as an error code. 

0x00 stands for success while non-zero byte stands for failure. 

Error code for `update`:

Error code              | Value             | Description

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

ERR_SUCCESS             | 0                 | No error

Error code for `delete`:

Error code              | Value             | Description

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

ERR_SUCCESS             | 0                 | No error