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).

Depending on the query type, a query to PIB is expressed as a **[signed interest](http://redmine.named-data.net/projects/ndn-cxx/wiki/SignedInterest)** (for Write operation) or normal interest (for Read operation).

The query interest is defined as:

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

                                            |<-- Required for Write operation -->|

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

`Verb` indicates the access operation. 

Five types of operations are defined: 

Verb                 | Access Type       | Description

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

Get                  | Read              | Get a single entity (user, identity, key, or certificate)

Default              | Read              | Get the default setting of an entity

List                 | Read              | List the name of a set of entities

Update               | Write             | Add/Change an entity

Delete               | Write             | Delete an entity

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

Different types of operations have their own parameters.

### 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.

Several TLVs are defined for the content of query responses.

`Identity` TLV:

    PibIdentity := PIB-IDENTITY-TYPE TLV-LENGTH

                   Name

`PublicKey` TLV:

    PibPublicKey := PIB-PUBLIC-KEY-TYPE TLV-LENGTH

                    Name

                    PibBytes

`Certificate` TLV:

    PibCertificate := PIB-CERTIFICATE-TYPE TLV-LENGTH

                      Data 

A response may also be a error code defined a non-negative integer:

     Response := CONTENT-TYPE TLV-LENGTH

                 ErrorCode

                 Bytes

    ErrorCode := ERROR-CODE-TYPE TLV-LENGTH

                 nonNegativeInteger

Error code                    | Value             | Description

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

ERR\_SUCCESS                  | 0                 | No error

ERR\_INCOMPLETE\_COMMAND      | 1                 | Incomplete interest

ERR\_WRONG\_VERB              | 2                 | Wrong verb in interest

ERR\_WRONG\_PARAM             | 3                 | Wrong parameter in interest

ERR\_NON\_EXISTING\_USER      | 128               | User does not exist

ERR\_NON\_EXISTING\_ID        | 129               | Identity does not exist

ERR\_NON\_EXISTING\_KEY       | 130               | Public key does not exist

ERR\_NON\_EXISTING\_CERT      | 131               | Certificate does not exist

ERR\_NO\_DEFAULT\_ID          | 256               | No default identity is set

ERR\_NO\_DEFAULT\_KEY         | 257               | No default public key is set 

ERR\_NO\_DEFAULT\_CERT        | 258               | No default certificate is set

ERR\_DELETE\_DEFAULT\_SETTING | 384               | Trying to delete default setting

### `Get` Parameters

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

    PibGetParam := PIB-GET-PARAM-TYPE TLV-LENGTH

                   PibType

                   Name?

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

    PibType := PIB-TYPE-TYPE TLV-LENGTH

               nonNegativeInteger

Type constant                               | Assigned value    | Assigned value (hex)

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

USER                                        | 0                 | 0x00

ID                                          | 1                 | 0x01

KEY                                         | 2                 | 0x02

CERT                                        | 3                 | 0x03

`Name` is the name of the queried entity. It is a TLV defined in [NDN-TLV spec](http://named-data.net/doc/ndn-tlv/name.html#name).

Name is ignored if type is USER.

If error happens during processing the query, the content of the response is an ErrorCode TLV.

If no error happens, the content depends on the `Type`.

When `Type` is `User`, the content is a list of TLVs:

    GetUserContent := CONTENT-TYPE TLV-LENGTH

                      PibCertificate // local management certificate

                      ...            // Other information to add if exists

When `Type` is `ID`, the query is actually invalid. 

The response is an ErrorCode with value `ERR_WRONG_PARAM`.

For `KEY`, the content is a `PibPublicKey` TLV. 

For `CERT`, the content is a `PibCertificate` TLV.

### `Default` Parameters

The parameters of `default` operation is defined as.

      PibDefaultParam := PIB-DEFAULT-PARAM-TYPE TLV-LENGTH

                         PibType    // target type

                         PibType    // origin type

                         Name?      // origin name

The response to a `default` query is the default entity of the "target type" of the "origin".

Possible values of target type include `ID`, `KEY`, and `CERT`.

Possible values of origin type include `USER`, `ID`, and `KEY`.

The target type should be always "below" the origin type (e.g., it is wrong to have a target type `ID` and an origin type `CERT`.)

The origin name should be consistent with the origin type.

Origin name is ignored if origin type is `USER`.

When wrong parameters are supplied, the content of response is an ErrorCode with value `ERR_WRONG_PARAM`.

If no error happens in processing the query, the response could be `PibIdentity`, `PibPublicKey`, or `PibCertificate`, depending on the target type.

### `List` Parameters

The parameters of `list` operation are defined as: 

    PibListParam := PIB-LIST-PARAM-TYPE TLV-LENGTH

                    PibType // origin type

                    Name?   // origin name

The response to the `list` query is a list of `Name`, depending on the origin type.

Possible values of origin type include `USER`, `ID`, and `KEY`.

Origin name is ignored if origin type is `USER`.

If the origin type is `USER`, the response is a list of identities of the user.

If the origin type is `ID`, the response is a list of names of keys of the identity.

If the origin type is `KEY`, the response is a list of names of certificates of the key.

    PibNameList := PIB-NAME-LIST-TYPE TLV-LENGTH

                   Name+

### `Update` Parameters

The parameters of `update` operation are defined as: 

    PibUpdateParam := PIB-UPDATE-PARAM-TYPE TLV-LENGTH

                      (PibIdentity | PibPublicKey | PibCertificate)

                      PibDefaultOpt

`DefaultOpt` is the default option:

    PibDefaultOpt := PIB-DEFAULT-OPT-TYPE TLV-LENGTH

                     nonNegativeInteger

DefaultOpt constant                         | Assigned value    | Assigned value (hex)

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

DEFAULT\_OPT\_NO                              | 0                 | 0x00

DEFAULT\_OPT\_USER                            | 1                 | 0x01

DEFAULT\_OPT\_ID                              | 2                 | 0x02

DEFAULT\_OPT\_KEY                             | 3                 | 0x03

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 `PibDefaultOpt`.

The response is always an ErrorCode: `ERR_SUCCESS` for a successful operation, others for failure.

### `Delete` Parameters

The parameters of `delete` operation are defined as: 

    PibDeleteParam := PIB-DELETE-PARAM-TYPE TLV-LENGTH

                      PibType

                      Name

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

The response is always an ErrorCode: `ERR_SUCCESS` for a successful deletion, others for failure.

### TLV-TYPE assignments

Type                                            | Assigned value    | Assigned value (hex)

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

PibGetParam                                     | 128               | 0x80

PibDefaultParam                                 | 129               | 0x81

PibListParam                                    | 130               | 0x82

PibUpdateParam                                  | 131               | 0x83

PibDeleteParam                                  | 132               | 0x84

PibType                                         | 144               | 0x90

PibIdentity                                     | 145               | 0x91

PibPublicKey                                    | 146               | 0x92

PibCertificate                                  | 147               | 0x93

PibBytes                                        | 148               | 0x94 

PibDefaultOpt                                   | 149               | 0x95

PibNameList                                     | 150               | 0x96

PibErrorCode                                    | 252               | 0xfc