NFD » ndn-cxx

Public key Info Base (PIB) Service

==================================

## 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.

PIB service is run as a separate service for each user.

Users' public key information is managed in three tables in PIB: identity table, key table, and certificate table.

Identity table schema:

    Identities(

        id                   INTEGER PRIMARY KEY,

        identity             BLOB NOT NULL,        

        is_default           INETEGER DEFAULT 0

    );

A unique index is created on (identity).

Key table schema:

    Keys(

        id                   INTEGER PRIMARY KEY,

        identity             BLOB NOT NULL,        

        key_id               BLOB NOT NULL,        

        key_type             INTEGER NOT NULL,     

        key_bits             BLOB NOT NULL,        

        is_default           INETEGER DEFAULT 0,

        FOREIGN KEY(identity) REFERENCES identities(identity) ON DELETE CASCADE             

    );    

A unique index is created on (identity, key_id).

Certificate table schema:

    Certificate(

        id                   INTEGER PRIMARY KEY,

        certificate_name     BLOB NOT NULL,        

        identity             BLOB NOT NULL,        

        key_id               BLOB NOT NULL,        

        certificate_data     BLOB NOT NULL,        

        is_default           INETEGER DEFAULT 0,

        FOREIGN KEY(identity, key_id) REFERENCES keys(identity, key_id) ON DELETE CASCADE

    );

A unique index is created on (certificate_name).

Besides these tables  PIB has one more management tables: `mgmt` table.

`mgmt` table stores owner name, corresponding tpm locator, and local management key (we will discuss it later).

User table schema:

    mgmt(                                       

        id                    INTEGER PRIMARY KEY

        owner                 BLOB NOT NULL,

        tpm_locator           BLOB,

        local_management_cert BLOB NOT NULL,    

    );

The read access to PIB is not restricted,

while the write access to PIB 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 local management key is allowed to change anything in the PIB info in the three tables. The identity of the user local management key is `/localhost/pib/user/[UserName]`, and the name of the key should be `/localhost/pib/user/[UserName]/[KeyId]`. Adding a new normal user's local management key is not restricted for now, because we expect in future that OS will prevent a user from registering another user in PIB. However, changing a existing user's local management key requires a signature generated by the existing 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`. Importing a self-signed regular key requires the signature generated by the corresponding user's local management key.

## 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 

`User` TLV:

    PibUser := PIB-USER-TYPE TLV-LENGTH

               Data // local management certificate

               ...  // Other information to add if exists

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

     PibError := PIB-ERROR-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

A response is signed by a PIB instance key with the name `/localhost/pib/[UserName]/dsk-...`.

The PIB instance key is signed by another key with the name `/localhost/pib/[UserName]/ksk-...` which is the trust anchor of the PIB service.

Note that it is difference from the management key name which is `/localhost/pib/`**user**`/[UserName]/dsk-...`.

Management key is used by PIB owner to sign update/delete command interest,

while PIB instance key is used by PIB service to sign PIB responses.

### `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 `ID`, the query is actually invalid. 

The response is an ErrorCode with value `ERR_WRONG_PARAM`.

For `USER`, the content is a `PibUser` TLV.

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

                      (PibUser | 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\_KEY                           | 1                 | 0x01

DEFAULT\_OPT\_ID                            | 3                 | 0x03

DEFAULT\_OPT\_USER                          | 7                 | 0x07

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

PibUser                                         | 151               | 0x97

PibError                                        | 152               | 0x98

PibErrorCode                                    | 252               | 0xfc

## Misc

In that case root user's private key is lost in TPM, you have to delete the root user directly in the database. 

Since the database file is guarded by filesystem, only system admin can do that.