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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 bound. 

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.

Each user has its own default identity. 

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

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 authentication rules are defined as: 

* Each user has a 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).

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