The goal of Provider Records Cryptography in the context of Double Hashing is to provide more reader-privacy while having authenticated Provider Records.

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Definitions

Provider Record

A provider record basically is a pointer to a peerid. It is used in the DHT’s key-value store. The keys are the DHT content identifiers Hash(MH) , which MH being the multihash of the content. The value is the peerid of the peers providing the content associated with Hash(MH). So a provider record is a peerid associated with some content.

Provider Record Encryption

As the Provider Records are stored in the DHT key-value store, indexed by the Hash(MH) they reference, anyone knowing Hash(MH) can retrieve the provider record, and learn about the content provider, if the provider record isn’t encrypted. The Provider Record (peerid) can be encrypted with a key derived from the CID. This would only allow peers knowing CID to read the Provider Record’s content, knowing Hash(MH) wouldn’t be enough. As Delegated Routing instances are going to be edge caches run by external/community entities, encrypting provider records prevents them from targeting specific providers / learning provider popularity

Advantages & Drawbacks of Provider Record Encryption

Advantages:

• Only a peer with the knowledge of the CID (and hence MH) can create a valid encrypted provider record. This provider record can in any case be verified by any client knowing CID.
• Slight writer-privacy increase. The peerid of the content provider is encrypted, and hence cannot be associated with the DHT identifier of some content, namely Hash(MH). However, any adversary with the knowledge of CID still knows the identity of the content provider.
• As the DHT server peer cannot verify if the content of the encrypted peerid corresponds with the multiaddress of the publisher, it could allow nodes to publish/republish content for other peers.

Drawbacks:

• The provider records cannot be authenticated as easily. The DHT server node cannot verify if the Provider Record’s peerid corresponds with the publisher peerid
• Generally adds complexity
• The Encrypted Provider record is expected to contain more bytes than the plaintext one (because of padding, and potentially adding timestamps, authentication layer etc.)

Provider Record Encryption Algorithm

We decided to use AES256 with GCM mode of operation. It is an efficient stream cipher providing authenticated encryption. Hence, it enables clients to verify that the publisher of the encrypted provider record knows the CID.

This algorithm is efficient and quantum-safe.

Provider Record Authentication