Layer 2: Cryptographic Layer

Background

Cryptography is employed for permissioning (ex. who can modify databases) and for database consensus.

• Each client application has a public and private key-pair. Any message sent is signed and sent in an envelope. (See Bluzelle's Protobuf API).

  • The private key is an argument to the Bluzelle client.

  • The public key can be generated from the private key.

Specifications

• All Bluzelle keys are ECDSA on the curve secp256k1.

• The client must accept a key argument in a way that is reasonable to the application. For desktop applications, this may be through a .pem file on the filesystem. For web applications, it may be through an argument.

Outgoing Messages

1. Given a completed message that is a database_msg or status_request, serialize it and embed it as the appropriate payload type in the bzn_envelope.

2. If the message was a status_request, we are done. Otherwise, continue to the signing process.

3. Fill in the timestamp field with current time as milliseconds since UNIX epoch (seen here).

4. Fill in the sender field with the public key in PEM format. It should look like this: "MFYwEAYHKoZIzj0CAQYFK4EEAAoDQgAEY6L6fb2Xd9KZi05LQlZ83+0pIrjOIFvy0azEA+cDf7L7hMgRXrXj5+u6ys3ZSp2Wj58hTXsiiEPrRMMO1pwjRg=="

5. The last step is to fill in the signature. Follow these steps closely:

   1. Take the sender, payloadCase (you should be able to get it from protobuf), payload, and timestamp.

   2. Encode them as ascii.

   3. For each ascii string, create a new string that contains its length, a pipe character, then the string itself. For example, the timestamp would be 13|1549394321578.

   4. Concatenate all of the strings in the same order that they were given. Empty message example: "120|MFYwEAYHKoZIzj0CAQYFK4EEAAoDQgAEHLmWG+xY1lZak68iQMFCh2Vm1EfkEOkbclWWbEO1s+qpf6D6D/Yjo9CR2/zLHWkgTqo71nnjWWEU5FekTHjVmQ==2|100|1|0"

   5. Convert this string to binary with ascii as the encoding.

   6. Sign the binary with the ECDSA private key.

   7. Embed the signature in the bzn_envelope.

Incoming Messages

• Cryptography is not verified for incoming messages. Interpret the payload as a database_response or status_response and continue to higher layers.