bigchaindb/docs/source/models.md

The Transaction, Block and Vote Models

Transactions, blocks and votes are represented using JSON documents with the following models (schemas). See the section on cryptography for more information about how we calculate hashes and signatures.

The Transaction Model

{
    "id": "<sha3 hash>",
    "version": "<transaction version number>",
    "transaction": {
        "fulfillments": ["<list of <fullfillment>"],
        "conditions": ["<list of <condition>"],
        "operation": "<string>",
        "timestamp": "<timestamp from client>",
        "data": {
            "hash": "<SHA3-256 hash hexdigest of payload>",
            "payload": "<generic json document>"
        }
    }
}

A transaction is an operation between the current_owner and the new_owner over the digital content described by hash. For example if could be a transfer of ownership of the digital content hash

• Transaction header:
  • id: sha3 hash of the transaction. The id is also the DB primary key.
  • version: Version of the transaction. For future compability with changes in the transaction model.
• Transaction body:
  • fulfillments: List of fulfillments. Each fulfillment contains a pointer to an unspent digital asset and a crypto fulfillment that satisfies a spending condition set on the unspent digital asset. A fulfillment is usually a signature proving the ownership of the digital asset. See conditions and fulfillments
  • conditions: List of conditions. Each condition is a crypto condition that needs to be fulfilled by the new owner in order to spend the digital asset. See conditions and fulfillments
  • operation: String representation of the operation being performed (CREATE, TRANSFER, ...) this will define how the transactions should be validated
  • timestamp: Time of creation of the transaction in UTC. It's provided by the client.
  • data: JSON object describing the asset (digital content). It contains at least the field hash which is a sha3 hash of the digital content.

Conditions and Fulfillments

Conditions

Simple Signature

If there is only one new owner the condition will be a single signature condition.

{
    "cid": "<condition index>",
    "condition": {
        "details": {
            "bitmask": "<base16 int>",
            "public_key": "<explain>",
            "signature": null,
            "type": "fulfillment",
            "type_id": "<base16 int>"
        },
        "uri": "<string>"
    },
    "new_owners": ["<list of <base58 string>>"]
}

• Condition header:
  • cid: Condition index so that we can reference this output as an input to another transaction. It also matches the input fid, making this the condition to fulfill in order to spend the digital asset used as input with fid
  • new_owners: List of public keys of the new owners.
• Condition body:
  • bitmask: a set of bits representing the features required by the condition type
  • public_key: the base58 representation of the new_owner's verifying key.
  • type_id: the fulfillment type ID (see the ILP spec)
  • uri: binary representation of the condition using only URL-safe characters

Multi Signature

If there are multiple new owners by default we create a condition requiring a signature from each new owner in order to spend the digital asset.

Example of a condition with two new owners:

{
    "cid": "<condition index>",
    "condition": {
        "details": {
            "bitmask": 41,
            "subfulfillments": [
                {
                    "bitmask": 32,
                    "public_key": "<new owner 1 public key>",
                    "signature": null,
                    "type": "fulfillment",
                    "type_id": 4,
                    "weight": 1
                },
                {
                    "bitmask": 32,
                    "public_key": "<new owner 2 public key>",
                    "signature": null,
                    "type": "fulfillment",
                    "type_id": 4,
                    "weight": 1
                }
            ],
            "threshold": 2,
            "type": "fulfillment",
            "type_id": 2
        },
        "uri": "cc:2:29:ytNK3X6-bZsbF-nCGDTuopUIMi1HCyCkyPewm6oLI3o:206"},
        "new_owners": [
            "<new owner 1 public key>",
            "<new owner 2 public key>"
        ]
}

• subfulfillments: a list of fulfillments
  • weight: integer weight for each subfulfillment's contribution to the threshold
• threshold: threshold to reach for the subfulfillments to reach a valid fulfillment

Fulfillments

Simple Signature

If there is only one current owner the fulfillment will be a single signature fulfillment.

{
    "current_owners": ["<Public Key>"],
    "fid": 0,
    "fulfillment": "cf:4:RxFzIE679tFBk8zwEgizhmTuciAylvTUwy6EL6ehddHFJOhK5F4IjwQ1xLu2oQK9iyRCZJdfWAefZVjTt3DeG5j2exqxpGliOPYseNkRAWEakqJ_UrCwgnj92dnFRAEE",
    "input": {
        "cid": 0,
        "txid": "11b3e7d893cc5fdfcf1a1706809c7def290a3b10b0bef6525d10b024649c42d3"
    }
}

• fid: Fulfillment index. It matches a cid in the conditions with a new crypto condition that the new owner(s) need to fulfill to spend this digital asset
• current_owners: Public key of the current owner(s)
• fulfillment:
• input: Pointer to the digital asset and condition of a previous transaction
  • cid: Condition index
  • txid: Transaction id

The Block Model

{
    "id": "<sha3 hash of the serialized block contents>",
    "block": {
        "timestamp": "<block-creation timestamp>",
        "transactions": ["<list of transactions>"],
        "node_pubkey": "<public key of the node creating the block>",
        "voters": ["<list of federation nodes public keys>"]
    },
    "signature": "<signature of the block>",
    "votes": ["<list of votes>"]
}

Still to be defined when new blocks are created (after x number of transactions, or after x amount of seconds, or both).

A block contains a group of transactions and includes the hash of the hash of the previous block to build the chain.

• id: sha3 hash of the contents of block (i.e. the timestamp, list of transactions, node_pubkey, and voters). This is also a RethinkDB primary key; that's how we ensure that all blocks are unique.
• block: The actual block
  • timestamp: timestamp when the block was created. It's provided by the node that created the block.
  • transactions: the list of transactions included in the block
  • node_pubkey: the public key of the node that create the block
  • voters: list of public keys of the federation nodes. Since the size of the federation may change over time this will tell us how many nodes existed in the federation when the block was created so that at a later point in time we can check that the block received the correct number of votes.
• signature: Signature of the block by the node that created the block (i.e. To create it, the node serialized the block contents and signed that with its private key)
• votes: Initially an empty list. New votes are appended as they come in from the nodes.

The Vote Model

Each node must generate a vote for each block, to be appended to that block's votes list. A vote has the following structure:

{
    "node_pubkey": "<the pubkey of the voting node>",
    "vote": {
        "voting_for_block": "<id of the block the node is voting for>",
        "previous_block": "<id of the block previous to this one>",
        "is_block_valid": "<true|false>",
        "invalid_reason": "<None|DOUBLE_SPEND|TRANSACTIONS_HASH_MISMATCH|NODES_PUBKEYS_MISMATCH",
        "timestamp": "<timestamp of the voting action>"
    },
    "signature": "<signature of vote block>"
}

Note: The invalid_reason was not being used as of v0.1.3.