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Number Category Status Author Organization Created
0019
Informational
Draft
Xuejie Xiao
Nervos Foundation
2019-03-26

Data Structures of Nervos CKB

This documents explains all the basic data structures used in CKB.

Cell

Example

{
  "capacity": "0x19995d0ccf",
  "lock": {
    "code_hash": "0x9bd7e06f3ecf4be0f2fcd2188b23f1b9fcc88e5d4b65a8637b17723bbda3cce8",
    "args": "0x0a486fb8f6fe60f76f001d6372da41be91172259",
    "hash_type": "type"
  },
  "type": null
}

Description

Name Type Description
capacity uint64 The size of the cell (in shannons). When a new cell is generated (via transaction), one of the verification rule is capacity_in_bytes >= len(capacity) + len(data) + len(type) + len(lock). This value also represents the balance of CKB coin, just like the nValue field in the Bitcoin's CTxOut. (E.g. Alice owns 100 CKB coins means she can unlock a group of cells that has 100 amount of bytes (which is 10_000_000_000 amount of shannons) in total.). The actual value is returned in hex string format.
type Script A Script that defines the type of the cell. It limits how the data field of the new cells can be changed from old cells. type is required to has a data structure of script. This field is optional.
lock Script A Script that defines the ownership of the cell, just like the scriptPubKey field in the Bitcoin's CTxOut. Whoever can provide unlock arguments that makes the execution of this script success can consume this cell as input in an transaction (i.e. has the ownership of this cell).

More information about Cell can be found in the whitepaper.

Script

Example

{
  "code_hash": "0x9bd7e06f3ecf4be0f2fcd2188b23f1b9fcc88e5d4b65a8637b17723bbda3cce8",
  "args": "0x0a486fb8f6fe60f76f001d6372da41be91172259",
  "hash_type": "type"
}

Description

Name Type Description
code_hash H256(hash) The hash of ELF formatted RISC-V binary that contains a CKB script. For space efficiency consideration, the actual script is attached to current transaction as a dep cell. Depending on the value of hash_type, the hash specified here should either match the hash of cell data part in the dep cell, or the hash of type script in the dep cell. The actual binary is loaded into an CKB-VM instance when they are specified upon the transaction verification.
args Bytes The argument as the script input. The argument here is imported into the CKB-VM instance as the input argument for the scripts.
hash_type String, could be type or data The interpretation of code hash when looking for matched dep cells. If this is data, code_hash should match the blake2b hash of data in a dep cell; if this is type, code_hash should instead match the type script hash of a dep cell.

When a script is validated, CKB will run it in a RISC-V VM, args must be loaded via special CKB syscalls. UNIX standard argc/argv convention is not used in CKB. For more information on the CKB VM please refer to CKB VM RFC.

For more information regarding how Script structure is implemented please refer to the CKB repo.

Transaction

Example

{
  "version": "0x0",
  "cell_deps": [
    {
      "out_point": {
        "tx_hash": "0xbd864a269201d7052d4eb3f753f49f7c68b8edc386afc8bb6ef3e15a05facca2",
        "index": "0x0"
      },
      "dep_type": "dep_group"
    }
  ],
  "header_deps": [
    "0xaa1124da6a230435298d83a12dd6c13f7d58caf7853f39cea8aad992ef88a422"
  ],
  "inputs": [
    {
      "previous_output": {
        "tx_hash": "0x8389eba3ae414fb6a3019aa47583e9be36d096c55ab2e00ec49bdb012c24844d",
        "index": "0x1"
      },
      "since": "0x0"
    }
  ],
  "outputs": [
    {
      "capacity": "0x746a528800",
      "lock": {
        "code_hash": "0x9bd7e06f3ecf4be0f2fcd2188b23f1b9fcc88e5d4b65a8637b17723bbda3cce8",
        "args": "0x56008385085341a6ed68decfabb3ba1f3eea7b68",
        "hash_type": "type"
      },
      "type": null
    },
    {
      "capacity": "0x1561d9307e88",
      "lock": {
        "code_hash": "0x9bd7e06f3ecf4be0f2fcd2188b23f1b9fcc88e5d4b65a8637b17723bbda3cce8",
        "args": "0x886d23a7858f12ebf924baaacd774a5e2cf81132",
        "hash_type": "type"
      },
      "type": null
    }
  ],
  "outputs_data": [
    "0x",
    "0x"
  ],
  "witnesses": [
    "0x55000000100000005500000055000000410000004a975e08ff99fa000142ff3b86a836b43884b5b46f91b149f7cc5300e8607e633b7a29c94dc01c6616a12f62e74a1415f57fcc5a00e41ac2d7034e90edf4fdf800"
  ]
}

Description

Transaction

Name Type Description
version uint32 The version of the transaction. It‘s used to distinguish transactions when there's a fork happened to the blockchain system.
cell_deps [CellDep] An array of outpoint pointing to the cells that are dependencies of this transaction. Only live cells can be listed here. The cells listed are read-only.
header_deps [H256(hash)] An array of H256 hashes pointing to block headers that are dependencies of this transaction. Notice maturity rules apply here: a transaction can only reference a header that is at least 4 epochs old.
inputs [CellInput] An array of referenced cell inputs. See below for explanations of underlying data structure
outputs [Cells], see above for details An array of cells that are used as outputs, i.e. the newly generated cells. These are the cells may be used as inputs for other transactions. Each of the Cell has the same structure to the Cell section above.
outputs_data [Bytes] An array of cell data for each cell output. The actual data are kept separated from outputs for the ease of CKB script handling and for the possibility of future optimizations.
witnesses [Bytes] Witnesses provided by transaction creator to make the execution of corresponding lock script success. One example here, is that signatures might be include here to make sure a signature verification lock script passes.

CellDep

Name Type Description
out_point OutPoint A cell outpoint that point to the cells used as deps. Dep cells are dependencies of a transaction, it could be used to include code that are loaded into CKB VM, or data that could be used in script execution.
dep_type String, either code or dep_group The way to interpret referenced cell deps. A cell dep could be referenced in 2 ways: for a cell dep with code as dep_type, the dep cell is directly included in the transaction. If a cell dep dep_type uses dep_group, however, CKB would first load this dep cell, assume the content of this cell contains a list of cell deps, then use the extracted list of cell deps to replace current cell dep, and include them in current transaction. This provides a quicker and smaller(in terms of transaction size) to include multiple commonly used dep cells in one CellDep construct.

CellInput

Name Type Description
previous_output OutPoint A cell outpoint that point to the cells used as inputs. Input cells are in fact the output of previous transactions, hence they are noted as previous_output here. These cells are referred through outpoint, which contains the transaction hash of the previous transaction, as well as this cell's index in its transaction's output list.
since uint64 Since value guarding current referenced inputs. Please refer to the Since RFC for details on this field.

OutPoint

Name Type Description
hash H256(hash) The hash of the transaction that this cell belongs to.
index uint32 The index of the cell in its transaction's output list.

More information about the Transaction of Nervos CKB can be found in whitepaper.

Block

Example

{
  "uncles": [
    {
      "proposals": [

      ],
      "header": {
        "compact_target": "0x1a9c7b1a",
        "hash": "0x87764caf4a0e99302f1382421da1fe2f18382a49eac2d611220056b0854868e3",
        "number": "0x129d3",
        "parent_hash": "0x815ecf2140169b9d283332c7550ce8b6405a120d5c21a7aa99d8a75eb9e77ead",
        "nonce": "0x78b105de64fc38a200000004139b0200",
        "timestamp": "0x16e62df76ed",
        "transactions_root": "0x66ab0046436f97aefefe0549772bf36d96502d14ad736f7f4b1be8274420ca0f",
        "proposals_hash": "0x0000000000000000000000000000000000000000000000000000000000000000",
        "uncles_hash": "0x0000000000000000000000000000000000000000000000000000000000000000",
        "version": "0x0",
        "epoch": "0x7080291000049",
        "dao": "0x7088b3ee3e738900a9c257048aa129002cd43cd745100e000066ac8bd8850d00"
      }
    }
  ],
  "proposals": [
    "0x5b2c8121455362cf70ff"
  ],
  "transactions": [
    {
      "version": "0x0",
      "cell_deps": [

      ],
      "header_deps": [

      ],
      "inputs": [
        {
          "previous_output": {
            "tx_hash": "0x0000000000000000000000000000000000000000000000000000000000000000",
            "index": "0xffffffff"
          },
          "since": "0x129d5"
        }
      ],
      "outputs": [
        {
          "capacity": "0x1996822511",
          "lock": {
            "code_hash": "0x9bd7e06f3ecf4be0f2fcd2188b23f1b9fcc88e5d4b65a8637b17723bbda3cce8",
            "args": "0x2ec3a5fb4098b14f4887555fe58d966cab2c6a63",
            "hash_type": "type"
          },
          "type": null
        }
      ],
      "outputs_data": [
        "0x"
      ],
      "witnesses": [
        "0x590000000c00000055000000490000001000000030000000310000009bd7e06f3ecf4be0f2fcd2188b23f1b9fcc88e5d4b65a8637b17723bbda3cce801140000002ec3a5fb4098b14f4887555fe58d966cab2c6a6300000000"
      ],
      "hash": "0x84395bf085f48de9f8813df8181e33d5a43ab9d92df5c0e77d711e1d47e4746d"
    }
  ],
  "header": {
    "compact_target": "0x1a9c7b1a",
    "hash": "0xf355b7bbb50627aa26839b9f4d65e83648b80c0a65354d78a782744ee7b0d12d",
    "number": "0x129d5",
    "parent_hash": "0x4dd7ae439977f1b01a8c9af7cd4be2d7bccce19fcc65b47559fe34b8f32917bf",
    "nonce": "0x91c4b4746ffb69fe000000809a170200",
    "timestamp": "0x16e62dfdb19",
    "transactions_root": "0x03c72b4c2138309eb46342d4ab7b882271ac4a9a12d2dcd7238095c2d131caa6",
    "proposals_hash": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "uncles_hash": "0x90eb89b87b4af4c391f3f25d0d9f59b8ef946d9627b7e86283c68476fee7328b",
    "version": "0x0",
    "epoch": "0x7080293000049",
    "dao": "0xae6c356c8073890051f05bd38ea12900939dbc2754100e0000a0d962db850d00"
  }
}

Description

Block

Name Type Description
header Header The block header of the block. This part contains some metadata of the block. See the Header section below for the details of this part.
transactions [Transaction] An array of committed transactions contained in the block. Each element of this array has the same structure as the Transaction structure above.
proposals [string] An array of hex-encoded short transaction ID of the proposed transactions.
uncles [UncleBlock] An array of uncle blocks of the block. See the UncleBlock section below for the details of this part.

Header

(header is a sub-structure of block and UncleBlock.)

Name Type Description
compact_target uint32 The difficulty of the PoW puzzle represented in compact target format.
number uint64 The block height.
parent_hash H256(hash) The hash of the parent block.
nonce uint128 The nonce. Similar to the nonce in Bitcoin. Represent the solution of the PoW puzzle
timestamp uint64 A Unix time timestamp in milliseconds.
transactions_root H256(hash) The hash of concatenated transaction hashes CBMT root and transaction witness hashes CBMT root.
proposals_hash H256(hash) The hash of concatenated proposal ids. (all zeros when proposals is empty)
uncles_hash H256(hash) The hash of concatenated hashes of uncle block headers. (all zeros when uncles is empty)
version uint32 The version of the block. This is for solving the compatibility issues might be occurred after a fork.
epoch uint64 Current epoch information. Assume number represents the current epoch number, index represents the index of the block in the current epoch(start at 0), length represents the length of current epoch. The value store here will then be (number & 0xFFFFFF) | ((index & 0xFFFF) << 24) | ((length & 0xFFFF) << 40)
dao Bytes Data containing DAO related information. Please refer to Nervos DAO RFC for details on this field.

UncleBlock

(UncleBlock is a sub-structure of Block.)

Name Type Description
header Header The block header of the uncle block. The inner structure of this part is same as the Header structure above.
proposals [string] An array of short transaction IDs of the proposed transactions in the uncle block.