Random

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The Random ledger object is a singleton that holds the consensus random seed for a ledger, together with the validators’ outstanding commitments for future ledgers. It is written when the ledger is built, by applying the Entropy pseudo-transactions that validators include in their consensus positions. Hooks draw random numbers derived from this seed with the dice and util_random Hook API functions.

Example JSON

The Random object on the Release Candidate devnet at ledger 9224, where all 5 validators on the UNLReport contributed:

{
  "EntropyCount": 5,
  "EntropyDenominator": 5,
  "Flags": 0,
  "LedgerEntryType": "Random",
  "LedgerSequence": 9224,
  "PreviousTxnID": "E4348BFE35489BAE5859C53ED33852C096A8AA85257AAD255CAC1BB1D4779339",
  "PreviousTxnLgrSeq": 9224,
  "RandomData": "82113FC5D6FFE61BD07775031DE166ECBA3D3FC0BA343892B666210CD31C508E",
  "RandomDigests": [
    {
      "RandomDigestEntry": {
        "LedgerSequence": 9224,
        "NextRandomDigest": "624678B11E6565C3D4FD229039D5A8E0F592446794DEDA7EB32522B249207424",
        "PublicKey": "ED21AFD3E309C9605BBAEADEC8D622117E6911A270F05E641CE1CC4E6D8616FCAE"
      }
    },
    {
      "RandomDigestEntry": {
        "LedgerSequence": 9224,
        "NextRandomDigest": "478A2C62384A97961E852D0401F8C3971FC8F5BBB667BEF50505633772675601",
        "PublicKey": "ED54AF10761CF330D0B212A51FA29C094EB213651A74B8E1EF4D128C2CE6141CAF"
      }
    },
    {
      "RandomDigestEntry": {
        "LedgerSequence": 9224,
        "NextRandomDigest": "D5BE872C5DBA4E189E17E781F4E95C8DD786131877C61713749D3514E253982E",
        "PublicKey": "EDA28D7F899E8CEBCE9A4DFE6815843BBE4C338649C03E9B7671F23356B41F41B3"
      }
    },
    {
      "RandomDigestEntry": {
        "LedgerSequence": 9224,
        "NextRandomDigest": "754C777405ACA07DAFD7D6EA855202E543D4F10F71DCBDF6AA04CF4BB4253094",
        "PublicKey": "EDB92F505485DE1B273FB67D6FB1F101AA01BFA0C5F65D67496FE85E912ECB4487"
      }
    },
    {
      "RandomDigestEntry": {
        "LedgerSequence": 9224,
        "NextRandomDigest": "FA7999A7BF6B6D4F5EA52695039D94DDF3DD7D63CAD399F54EFD266B0674642B",
        "PublicKey": "EDE2D7027ABF9ED6C781F32DD8301785A47D356DF15FE839B756E281899149DECE"
      }
    }
  ],
  "index": "125C53F238F6CA65C41A3287F760CCF04F2D0407A8FE016B59F460FE14F0C677"
}

Fields

A Random object has the following fields:

Field	JSON Type	Internal Type	Required?	Description
`LedgerEntryType`	String	UInt16	Yes	The value `0x526E`, mapped to the string `Random`, indicates that this object is a Random object.
`LedgerSequence`	Number	UInt32	Yes	The ledger index that the seed in `RandomData` is for.
`RandomData`	String	Hash256	Yes	The random seed for this ledger, produced by mixing the valid reveals of the contributing validators. This field is never written to ledger-object metadata.
`EntropyCount`	Number	UInt16	Yes	How many validators contributed a valid reveal to this ledger’s seed.
`EntropyDenominator`	Number	UInt16	Yes	How many validators were eligible to contribute (the size of the UNLReport, when one exists).
`RandomDigests`	Array	Array	Yes	An array of `RandomDigestEntry` objects: the outstanding commitments that validators will reveal in a later ledger. See RandomDigestEntry Fields. This field is never written to metadata.
`PreviousTxnID`	String	Hash256	Yes	The identifying hash of the transaction that most recently modified this object.
`PreviousTxnLgrSeq`	Number	UInt32	Yes	The [index of the ledger][Ledger Index] that contains the transaction that most recently modified this object.

RandomDigestEntry Fields

Each member of the RandomDigests array is a RandomDigestEntry inner object with the following fields:

Field	JSON Type	Internal Type	Required?	Description
`PublicKey`	String	Blob	Yes	The master public key of the validator that made the commitment.
`NextRandomDigest`	String	Hash256	Yes	The validator’s commitment (digest) to the secret it will reveal in a later `Entropy` transaction.
`LedgerSequence`	Number	UInt32	Yes	The ledger index in which the commitment was registered.

How the Seed Is Produced

Commit. Each proposing validator on the UNLReport puts exactly one Entropy pseudo-transaction into its own initial consensus position when it closes a ledger. The transaction never enters the open ledger, so its contents only become public once that validator’s transaction set is locked. It contains a commitment (NextRandomDigest) to a new secret and the reveal (RandomData) of the secret it committed to last time.
Reveal and mix. When the ledger is built, all Entropy transactions are applied before any other transaction. A reveal that matches the validator’s stored commitment in RandomDigests is mixed into the seed and counted in EntropyCount. A missing, lost or mismatched reveal just re-registers a new commitment, which has the same effect as the validator withholding.
Expiry. A commitment that is not refreshed within 8 ledgers is dropped from RandomDigests.

Only validators on the UNLReport may contribute, when a UNLReport exists. Validators need no configuration: contribution is automatic once the RNG amendment is enabled.

Use by Hooks

Hooks never read this object directly. The dice and util_random Hook API functions derive their output from the seed, mixing in the transaction ID, Hook account, Hook hash, chain position, strong/weak execution, callback flag and the WebAssembly parameter, so two executions never receive the same output.

A draw only succeeds if at least 80% of the UNLReport contributed to this ledger’s seed (EntropyCount / EntropyDenominator). If there is no UNLReport (new networks, standalone mode), at least one validator must have contributed. Otherwise the draw fails with TOO_LITTLE_ENTROPY (-46).
The Random object is invisible to Hooks: slot_set and ledger_keylet refuse it with DOESNT_EXIST, and it is excluded from provisional metadata.
The validated metadata of any transaction whose Hooks drew random numbers contains a RandomData field holding the RNG state that the transaction’s first draw saw. This includes transactions that fail with tecHOOK_REJECTED; failed draws (for example dice(0)) do not add it. Every value its Hooks received is derived from it, so results can be audited.
While a transaction is applied to the open ledger, draws may use the previous ledger’s seed. The authoritative result is decided when the ledger closes, so a Hook’s outcome in the open ledger may differ from its validated outcome.

Random ID Format

The Random object ID is the SHA-512Half of the Random space key (0x526E) only. This means that the ID of the Random object in a ledger is always:

125C53F238F6CA65C41A3287F760CCF04F2D0407A8FE016B59F460FE14F0C677

Retrieving the Object

Use the ledger_entry method with the random selector:

{
  "command": "ledger_entry",
  "random": true,
  "ledger_index": "validated"
}

random also accepts the object ID as a string. Any other value returns malformedRequest.

Note: The pre-existing random RPC method, which returns a local random number from the node, is unrelated to this object.

Entropy pseudo-transaction: How validators commit and reveal entropy
RNG amendment