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anchor.md

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description
Anchoring stores a hash on the blockchain, allowing anyone to verify that data hasn't been tempered with.

Anchor

JSON

{
  "type": 15,
  "version": 3,
  "id": "8M6dgn85eh3bsHrVhWng8FNaHBcHEJD4MPZ5ZzCciyon",
  "sender": "3Jq8mnhRquuXCiFUwTLZFVSzmQt3Fu6F7HQ",
  "senderKeyType": "ed25519",
  "senderPublicKey": "AJVNfYjTvDD2GWKPejHbKPLxdvwXjAnhJzo6KCv17nne",
  "fee": 35000000,
  "timestamp": 1610397549043,
  "anchors": [
    "5SbkwAekNbaG8P1mTDdAE88mpWtCdET9vTmV2v9vQsCK",
    ...
  ],
  "proofs": [
    "4aMwABCZwtXrGGKmBdHdR5VVFqG51v5dPoyfDVZ7jfgD3jqc851ME5QkToQdfSRTqQmvnB9YT4tCBPcMzi59fZye"
  ],
  "height": 1069662
}

{% hint style="info" %}

  • id and height should be omitted when broadcasting. These fields are set by the node.
  • Binary strings are base58 encoded.
  • timestamp is in microseconds since epoch.
  • fee includes 8 digits, so LTO * 10^8 {% endhint %}

Batch transaction

Up to 100 hashes can be anchored in a single transaction. Bundling multiple anchors in 1 transaction can help reduce transaction fees.

The Anchor fee is made up of two amounts: a fixed one plus a per-anchor one. The fees are calculated as:

0.25 + 0.1 * N

where N is the number of anchor hashes in the transaction. The total is rounded up to the nearest 100_000.

Binary schema

The binary data structure of the unsigned transaction.

{% tabs %} {% tab title="V3 (current)" %}

# Field Name Type Length
1 Transaction type Byte (constant, value=15) 1
2 Version Byte (constant, value=3) 1
3 Network id Byte 1
4 Timestamp Long 8
5 Sender's key type KeyType (Byte) 1
6 Sender's public key PublicKey (Array[Byte]) 32 | 33
7 Fee Long 8
8 Number of anchors Short 2
9 Anchor 1 length (N) Byte 2
10 Anchor 1 Array[Byte] N
...

{% hint style="info" %}

  • Anchor length and Anchor are repeated for each anchor hash.
  • The maximum length of an anchor is 100 bytes.
  • Network id can be obtained by taking the 2nd byte from the sender address.
  • Each key type has a numeric id in addition to the reference from the JSON.
  • Integers (short, int, long) have a big endian byte order. {% endhint %} {% endtab %}

{% tab title="V1" %}

# Field Name Type Length
1 Transaction type Byte (constant, value=15) 1
2 Version Byte (constant, value=1) 1
3 Sender's public key PublicKey (Array[Byte]) 32
4 Number of anchors Short (constant, value=1) 2
5 Anchor 1 length (N) Short 2
6 Anchor 1 Array[Byte] N
...
7 Timestamp Long 8
8 Fee Long 8

{% hint style="info" %}

  • Anchor length and Anchor can be repeated for each anchor hash.
  • Integers (short, int, long) have a big endian byte order. {% endhint %} {% endtab %} {% endtabs %}