> For the complete documentation index, see [llms.txt](https://docs.ltonetwork.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.ltonetwork.com/protocol/public/data-structures.md). # Data Structures ## Blockchain Objects ### Signed transaction #### Version 1 and 2 | Field Name | Type | Length | | :--------------------------: | :----------------------: | ------ | | Transaction type | Byte | 1 | | Version | Byte | 1 | | *Transaction specific bytes* | | | | Proofs version | Byte (constant, value=1) | 1 | | Proof size (N) | Short | 2 | | Proof | Array\[Byte] | N | #### Version 3+ | Field Name | Type | Length | | :--------------------------: | :----------------------: | ------------- | | Transaction type | Byte | 1 | | Version | Byte | 1 | | Timestamp | Long | 8 | | Sender's key type | KeyType (Byte) | 1 | | Sender's public key | PublicKey (Array\[Byte]) | 32 \| 33 | | Fee | Long | 8 | | *Transaction specific bytes* | | | | Sponsor's key type | KeyType (Byte) | 1 | | Sponsor's public key | PublicKey (Array\[Byte]) | 0 \| 32 \| 33 | | Proofs version | Byte (constant, value=1) | 1 | | Proof size (N) | Short | 2 | | Proof | Array\[Byte] | N | {% hint style="info" %} In version 3+ more fields are standardized. These are part of the transaction-specific bytes in versions 1 and 2. {% endhint %} ### Block | Field Name | Type | Length | | :-----------------------------------------------------: | :---: | ------ | | Version (0x02 for Genesis block, 0x03 for common block) | Byte | 0 | | Timestamp | Long | 1 | | Parent block signature | Bytes | 64 | | Consensus block length (always 40 bytes) | Int | 4 | | Base target | Long | 8 | | Generation signature\* | Bytes | 32 | | Transactions block length (N) | Int | 8 | | Transaction #1 bytes | Bytes | M1 | | ... | ... | ... | | Transaction #K bytes | Bytes | MK | | Generator's public key | Bytes | 32 | | Block's signature | Bytes | 64 | Generation signature is calculated as `blake2b256` hash of the following bytes: | Field Name | Type | Length | | :-----------------------------------: | :---: | ------ | | Previous block's generation signature | Bytes | 32 | | Generator's public key | Bytes | 32 | Block's signature is calculated from the following bytes: | Field Name | Type | Length | | :-----------------------------------------------------: | :---: | ------ | | Version (0x02 for Genesis block, 0x03 for common block) | Byte | 0 | | Timestamp | Long | 1 | | Parent block signature | Bytes | 64 | | Consensus block length (always 40 bytes) | Int | 4 | | Base target | Long | 8 | | Generation signature\* | Bytes | 32 | | Transactions block length (N) | Int | 8 | | Transaction #1 bytes | Bytes | M1 | | ... | ... | ... | | Transaction #K bytes | Bytes | MK | | Generator's public key | Bytes | 32 | ## Network messages ### Network message structure All network messages share the same structure, except the Handshake. | Field name | Type | Length | | :-----------------------: | :---: | ------ | | Packet length (BigEndian) | Int | 4 | | Magic Bytes | Bytes | 4 | | Content ID | Byte | 1 | | Payload length | Int | 4 | | Payload checksum | Bytes | 4 | | Payload | Bytes | N | Magic Bytes are `0x12 0x34 0x56 0x78`. Payload checksum is the first 4 bytes of *FastHash* of Payload bytes. *FastHash* is the hash function `Blake2b256(data)`. ### Handshake message Handshake is used to start communication between two nodes. | Field name | Type | Length | | :-------------------------------------------------------------: | :---: | ------ | | Application name length (N) | Byte | 1 | | Application name (UTF-8 encoded bytes) | Bytes | N | | Application version major | Int | 4 | | Application version minor | Int | 4 | | Application version patch | Int | 4 | | Node name length (M) | Byte | 1 | | Node name (UTF-8 encoded bytes) | Bytes | M | | Node nonce | Long | 8 | | Declared address length (K) or 0 if no declared address was set | Int | 4 | | Declared address bytes (if length is not 0) | Bytes | K | | Timestamp | Long | 8 | ### GetPeers message GetPeers message is sent when sending node wants to know of other nodes on network. | Field name | Type | Length | | :-----------------------: | :---: | ------ | | Packet length (BigEndian) | Int | 4 | | Magic Bytes | Bytes | 4 | | Content ID (0x01) | Byte | 1 | | Payload length | Int | 4 | | Payload checksum | Bytes | 4 | ### Peers message Peers message is a reply on GetPeers message. | Field name | Type | Length | | :-----------------------: | :---: | ------ | | Packet length (BigEndian) | Int | 4 | | Magic Bytes | Bytes | 4 | | Content ID (0x02) | Byte | 1 | | Payload length | Int | 4 | | Payload checksum | Bytes | 4 | | Peers count (N) | Int | 4 | | Peer #1 IP address | Bytes | 4 | | Peer #1 port | Int | 4 | | ... | ... | ... | | Peer #N IP address | Bytes | 4 | | Peer #N port | Int | 4 | ### GetSignatures message | Field name | Type | Length | | :-----------------------: | :---: | ------ | | Packet length (BigEndian) | Int | 4 | | Magic Bytes | Bytes | 4 | | Content ID (0x14) | Byte | 1 | | Payload length | Int | 4 | | Payload checksum | Bytes | 4 | | Block IDs count (N) | Int | 4 | | Block #1 ID | Bytes | 64 | | ... | ... | ... | | Block #N ID | Bytes | 64 | ### Signatures message | Field name | Type | Length | | :------------------------: | :---: | ------ | | Packet length (BigEndian) | Int | 4 | | Magic Bytes | Bytes | 4 | | Content ID (0x15) | Byte | 1 | | Payload length | Int | 4 | | Payload checksum | Bytes | 4 | | Block signatures count (N) | Int | 4 | | Block #1 signature | Bytes | 64 | | ... | ... | ... | | Block #N signature | Bytes | 64 | ### GetBlock message | Field name | Type | Length | | :-----------------------: | :---: | ------ | | Packet length (BigEndian) | Int | 4 | | Magic Bytes | Bytes | 4 | | Content ID (0x16) | Byte | 1 | | Payload length | Int | 4 | | Payload checksum | Bytes | 4 | | Block ID | Bytes | 64 | ### Block message | Field name | Type | Length | | :-----------------------: | :---: | ------ | | Packet length (BigEndian) | Int | 4 | | Magic Bytes | Bytes | 4 | | Content ID (0x17) | Byte | 1 | | Payload length | Int | 4 | | Payload checksum | Bytes | 4 | | Block bytes (N) | Bytes | N | ### Score message | Field name | Type | Length | | :-----------------------: | :----: | ------ | | Packet length (BigEndian) | Int | 4 | | Magic Bytes | Bytes | 4 | | Content ID (0x18) | Byte | 1 | | Payload length | Int | 4 | | Payload checksum | Bytes | 4 | | Score (N bytes) | BigInt | N | ### Transaction message | Field name | Type | Length | | :-----------------------: | :---: | ------ | | Packet length (BigEndian) | Int | 4 | | Magic Bytes | Bytes | 4 | | Content ID (0x19) | Byte | 1 | | Payload length | Int | 4 | | Payload checksum | Bytes | 4 | | Transaction (N bytes) | Bytes | N | ### Checkpoint message | Field name | Type | Length | | :------------------------: | :---: | ------ | | Packet length (BigEndian) | Int | 4 | | Magic Bytes | Bytes | 4 | | Content ID (0x64) | Byte | 1 | | Payload length | Int | 4 | | Payload checksum | Bytes | 4 | | Checkpoint items count (N) | Int | 4 | | Checkpoint #1 height | Long | 8 | | Checkpoint #1 signature | Bytes | 64 | | ... | ... | ... | | Checkpoint #N height | Long | 8 | | Checkpoint #N signature | Bytes | 64 |