Serialization standard

There is a custom implementation to serialize data structures used by the Casper Node to their byte representation. This document details and describes the way in which this custom serialization is implemented, allowing developers to build their own library that implements the custom serialization.


A proto-block after execution, with the resulting post-state-hash. This is the core component of the Casper linear blockchain. The defintions and serialization for a ProtoBlock are defined below. A block is programmtically defined as follows

pub struct Block {
    hash: BlockHash,
    header: BlockHeader,
    body: (),
    proofs: Vec<Signature>,
  • hash: A hash over the body of the Block.

  • header: The header of the block which contains information about the contents of the block with additional metadata.

  • body: Currently empty

  • proofs: An array/vector of signatures over the Block.

Block hash

The blockhash is a Digest over the contents of the Block Header. The BlockHash serialises as the byte representation of the hash itself.

Block header

The header portion of a Block, programmtically, it is defined as follows:

pub struct BlockHeader {
    parent_hash: BlockHash,
    state_root_hash: Digest,
    body_hash: Digest,
    deploy_hashes: Vec<DeployHash>,
    random_bit: bool,
    accumulated_seed: Digest,
    era_end: Option<EraEnd>,
    timestamp: Timestamp,
    era_id: EraId,
    height: u64,
    proposer: PublicKey,
  • parent_hash: is the hash of the parent block

  • state_root_hash: is the current State Root hash

  • body_hash: is the serialized representation of a unit type, (), its serialization is described below

  • deploy_hashes: is a vector of hex-encoded hashes identifying Deploys included in this Block

  • random_bit: is a boolean whose serialization is desribed below

  • accumulated_seed: A seed needed for initializing a future era.

  • era_end: contains Equivocation and reward information to be included in the terminal finalized block.

  • timestamp: The timestamp from when the proto block was proposed.

  • era_id: Era ID in which this block was created.

  • height: The height of this block, i.e. the number of ancestors.

  • proposer: The PublicKey which proposed this block.

When serializing the BlockHeader, we create a buffer which contains the serialized representations of each of the header fields.

  • parent_hash serializes to the byte representation of the parent hash. The serialized buffer of the parent_hash is 32 bytes long.

  • state_root_hash serializes to the byte representation of the state root hash. The serialized buffer of the state_root_hash is 32 bytes long.

  • body_hash is the serialized representation of the unit type (). Its serialization is described in detail in the CLValue section.

  • deploy_hashes serialises to the byte representation of all the deploy_hashes within the block header. Its length is `32 * n, where n denotes the amount of deploy hashes present within the header.

  • random_bit is serialized as a single byte; true maps to 1, while false maps to 0.

  • accumulated_seed serializes to the byte representation of the parent Hash. The serialized buffer of the accumulated_hash is 32 bytes long.

  • era_end is an optional field. Thus if the field is set as None it serialises to 0. The serialization of the other case is described in the follow section.

  • timestamp serialises as a single u64 value. The serialization of a u64 value is desribed in its own section, below.

  • era_id serialises as a single u64 value. The serialization of a u64 value is desribed in its own section, below.

  • proposer serialises to the byte representation of the PublicKey. If the PublicKey is an Ed25519 key, then the first byte within the serialized buffer is 1 followed by the bytes of the key itself, else, in the case of Secp256k1, the first byte is 2.


EraEnd as represented within the block header is a struct containing two fields.

  • equivocatiors: A vector of PublicKey.

  • rewards: A Binary Tree Map of PublicKey and u64.

When serializing an EraEnd, the buffer is first filled with the indiviual serialization of the PublicKey’s contained within the vector.

  • If the PublicKey is an Ed25519 key, the first byte within the buffer is a 1 followed by the indiviual bytes of the serialized key.

  • If the PublicKey is an Secp256k1 key, the first byte within the buffer is a 2 followed by the indiviual bytes of the serialized key.


The Body of the Block is an empty field and NOT included in the serialization of the block. It should be noted that the Header contains a hash over the empty (), but the actual serialized block does not.


Proofs is a field within the block which contains a vector of Signature’s over the Block.

  • If the Signature is of the Ed25519 variant, then the serialized buffer contains 1 as the first byte, followed by the byte representation of the signature.

  • If the Signature is of the Secp256k1 variant, then the serialised buffer contains 2 as the first byte, followed by the byte representation of the signature,

Eg: In the case of Ed25519:

  • 4a249f895c01a2a12fbf4f613d071ff00883711612d66a18f27cec9d543fd18777b4e6f94eae3c8c9ee0b5b19ce886d255be5fcaf826f5b49ddf50e1df550809

will serialize to

  • 014a249f895c01a2a12fbf4f613d071ff00883711612d66a18f27cec9d543fd18777b4e6f94eae3c8c9ee0b5b19ce886d255be5fcaf826f5b49ddf50e1df550809

In the case of Secp256k1:

  • 0392ded56f5f0b8c78b7da2fa24c14fbede711a287360a9502e356750ef156d03ea32ab3260e8ea5dcc9093831e1e0dce253c277db9dad07505283e2c2895d83

will serialize to

  • 020392ded56f5f0b8c78b7da2fa24c14fbede711a287360a9502e356750ef156d03ea32ab3260e8ea5dcc9093831e1e0dce253c277db9dad07505283e2c2895d83

High Level View

Thus, considering the information a block:

Block {
    hash: BlockHash(
    header: BlockHeader {
        parent_hash: BlockHash(
        state_root_hash: 7d65cb919feb758f17c55a51b1cec92d88a34505488208d4f3a79486baf1f6c2,
        body_hash: 0e5751c026e543b2e8ab2eb06099daa1d1e5df47778f7787faab45cdf12fe3a8,
        deploy_hashes: [
        random_bit: false,
        accumulated_seed: cff903daf62d5c301fd0960e26eab14a0aa500d832539c3db88fecf90fbe69a2,
        era_end: None,
        timestamp: Timestamp(
        era_id: EraId(
        height: 32,
        proposer: PublicKey::Ed25519(7fdb6db5c5386a89e349085e167805c075cca3e063a27d6b9df9b8bf5d001757),
    body: (),
    proofs: [

will serialize to:



A deploy is a data structure containing a smart contract along with the requester’s signature(s). Additionally, the deploy header contains additional metadata about the deploy itself. A deploy is programmtically defined as follows

pub struct Deploy {
    hash: DeployHash,
    header: DeployHeader,
    payment: ExecutableDeployItem,
    session: ExecutableDeployItem,
    approvals: Vec<Approval>,
    is_valid: Option<bool>,
  • Hash: The hash of the deploy header.

  • Header: Contains metadata about the deploy. The structure of the header is detailed further in this document.

  • Payment: The payment code for contained smart contract.

  • Session: The stored contract itself.

  • Approvals: A list of signatures:

  • is_valid: A flag that marks the validity of the deploy. Do note that is the only field within the struct that is not serialized.


The Deploy hash is a Digest over the contents of the Deploy header. The Deploy Hash serialises as the byte representation of the hash itself.


The deploy header is defined as

pub struct DeployHeader {
    account: PublicKey,
    timestamp: Timestamp,
    ttl: TimeDiff,
    gas_price: u64,
    body_hash: Digest,
    dependencies: Vec<DeployHash>,
    chain_name: String,
  • Account is defined as enum which can either contain an Ed25519 key or secp256k1 key.

  • An Ed25519 key is serialized as buffer of bytes with the leading byte being 1 for Ed25519

  • Thus an Ed25519 key 4dd8edb64cad4bd472f2ab8b0409392306c14b45f5b47ac0c295da461d09b18a serializes to 0x01200000004dd8edb64cad4bd472f2ab8b0409392306c14b45f5b47ac0c295da461d09b18a

  • Correspondingly a Secp256k1 key is serialized as a buffer of bytes with the leading byte being 2

  • Thus an Secp256k1 key 0365dc07a060cac57c98cdeab9a659e097458d4e72899b4bec4f1b230d57a70d72 serializes as 0x02210000000365dc07a060cac57c98cdeab9a659e097458d4e72899b4bec4f1b230d57a70d72

  • A timestamp is struct that is unary tuple containing a u64 value. This value is a count of the milliseconds since the UNIX epoch. Thus the value 1603994401469 serializes as 0xbd3a847575010000

  • The gas is u64 value which is serialized as u64 CLValue discussed below.

  • Body hash is a hash over the contents of the deploy body which includes the payment, session and approval fields. Its serialization is the byte representation of the hash itself.

  • Dependencies is a vector of deploy hashes referencing deploys that must execute before the current deploy can be executed. It serializes as a buffer containing the indiviual serialization of each DeployHash within the Vector.

  • Chain name is a human readable string describing the name of the chain as detailed in the chainspec. It is serialized as a String CLValue described below.

Payment & Session

Payment and Session are both defined as ExecutableDeployItems. ExecutableDeployItems is an enum described as follows

pub enum ExecutableDeployItem {
    ModuleBytes {
        #[serde(with = "HexForm::<Vec<u8>>")]
        module_bytes: Vec<u8>,
        // assumes implicit `call` noarg entrypoint
        #[serde(with = "HexForm::<Vec<u8>>")]
        args: Vec<u8>,
    StoredContractByHash {
        #[serde(with = "HexForm::<[u8; KEY_HASH_LENGTH]>")]
        hash: ContractHash,
        entry_point: String,
        #[serde(with = "HexForm::<Vec<u8>>")]
        args: Vec<u8>,
    StoredContractByName {
        name: String,
        entry_point: String,
        #[serde(with = "HexForm::<Vec<u8>>")]
        args: Vec<u8>,
    StoredVersionedContractByHash {
        #[serde(with = "HexForm::<[u8; KEY_HASH_LENGTH]>")]
        hash: ContractPackageHash,
        version: Option<ContractVersion>, // defaults to highest enabled version
        entry_point: String,
        #[serde(with = "HexForm::<Vec<u8>>")]
        args: Vec<u8>,
    StoredVersionedContractByName {
        name: String,
        version: Option<ContractVersion>, // defaults to highest enabled version
        entry_point: String,
        #[serde(with = "HexForm::<Vec<u8>>")]
        args: Vec<u8>,
    Transfer {
        #[serde(with = "HexForm::<Vec<u8>>")]
        args: Vec<u8>,
  • Module Bytes are serialized such that the first byte within the serialized buffer is 0 with the rest of the buffer containing the bytes present.
    • ModuleBytes { module_bytes: "[72 bytes]", args: 434705a38470ec2b008bb693426f47f330802f3bd63588ee275e943407649d3bab1898897ab0400d7fa09fe02ab7b7e8ea443d28069ca557e206916515a7e21d15e5be5eb46235f5 } will serialize to

    • 0x0048000000420481b0d5a665c8a7678398103d4333c684461a71e9ee2a13f6e859fb6cd419ed5f8876fc6c3e12dce4385acc777edf42dcf8d8d844bf6a704e5b2446750559911a4a328d649ddd48000000434705a38470ec2b008bb693426f47f330802f3bd63588ee275e943407649d3bab1898897ab0400d7fa09fe02ab7b7e8ea443d28069ca557e206916515a7e21d15e5be5eb46235f5

  • StoredContractByHash serializes such that the first byte within the serialized buffer is 1u8. This is followed by the byte representation of the remain fields.
    • StoredContractByHash { hash: c4c411864f7b717c27839e56f6f1ebe5da3f35ec0043f437324325d65a22afa4, entry_point: "pclphXwfYmCmdITj8hnh", args: d8b59728274edd2334ea328b3292ed15eaf9134f9a00dce31a87d9050570fb0267a4002c85f3a8384d2502733b2e46f44981df85fed5e4854200bbca313e3bca8d888a84a76a1c5b1b3d236a12401a2999d3cad003c9b9d98c92ab1850 }

    • 0x01c4c411864f7b717c27839e56f6f1ebe5da3f35ec0043f437324325d65a22afa41400000070636c7068587766596d436d6449546a38686e685d000000d8b59728274edd2334ea328b3292ed15eaf9134f9a00dce31a87d9050570fb0267a4002c85f3a8384d2502733b2e46f44981df85fed5e4854200bbca313e3bca8d888a84a76a1c5b1b3d236a12401a2999d3cad003c9b9d98c92ab1850

  • StoredContractByName serializes such that the first byte within the serialized buffer is 2u8. This followed by the indiviual byte representation of the remaining fields.
    • StoredContractByName { name: "U5A74bSZH8abT8HqVaK9", entry_point: "gIetSxltnRDvMhWdxTqQ", args: 07beadc3da884faa17454a }

    • 0x0214000000553541373462535a483861625438487156614b39140000006749657453786c746e5244764d685764785471510b00000007beadc3da884faa17454a

  • StoredVersionedContractByHash serializes such that the first byte within the serialized buffer is 3u8. However, the field version within the enum serializes as a Option CLValue, i.e if the value is None as shown in the example, it serializes to 0, else it serialises the inner u32 value which is described below.
    • StoredVersionedContractByHash { hash: b348fdd0d0b3f66468687df93141b5924f6bb957d5893c08b60d5a78d0b9a423, version: None, entry_point: "PsLz5c7JsqT8BK8ll0kF", args: 3d0d7f193f70740386cb78b383e2e30c4f976cf3fa834bafbda4ed9dbfeb52ce1777817e8ed8868cfac6462b7cd31028aa5a7a60066db35371a2f8 }

    • 0x03b348fdd0d0b3f66468687df93141b5924f6bb957d5893c08b60d5a78d0b9a423001400000050734c7a3563374a73715438424b386c6c306b463b0000003d0d7f193f70740386cb78b383e2e30c4f976cf3fa834bafbda4ed9dbfeb52ce1777817e8ed8868cfac6462b7cd31028aa5a7a60066db35371a2f8

  • StoredVersionedContractByName serializes such that the first byte within the serialized buffer is 4u8. The name and entry_point are serialised as a String CLValue, with the Option version field serializing to 0 if the value is None, else it serialises the inner u32 value as described below.
    • StoredVersionedContractByName { name: "lWJWKdZUEudSakJzw1tn", version: Some(1632552656), entry_point: "S1cXRT3E1jyFlWBAIVQ8", args: 9975e6957ea6b07176c7d8471478fb28df9f02a61689ef58234b1a3cffaebf9f303e3ef60ae0d8 }

    • 0x04140000006c574a574b645a5545756453616b4a7a7731746e01d0c64e61140000005331635852543345316a79466c57424149565138270000009975e6957ea6b07176c7d8471478fb28df9f02a61689ef58234b1a3cffaebf9f303e3ef60ae0d8

  • Transfer serialises such that the first byte within the serialised buffer contains is 5u8, with the remaining bytes of the buffer containing the bytes contained within the args field of Transfer.


This is the only field within the Deploy which is not serialized.

Deploy Serialization at High Level

A deploy as described below

"hash": "2640413b0a9f9179d6ae0c7424335483682a4a240a71b0e438be07796c68548b",
"header": {
    "account": "018e8560906e20ac3059fbc0498a86a9f775d51d54c0b36d00c830c4e29a6587f7",
    "timestamp": "2020-10-29T15:28:44.620Z",
    "ttl": "22m 6s 290ms",
    "gas_price": 83,
    "body_hash": "cf0e5d669745d5acea0abb8ee784ee55adf26afc3a3f2e9b8523115a65de679a",
    "dependencies": [
    "chain_name": "casper-example"
"payment": {
    "ModuleBytes": {
    "module_bytes": "9babcba5d0afbe3f06c2adbd907e61f179fb",
    "args": "831728a0fe7862148d71cb5dc812c89c01965d1849"
"session": {
    "Transfer": {
    "args": "9d836ba4cc5b272c362ecdf4c70e1bed0401bbb8bcee18c7ca13945e8f73"
"approvals": [
    "signer": "018e8560906e20ac3059fbc0498a86a9f775d51d54c0b36d00c830c4e29a6587f7",
    "signature": "01fb9a66c5ad0fe86bc5c5afb98dad6f1dde1b82af7ca7522866b558ccc516b020ce2e5d6728c760c72bd5b7c2c5b9c62cc4f0743edd3ac519679342fc5f7d2c03"

will Serialize to 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


A value stored in the global state is a StoredValue. A StoredValue is one of three possible variants:

  • A CLValue

  • A contract

  • An account

We discuss CLValue and contract in more detail below, details about accounts can be found in Accounts.

Each StoredValue is serialized when written to the global state. The serialization format consists of a single byte tag, indicating which variant of StoredValue it is, followed by the serialization of that variant. The tag for each variant is as follows:

  • CLValue is 0

  • Account is 1

  • Contract is 2

The details of CLType serialization is in the following section. Using the serialization format for CLValue as a basis, we can succinctly write the serialization rules for contracts and accounts:

  • contracts serialize in the same way as data with CLType equal to Tuple3(List(U8), Map(String, Key), Tuple3(U32, U32, U32));

  • accounts serialize in the same way as data with CLType equal to Tuple5(FixedList(U8, 32), Map(String, Key), URef, Map(FixedList(U8, 32), U8), Tuple2(U8, U8)).

Note: Tuple5 is not a presently supported CLType, however it is clear how to generalize the rules for Tuple1, Tuple2, Tuple3 to any size tuple.

Note: links to further serialization examples and a reference implementation are found in Appendix B.


CLValue is used to describe data that is used by smart contracts. This could be as a local state variable, input argument or return value. A CLValue consists of two parts: a CLType describing the type of the value, and an array of bytes which represent the data in our serialization format.

CLType is described by the following recursive data type:

enum CLType {
   Bool, // boolean primitive
   I32, // signed 32-bit integer primitive
   I64, // signed 64-bit integer primitive
   U8, // unsigned 8-bit integer primitive
   U32, // unsigned 32-bit integer primitive
   U64, // unsigned 64-bit integer primitive
   U128, // unsigned 128-bit integer primitive
   U256, // unsigned 256-bit integer primitive
   U512, // unsigned 512-bit integer primitive
   Unit, // singleton value without additional semantics
   String, // e.g. "Hello, World!"
   URef, // unforgable reference (see above)
   Key, // global state key (see above)
   Option(CLType), // optional value of the given type
   List(CLType), // list of values of the given type (e.g. Vec in rust)
   FixedList(CLType, u32), // same as `List` above, but number of elements
                           // is statically known (e.g. arrays in rust)
   Result(CLType, CLType), // co-product of the the given types;
                           // one variant meaning success, the other failure
   Map(CLType, CLType), // key-value association where keys and values have the given types
   Tuple1(CLType), // single value of the given type
   Tuple2(CLType, CLType), // pair consisting of elements of the given types
   Tuple3(CLType, CLType, CLType), // triple consisting of elements of the given types
   Any // Indicates the type is not known

All data which can be assigned a (non-Any) CLType can be serialized according to the following rules (this defines the CasperLabs serialization format):

  • Boolean values serialize as a single byte; true maps to 1, while false maps to 0.

  • Numeric values consisting of 64 bits or less serialize in the two’s complement representation with little-endian byte order, and the appropriate number of bytes for the bit-width.

    • E.g. 7u8 serializes as 0x07

    • E.g. 7u32 serializes as 0x07000000

    • E.g. 1024u32 serializes as 0x00040000

  • Wider numeric values (i.e. U128, U256, U512) serialize as: one byte given the length of the subsequent number (in bytes), followed by the two’s complement representation with little-endian byte order. The number of bytes should be chosen as small as possible to represent the given number. This is done to reduce the size of the serialization in the case of small numbers represented within a wide data type.

    • E.g. U512::from(7) serializes as 0x0107

    • E.g. U512::from(1024) serializes as 0x020004

    • E.g. U512::from("123456789101112131415") serializes as 0x0957ff1ada959f4eb106

  • Unit serializes to an empty byte array.

  • Strings serialize as a 32-bit integer representing the length in bytes (note: this might be different than the number of characters since special characters, such as emojis, take more than one byte), followed by the UTF-8 encoding of the characters in the string.

    • E.g. "Hello, World!" serializes as 0x0d00000048656c6c6f2c20576f726c6421

  • Optional values serialize with a single byte tag, followed by the serialization of the value it self. The tag is equal to 0 if the value is missing, and 1 if it is present.

    • E.g. None serializes as 0x00

    • E.g. Some(10u32) serializes as 0x010a000000

  • A list of values serializes as a 32-bit integer representing the number of elements in the list (note this differs from strings where it gives the number of bytes), followed by the concatenation of each serialized element.

    • E.g. List() serializes as 0x00000000

    • E.g. List(1u32, 2u32, 3u32) serializes as 0x03000000010000000200000003000000

  • A fixed-length list of values serializes as simply the concatenation of the serialized elements. Unlike a variable-length list, the length is not included in the serialization because it is statically known by the type of the value.

    • E.g. [1u32, 2u32, 3u32] serializes as 0x010000000200000003000000

  • A Result serializes as a single byte tag followed by the serialization of the contained value. The tag is equal to 1 for the success variant and 0 for the error variant.

    • E.g. Ok(314u64) serializes as 0x013a01000000000000

    • E.g. Err("Uh oh") serializes as 0x00050000005568206f68

  • Tuples serialize as the concatenation of their serialized elements. Similar to FixedList the number of elements is not included in the serialization because it is statically known in the type.

    • E.g. (1u32, "Hello, World!", true) serializes as 0x010000000d00000048656c6c6f2c20576f726c642101

  • A Map serializes as a list of key-value tuples. There must be a well-defined ordering on the keys, and in the serialization the pairs are listed in ascending order. This is done to ensure determinism in the serialization, as Map data structures can be unordered.

  • URef values serialize as the concatenation of its address (which is a fixed-length list of u8) and a single byte tag representing the access rights. Access rights are converted as follows:

Access Rights


















  • Key values serialize as a single byte tag representing the variant, followed by the serialization of the data that variant contains. For most variants this is simply a fixed-length 32 byte array. The exception is Key::URef which contains a URef, so its data serializes per the description above. The tags are as follows: Key::Account serializes as 0, Key::Hash as 1, Key::URef as 2.

CLType itself also has rules for serialization. A CLType serializes as a single byte tag, followed by the concatenation of serialized inner types, if any (e.g. lists, and tuples have inner types). FixedList is a minor exception because it also includes the length in the type, however this simply means that the length included in the serialization as well (as a 32-bit integer, per the serialization rules above), following the serialization of the inner type. The tags are as follows:


Serialization Tag













































A complete CLValue, including both the data and the type can also be serialized (in order to store it in the global state). This is done by concatenating: the serialization of the length (as a 32-bit integer) of the serialized data (in bytes), the serialized data itself, and the serialization of the type.


Contracts are a special value type because they contain the on-chain logic of the applications running on the CasperLabs system. A contract contains the following data:

  • a wasm module

  • a collection of named keys

  • a protocol version

The wasm module must contain a function named call which takes no arguments and returns no values. This is the main entry point into the contract. Moreover, the module may import any of the functions supported by the CasperLabs runtime; a list of all supported functions can be found in Appendix A.

Note: though the call function signature has no arguments and no return value, within the call function body the get_named_arg runtime function can be used to accept arguments (by ordinal) and the ret runtime function can be used to return a single CLValue to the caller.

The named keys are used to give human-readable names to keys in the global state which are important to the contract. For example, the hash key of another contract it frequently calls may be stored under a meaningful name. It is also used to store the URefs which are known to the contract (see below section on Permissions for details).

The protocol version says which version of the CasperLabs protocol this contract was compiled to be compatible with. Contracts which are not compatible with the active major protocol version will not be executed by any node in the CasperLabs network.