Data Serialization

Data serialization is the process of converting data into a format that can be easily stored or transmitted over a network. It typically involves encoding data into a sequence of bytes, which can later be decoded to reconstruct the original data structure. Pactus has two methods for data serialization: Deterministic serialization and CBOR serialization:

Deterministic Serialization

Pactus uses a deterministic serialization for the deterministic data like blocks and transactions. The serialization format for different types of data is listed in the table below:

Data TypeSize (bytes)Description
uint81An 8 bits unsigned integer
int81An 8 bits signed integer
uint162A 16 bits unsigned integer
int162A 16 bits signed integer
uint324A 32 bits unsigned integer
int324A 32 bits signed signed integer
uint648A 64 bits unsigned integer
int648A 64 bits signed signed integer
VarIntVariableA compact representation of an unsigned integer.
VarByteVariableA variable length bytes
VarStringVariableA variable length string
Address2121 bytes of address data
Hash323232 bytes of hash data


Variable length integer (VarInt) is encoded by 7-bit chunks. The MSB indicates whether there are more octets (1) or it is the last one (0). It means 0x00 to 0x7f encoded in 1 byte, 0x80 to 0x3fff encoded in 2 bytes, …


0x0f -> 0f
0x1000 -> 8020
0xffff -> ffff03
0xffffff -> ffffff07


Variable length byte (VarByte) is encoded as a variable length integer (VarInt) containing the length of the array followed by the bytes themselves: VarInt(len(bytes)) || bytes


Variable length string (VarString) is encoded as a variable length integer (VarInt) containing the length of the string followed by the bytes that represent the string itself:VarInt(len(str)) || str

Byte Order

All the internal number representation are in little-endian byte order.


Here is an example of a block header data that encoded using deterministic serialization:

CBOR Serialization

For non-deterministic data, such as networking messages, Pactus uses “Concise Binary Object Representation” or CBOR. CBOR is a binary data serialization format that is widely used in various application, including IoT, web services, security, and automotive, due to its compact representation and efficient parsing.

CBOR Me! is an online tool for encoding and decoding CBOR data, offering developers an easy way to test and validate their CBOR data without having to set up a local environment.


Here is an example of a vote message that encoded using CBOR.

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