Block Header Binary Encoding

BlockHeader Binary Format For Chain Graphs of Degree Three without Hash

defined in Chainweb.BlockHeader

Size	Bytes	Value
8	0-7	flags
8	8-15	time
32	16-47	parent
110	48-157	adjacents
32	158-189	target
32	190-221	payload
4	222-225	chain
32	226-257	weight
8	258-265	height
4	266-269	version
8	270-277	epoch start
8	278-285	nonce
32	286-317	hash

total: 318 bytes

Adjacent Parents Record (length 3):

Bytes	Value
0-1	length
2-109	adjacents

total: 110 bytes

Adjacent Parent:

Bytes	Value
0-3	chain
4-35	hash

total: 36 bytes

Fields

POW related values:

Arithmetic operations and comparisons on parent, target, weight, and hash interpret the value as unsigned 256 bit integral numbers in little endian encoding.

Time Stamps:

time and epoch start are a little endian twoth complement encoded integral numbers that counts SI microseconds since POSIX epoch. These numbers are always positive (highest bit is 0).

Numbers:

• height is a little endian encoded unsigned integral 64 bit number.
• length is a little endian encoded unsigned integral 16 bit number.

Version:

version identifies the chainweb version. It is a 32 bit value in little endian encoding. Values up to 0x0000FFFF are reserved for production versions (which includes Development and testnets).

value	version
0x00000001	Development
0x00000004	Testnet02

Other:

• nonce is any sequence of 8 bytes that is only compared for equality.
• chain is any sequence of 4 bytes that identifies a chain and can be compared for equality.
• payload is any sequence of 32 bytes that is a cryptographic hash of the payload associated with the block and can be compared for equality.
• flags are eight bytes of value 0x0 that are reserved for future use.

Work Header Binary Format

The work bytes received the /miner/work endpoint is slightly different than the above header format. These headers do not include the block hash, instead prefixing the header above (without hash) with chain id and hash target bytes.

The first 36 bytes are informational. Only the bytes from position 36 to the end are subject the the POW hash computation.

The final 8 bytes are the nonce. The creation time is encoded in bytes 44-52 (see above for details of the encoding). Miners are encouraged to update the time to reflect the solve time for the block as close as possible. A larger value for the creation time increases the accuracy of difficulty adjustment which is in the interest of miners -- the high difficulty guarantees that the outcome of the race of winning blocks is determined by actual hash power. However, blocks that are predated (i.e. have a a creation time that is in the future) are rejected during block header validation.

Miners must not change or make any assumptions about the content of the "reserved" bytes.

Defined in Chainweb.Miner.Core

Size	Bytes	Value
4	0-3	chain
32	4-35	hash-target
8	36-43	reserved
8	44-51	time
298	52-313	reserved
8	314-321	nonce

total: 322 bytes