Block Header

Block Header

General format of a Block Header in a MimbleWimble/Grin:

Field	Description	Size
version	Version of the block	2 bytes
height	Height of this block since the genesis block (height 0)	8 bytes
timestamp	Timestamp at which the block was built	8 bytes
prev_hash	Hash of the block previous to this in the chain	32 bytes
prev_root	Root hash of the header MMR at the previous header	32 bytes
output_root	Merkle root of all the commitments in the TxHashSet	32 bytes
range_proof_root	Merkle root of all range proofs in the TxHashSet	32 bytes
kernel_root	Merkle root of all transaction kernels in the TxHashSet	32 bytes
total_kernel_offset	Total accumulated sum of kernel offsets since genesis block.	32 bytes
output_mmr_size	Total size of the output MMR after applying this block.	8 bytes
kernel_mmr_size	Total size of the kernel MMR after applying this block.	8 bytes
		Sub-Total: 226 bytes
-	-	-
pow	Proof of work data	For cuck(AR)oo 29: 174 bytes. For cuck(AT)oo 31: 184 bytes.
		Total: 400 bytes for C29 or 410 bytes for C31

PoW

General format of a Proof Of Work in a MimbleWimble/Grin:

Field	Description	Size
total_difficulty	Total accumulated difficulty since genesis block	8 bytes
secondary_scaling	Variable difficulty scaling factor for secondary proof of work	4 bytes
nonce	Nonce increment used to mine this block.	8 bytes
proof	Proof of work data	cuckoo_size: 1byte cuckoo_solution of C29: 42∗29 bits=153 bytes cuckoo_solution of C31: 42∗31 bits=163 bytes
		Sub-Total: 174 bytes for C29 and 184 bytes for C31

Example

Here is a principle example of a MimbleWimle/Grin block header. The related block is included in Mainnet chain block: 1869.

Offset	Field	Hex Value
0	version	0001
2	height	000000000000074d
10	timestamp	000000005c3ff107
18	prev_hash	00001915c97bfad5bf9bb30a1035771446770502a937bd16a8c8a8f1fc6db730
50	prev_root	2eb356e36c03f16796dd4a6eef8cbcbeabaade84eecf013516367b376d646db7
82	output_root	b56ccc990181d04d57585d3f0163b4f636fe3208a024596d14221bfa7739e693
114	range_proof_root	a341b87862f430f9dda5fd0b88be175b6cc81b5e84bf6882d98cc31750b5001a
146	kernel_root	b3e9708378ef256d479c6b166ba0a56c26d1b2e985c5e48065dbaa8a1fa6e606
178	total_kernel_offset	0755f37fa67bc3d3f0a7eddec7117013be42afff3602e7480d7271fff92763f1
210	output_mmr_size	0000000000001445
218	kernel_mmr_size	0000000000001130
226	total_difficulty	00000108e24af3bb
234	secondary_scaling	00000473
238	nonce	712493895227b883
246	edge_bits	1d
247	edge_nonces	43c8d2e098ba28f4f3748aab7d8be1aab3353259e6c6d4c046293f1c2f92afe7c5868bc5007fc51bae789ab3776d7efefb71547144b70ae8e764921bad8cb821a0c5d2adb455e1c406e1b2e39a2db51d7c552e4c1dd78bde1eea91f0843da6b3f1cb86e4ccb93371452b66c0ab292cd42525bcbf832fe358a3b22bcf7615e8397516ad8135a709213a77347cf4de104df5585984df0246fa03
400

Description

To reproduce the proof of work for block 1968 with the reference cpu mean solver available as a grin-miner plugin, compile with HEADERLEN=246 and run

$ ./mean29x8 -x 0001000000000000074d000000005c3ff10700001915c97bfad5bf9bb30a1035771446770502a937bd16a8c8a8f1fc6db7302eb356e36c03f16796dd4a6eef8cbcbeabaade84eecf013516367b376d646db7b56ccc990181d04d57585d3f0163b4f636fe3208a024596d14221bfa7739e693a341b87862f430f9dda5fd0b88be175b6cc81b5e84bf6882d98cc31750b5001ab3e9708378ef256d479c6b166ba0a56c26d1b2e985c5e48065dbaa8a1fa6e6060755f37fa67bc3d3f0a7eddec7117013be42afff3602e7480d7271fff92763f10000000000001445000000000000113000000108e24af3bb00000473712493895227b883 -n 659720595 -s
Looking for 42-cycle on cuckaroo29("",659720595) with 50% edges
Using 3752MB bucket memory at 106e55000,
1x25MB thread memory at 1f1695000,
8-way siphash, and 128 buckets.
nonce 659720595 k0 k1 k2 k3 2a19d2a799213637 34da44e4123eb76 aaf4eb8132d503a 25af7154b3a0c87c
genUVnodes size 536870912 rdtsc: 11582318731
sortVnodes round  1 size 339366261 rdtsc: 12444604916
trimedges id 0 round  3 size 94071091 rdtsc: 4322291767
trimedges id 0 round  7 size 26425030 rdtsc: 864460691
trimrename id 0 round 14 size 8139955 rdtsc: 425070799 maxnnid 31733
trimrename id 0 round 15 size 7201653 rdtsc: 444656879 maxnnid 27950
trimedges1 id 0 round 31 size 1906932 rdtsc: 35389089
trimedges1 id 0 round 63 size 497051 rdtsc: 22820057
trimrename1 id 0 round 66 size 454675 rdtsc: 26397569 maxnnid 1942
trimrename1 id 0 round 67 size 441696 rdtsc: 23213276 maxnnid 1854
  6-cycle found
  8-cycle found
  2-cycle found
  32-cycle found
  42-cycle found
matchUnodes id 0 rdtsc: 9459309257
findcycles rdtsc: 10050627872
Time: 18049 ms
Solution d2c843 145d4c7 29d3cfd 316fb57 35b3aae 3732c99 51b0353 5e387e5 5e7af92 62c5c36 6f15fc0 734f15c 7e6d77b a38fdff add11c5 c9cfd01 cad1b92 d010dc4 d2b74b1 d89c2ab e3b2e10 eda96cd 10b955f0 117ae3a9 11ea1ede 11ec2784 12fc6ce9 1399c90d 1457133b 15e03315 1750b0a6 17f784a4 18e32f83 195d951a 1a055db3 1a2cea73 1a73581a 1b9d1084 1bd1f0d1 1ea9a21b 1f845958 1fd23016
Verified with cyclehash 9c50298a86c18d6660a65f94759354b4ca27122d2486cad224bbb86f347a35fb
1 total solutions

Note that this solver overwrites the last aligned 4 bytes of the header with the provided nonce, so we pass the decimal equivalent of 0x27528993. Finally, note that this solver computes cyclehashes on the uncompressed edge nonces whereas Grin computes it on the 153 bytes (with 0 bit padding) compressed edge nonces.