Reserved Space

Everything you need to know about the Reserved Space

Why a Reserved Space

In RandomX system there is not a unique Blob that all miners work on. In fact in RandomX each miner must get a different blob, two different miners do not mine with the same blob. The Reserved Space is a specific location of the blob that is supposed to be updated to generate unique blobs for each miner.

How it works

Monero: In Monero, there is a specific location in the block templates where it is possible to set extraNonce data that will then generate different blob hashes when the block template is hashed to generate the blob.

Etica: Etica doesn't use a block template system so the Reserved Space works slightly differently than Monero. Etica uses a ReservedSpaceOffset at position 55bytes, ReservedSpaceSize is 8bytes, so ReservedSpace data will be inserted in the blob at position 55-62bytes. Here is how Etica Reserved Space works: 1. extraNonce: Each miner get an extraNonce (random 8bytes string). 2. Update the blob a) Then a 32bytes hash is generated using keccack256 (also named soliditysha3 ) to hash (address, extraNonce, challengeNumber) like this:

extraNonceHash = web3utils.soliditySha3(poolAddress, extraNonce, challengeNumber);

The address input must be the address that sends the transaction on blockchain. extraNonce input is the random 8bytes string generated specifically for a miner. challengeNumber input must be the current ETI challengeNumber.

b) Then the extraNonceHash 32bytes is truncated to only take the first 8bytes. This 8bytes data will then be placed at ReservedSpaceOffset position (at position 55-62bytes) Example of the whole process to generate a specific blob for each miner:

Example We'll be using the following randomxBlob example (randomxBlob is a general blob retireved from blockchain that is updated for each new block): da4670bae10db93a46fad64b14d091189cafa19f61674963f2f2d635b4f2a812685f828da7adb7de554b4090363931bde43a6042eafd6197fbf4866191c9e845ae615393f941f4bb9f92b7ed537c2fb7 For reminder: NonceOffset is at position 39-42bytes, this is where the miners will iterate to put random 4bytes nonces (will be put at the position of fa19f61674) But for our example we need to pay attention to the ReservedSpaceOffset:

da4670bae10db93a46fad64b14d091189cafa19f61674963f2f2d635b4f2a812685f828da7adb7de554b4090363931bde43a6042eafd6197fbf4866191c9e845ae615393f941f4bb9f92b7ed537c2fb7 ReservedSpaceOffset is at position 55-62bytes, this is where each miner must put a unique random 8bytes data to make sure they are the only one mining with this specific blob. In our example each miner would get a unique blob by replacing the data at the position of 685f828da7adb7de ReservedSpace blob examples:

Example1: Miner1 gets extraNonce: 98b88b8366a79836 (random 8bytes) By applying the process explain above (2. Update the blob) the Miner1 would generate a random ReservedHash 8bytes data from the 8bytes extraNonce. Then this ReservedHash will be placed in the blob at position 55-62bytes. For instance in our example let's say the extraNonce 98b88b8366a79836 generates this ReservedHash: bc52365203f86653. The randomxBlob for Miner1 would then be updated like this: da4670bae10db93a46fad64b14d091189ca89abcdef963f2f2d635b4f2a812bc52365203f86653554b4090363931bde43a6042eafd6197fbf4866191c9e845ae615393f941f4bb9f92b7ed537c2fb7 This updated blob is the blob to send to Miner1 only

Example2: Miner2 would get another extraNonce, thus would get another 8bytes ReservedHash. The blob for Miner2 would also be updated with the personalised ReservedHash of Miner2 exactly like for Miner1. Miner2 gets extraNonce: 3fae5b7c9d2a4f8b (random 8bytes) This leads to ReservedHash: 7d2e8f1a6c4b9035 The randomxBlob for Miner2 would then be updated like this: da4670bae10db93a46fad64b14d091189ca5f6e7d8c963f2f2d635b4f2a8127d2e8f1a6c4b9035554b4090363931bde43a6042eafd6197fbf4866191c9e845ae615393f941f4bb9f92b7ed537c2fb7

Note: When passing the Nonce to Ethereum related functions like Ethereum libraries it is often necessary to add 0x at the begining of the Nonce. For instance here it would beb 0x89abcdef and 0x5f6e7d8c.