Update erasue-coding.md

specs/erasue-coding.md

@@ -34,16 +34,15 @@ The Codex client performerasure coding locally before provding dataset to the ma
 Before data is provided to storage providers on the marketplace,
 clients must do the following:
 
-1.  Create data chunks from the data
-2.  Encode each chunk with Reed Solomon erasue coding, more explained below
+1.  Prepare dataset
+2.  Encode data with Reed Solomon erasue coding, more explained below
 3.  Derive an CID from encoded chunks share on the marketplace
 4.  Error correction by validator nodes once storage contract begins
 
- 
-### Create Data chunks
+### Preparing Data
 
 After the user has choosen the prefered data for storage through the marketplace,
-the Codex client will divide this data into chunks , e.g. 
+the Codex client will divide this data into chunks, e.g. $(c_1, c_2, c_3, \ldots, c_{n})$.
 Including the [manifest](manifest), the data chucks will be encoded based on the following parameters:
 
 ```js
@@ -56,7 +55,63 @@ struct encodingParms {
   strategy: 
 }
 ```
+### Encoding Data
+
+With Reed-Solomon algorithm, extra data chunks need to be created for the dataset.
+Parity blocks is added to the chucks of data before encoding.
+Once data is encoded, it is prepared to be transmitted.
+
+
+Below is the content of the dag-pb protobuf message 
+
+```protobuf
+   Message VerificationInfo {
+     bytes verifyRoot = 1;             # Decimal encoded field-element
+     repeated bytes slotRoots = 2;     # Decimal encoded field-elements
+   }
+   Message ErasureInfo {
+     optional uint32 ecK = 1;                            # number of encoded blocks
+     optional uint32 ecM = 2;                            # number of parity blocks
+     optional bytes originalTreeCid = 3;                 # cid of the original dataset
+     optional uint32 originalDatasetSize = 4;            # size of the original dataset
+     optional VerificationInformation verification = 5;  # verification information
+   }
+
+   Message Header {
+     optional bytes treeCid = 1;        # cid (root) of the tree
+     optional uint32 blockSize = 2;     # size of a single block
+     optional uint64 datasetSize = 3;   # size of the dataset
+     optional codec: MultiCodec = 4;    # Dataset codec
+     optional hcodec: MultiCodec = 5    # Multihash codec
+     optional version: CidVersion = 6;  # Cid version
+     optional ErasureInfo erasure = 7;  # erasure coding info
+   }
+```
+
+## Decode Data
+
+There are two node roles that will need to decode data.
+- Client nodes to read data
+- Validator nodes to verfiy storage providers are storing data as per the marketplace
+
+To ensure data is being stored by by storage providers, data will need to be decoded when vaildator nodes need download data slots.
 
 
 ## Security Considerations
 
+### Encoding Problem
+
+An adversarial storage provider can remove only the first element from more than half of the block, and the slot data can no longer be recovered from the data that the host stores.
+For example, with 1TB of slot data erasure coded into 256 data and parity shards, an adversary could strategically remove 129 bytes, and the data can no longer be fully recovered with the erasure coded data that is present on the host.
+
+### Recommended Solution
+
+we should perform our checks on entire shards to protect against adversarial erasure.
+In the Merkle storage proofs, we need to hash the entire shard, and then check that hash with a Merkle proof.
+Effectively the block size for Merkle proofs should equal the shard size of the erasure coding interleaving. Hashing large amounts of data will be expensive to perform in a SNARK, which is used to compress proofs in size in Codex.
+
+
+
+## Copyright
+
+## References