Add spec draft to README

README.md

@@ -23,3 +23,35 @@ npm run test-sc
 ./compile-circuits.sh
 ```
 
+
+## Spec draft
+
+### Deposit
+- user generates a random `secret` & `nullifier`
+- computes the `commitment`, which is the Poseidon hash: `commitment = H(coinCode, amount, secret, nullifier)`, where:
+	- `coinCode`: code that specifies which currency is being used (`0`==ETH)
+	- `amount`: the amount to be deposited
+	- `secret`: random, private
+	- `nullifier`: random
+- get all the commitments from the SmartContract
+- build the MerkleTree with the getted commitments
+- add the new computed `commitment` into the MerkleTree
+- generate zkSNARK proof, where is proving:
+	- prover knows the `secret` & `nullifier` for the `commitment`
+	- the transition from `RootOld` (the current one in the Smart Contract) to `RootNew` has been done following the rules (only one addition, no deletion)
+- user sends ETH to the smart contract `deposit` call, together with the zkProof data
+
+Deposit circuit can be found [here](https://github.com/miksi-labs/miksi-core/blob/master/circuits/deposit.circom).
+
+### Withdraw
+- user gets all the commitments from the SmartContract
+- build the MerkleTree with the getted commitments
+- generate the siblings for the `commitment` of which the user knows the `secret` & `nullifier`
+- generate zkSNARK proof, where is proving:
+        - user knows a `secret` for a public `nullifier`
+        - which `commitment` is in the MerkleTree
+        - which MerkleTree `root` is the one that knows the SmartContract
+- if the zkProof verification passes, and the nullifier was not already used, the Smart Contract sends the ETH to the specified address
+
+Withdraw circuit can be found [here](https://github.com/miksi-labs/miksi-core/blob/master/circuits/withdraw.circom).
+