add a readme file

README.md

@@ -0,0 +1,64 @@
+# SSV Distributed Key Generation Spec
+
+## Introduction
+This repository contains spec of distributed key generation (DKG) used in SSV. Based on verifiable secret sharing, DKG allows a set of *n* operators to generate a  **BLS** key share for each operator, such that a BLS private key can only be used when threshold *t* out of *n* operators agree. 
+
+---
+
+## Functionalities
+Operations are initiated by an initiator, and executed by operators. An initiator can initiate:
+
+### Init
+When a init message is sent to the operators, all operators participate and run a DKG ceremony to create key shares. Each operator generates a result with a **proof** (see below) to show the correctness of execution. Proofs are referred to when an initiator asks for re-sign or reshare. 
+
+### Re-sign
+In the case where the nonces of a DKG ceremony is not correct, to prevent replay attack, the initiator sends re-sign messages for operators to create new signatures with correct nonces without generating new key shares. 
+
+### Reshare
+When the set of operators changed (including change of size and change of operators), a reshare is initiated to generate new key shares among the new operators. This process requires participation from *t* old operators and all new operators. 
+
+---
+
+## Result and Proof struct
+After execution of init, re-sign and reshare, a **result** is returned by the operators for validation and verification.
+```go
+type Result struct {
+	// Operator ID
+	OperatorID uint64
+	// RequestID for the DKG instance (not used for signing)
+	RequestID [24]byte `ssz-size:"24"`
+	// Partial Operator Signature of Deposit data
+	DepositPartialSignature []byte `ssz-size:"96"`
+	// SSV owner + nonce signature
+	OwnerNoncePartialSignature []byte `ssz-size:"96"`
+	// Signed proof for the ceremony
+	SignedProof SignedProof
+}
+```
+
+In a **result**, the **SignedProof** is a **Proof** with a signature. A **Proof** contains:
+```go
+type Proof struct {
+	// the resulting public key corresponding to the shared private key
+	ValidatorPubKey []byte `ssz-size:"48"`
+	// standard SSV encrypted share
+	EncryptedShare []byte `ssz-max:"512"`
+	// the share's BLS pubkey
+	SharePubKey []byte `ssz-size:"48"`
+	// owner address
+	Owner [20]byte `ssz-size:"20"`
+}
+```
+*ValidatorPubKey*, *EncryptedShare*, and *Owner* are to identify information of the validator and the operator in SSV netwwork, the *SharePubKey* is computed by the operator after the DKG ceremony using the obtained secret share as the private key.
+
+---
+
+## Testing
+The tests are located in the `testing/` folder. To run tests, use:
+```shell
+go generate ./...
+```
+then:
+```shell
+go test testing
+```