@startuml grin-transaction title **Current Grin Tranaction Workflow** Accurate as of Feb 12th, 2018 - Master branch only end title actor "Sender" as sender actor "Recipient" as recipient entity "Grin Node" as grin_node == Phase 1 - Sender Initiation == note left of sender 1: Create Transaction **UUID** (for reference and maintaining correct state) 2: Set **lock_height** for output (current chain height) 3: Select **inputs** using desired selection strategy 4: Create **change_output** 5: Select blinding factor for **change_output** end note sender -> sender: Lock **inputs** in wallet sender -> sender: Store **change_output** in wallet with status "Unconfirmed" note left of sender 6: Calculate **tx_weight**: MAX(-1 * **num_inputs** + 4 * **num_change_outputs** + 1, 1) (+1 covers a single output on the receiver's side) 7: Calculate **fee**: **tx_weight** * 1_000_000 nG 8: Calculate total blinding excess sum for all inputs and outputs **xS** (private scalar) 9: Select a random nonce **kS** (private scalar) 10: Multiply **xS** and **kS** by generator G to create public curve points **xSG** and **kSG** end note sender -> recipient: **UUID**, **inputs**, **change_output**, **fee**, **lock_height**, **kSG**, **xSG** == Phase 2 - Receiver Initiation == note right of recipient 1: Check fee against number of **inputs**, **change_outputs** +1 * **receiver_output**) 2: Create **receiver_output** 3: Choose random blinding factor for **receiver_output** **xR** (private scalar) end note recipient -> recipient: Store **receiver_output** in wallet with status "Unconfirmed" note right of recipient 4: Calculate message **M** = **fee | lock_height ** 5: Choose random nonce **kR** (private scalar) 6: Multiply **xR** and **kR** by generator G to create public curve points **xRG** and **kRG** 7: Compute Schnorr challenge **e** = Blake2(**M** | **kRG** + **kSG**) 8: Compute Recipient Schnorr signature **sR** = **kR** + **e** * **xR** end note alt All Okay recipient --> sender: Okay - **UUID**, **sR**, **xRG**, **kRG** else Any Failure recipient -> recipient: Remove **receiver_output** from wallet recipient ->x]: Abort recipient --> sender: Error sender -> sender: Roll back **inputs** and **change_output** [x<- sender: Abort end == Phase 3 - Sender Confirmation == note left of sender 1: Calculate message **M** = **fee | lock_height ** 2: Compute Schnorr challenge **e** = Blake2(**M** | **kRG** + **kSG**) 3: Verify **sR** by verifying **kRG** + **e** * **xRG** = **sRG** 4: Compute Sender Schnorr signature **sS** = **kS** + **e** * **xS** end note sender -> recipient: **UUID**, **sS** == Phase 4 - Receiver Confirmation == note right of recipient 1: Verify **sS** by verifying **kSG** + **e** * **xSG** = **sSG** 2: Calculate final signature **s** = (**sS**+**sR**, **kSG**+**kRG**) 3: Calculate public key for **s**: **xG** = **xRG** + **xSG** 3: Verify **s** against excess values in final transaction using **xG** 4: Create Transaction Kernel Containing: Signature **s** Public key **xG** **fee** **lock_height** end note recipient -> recipient: Create final transaction **tx** recipient -> grin_node: Post **tx** to mempool grin_node --> recipient: "Ok" alt All Okay recipient --> sender: "Ok" - **UUID** ...Await confirmation... recipient -> grin_node: Confirm **receiver_output** recipient -> recipient: Change status of **reciever_output** to "Confirmed" sender -> grin_node: Confirm **change_output** sender -> sender: Change status of **inputs** to "Spent" sender -> sender: Change status of **change_output** to "Confirmed" else Any Error recipient -> recipient: Remove **receiver_output** from wallet recipient ->x]: Abort recipient --> sender: Error sender -> sender: Roll back **inputs** and **change_output** [x<- sender: Abort end @enduml