@startuml
skinparam classFontSize 8
skinparam classFontName Helvetica
autonumber

participant "Application" as app
participant "PKCS #11" as pkcs

box "PKCS #11 - Signing And Verifying A Signature" #LightBlue
    participant app
    participant pkcs
end box

app -> pkcs: Acquire function list with C_GetFunctionList
pkcs -> app: Return CK_FUNCTION_LIST_PTR with supported functions

app -> pkcs: Initialize with C_Initialize

app -> pkcs: Query for a slot with C_GetSlotList
pkcs -> app: Return an array of CK_SLOT_IDs

app -> pkcs: Open a new session with a slot using C_OpenSession
pkcs -> app: Return a CK_SESSION_HANDLE

app -> pkcs: Log in to current session with C_Login

app -> pkcs: Initiate a find operation by passing a CK_ATTRIBUTEs template to C_FindObjectsInit
app -> pkcs: Request a CK_OBJECT_HANDLE
pkcs -> app: Return CK_OBJECT_HANDLE for the appropriate object
app -> pkcs: Clean up find operation with C_FindObjectsFinal

app -> pkcs: Start a digest operation using SHA-256 by passing CKM_SHA256 C_DigestInit
app -> pkcs: Provide bytes buffer of message to hash with C_DigestUpdate
app -> pkcs: Provide bytes buffer to store digest in with C_DigestFinal
pkcs -> app: Fill buffer with digest bytes

app -> pkcs: Start a sign operation by passing the signature mechanism and private key handle to C_SignInit
app -> pkcs: Provide bytes buffer of message hash and bytes buffer to store the signature to C_Sign
pkcs -> app: Fill signature buffer with signature bytes of hash buffer

app -> pkcs: Start a verify operation by passing the verify mechanism and public key handle to C_VerifyInit
app -> pkcs: Provide bytes buffer of message hash and bytes buffer of the signature to C_Verify
pkcs -> app: Return OK if public key could verify signature

app -> pkcs: Close session with C_CloseSession
app -> pkcs: Uninitialize with C_Finalize

@endumla