(PureBasic) Create a JWS Using ECDSA P-256 SHA-256

Creates and validates a JSON Web Signature (JWS) that uses ECDSA P-256 SHA-256

Note: This example requires Chilkat v9.5.0.66 or greater.

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IncludeFile "CkJws.pb"
IncludeFile "CkStringBuilder.pb"
IncludeFile "CkPrivateKey.pb"
IncludeFile "CkJsonObject.pb"
IncludeFile "CkPublicKey.pb"

Procedure ChilkatExample()

    ; This requires the Chilkat API to have been previously unlocked.
    ; See Global Unlock Sample for sample code.

    ; Note: This example requires Chilkat v9.5.0.66 or greater.

    ; Use the following ECC key loaded from JWK format.
    sbJwk.i = CkStringBuilder::ckCreate()
    If sbJwk.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkStringBuilder::ckAppend(sbJwk,"{" + Chr(34) + "kty" + Chr(34) + ":" + Chr(34) + "EC" + Chr(34) + ",")
    CkStringBuilder::ckAppend(sbJwk,Chr(34) + "crv" + Chr(34) + ":" + Chr(34) + "P-256" + Chr(34) + ",")
    CkStringBuilder::ckAppend(sbJwk,Chr(34) + "x" + Chr(34) + ":" + Chr(34) + "f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU" + Chr(34) + ",")
    CkStringBuilder::ckAppend(sbJwk,Chr(34) + "y" + Chr(34) + ":" + Chr(34) + "x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0" + Chr(34) + ",")
    CkStringBuilder::ckAppend(sbJwk,Chr(34) + "d" + Chr(34) + ":" + Chr(34) + "jpsQnnGQmL-YBIffH1136cspYG6-0iY7X1fCE9-E9LI" + Chr(34))
    CkStringBuilder::ckAppend(sbJwk,"}")

    eccKey.i = CkPrivateKey::ckCreate()
    If eccKey.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; Note: This example loads the ECDSA key from JWK format.  Any format can be loaded
    ; into the private key object. (See the online reference documentation..)
    success.i = CkPrivateKey::ckLoadJwk(eccKey,CkStringBuilder::ckGetAsString(sbJwk))
    If success <> 1
        Debug CkPrivateKey::ckLastErrorText(eccKey)
        CkStringBuilder::ckDispose(sbJwk)
        CkPrivateKey::ckDispose(eccKey)
        ProcedureReturn
    EndIf

    ; Create the JWS Protected Header
    jwsProtHdr.i = CkJsonObject::ckCreate()
    If jwsProtHdr.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkJsonObject::ckAppendString(jwsProtHdr,"alg","ES256")

    jws.i = CkJws::ckCreate()
    If jws.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; Set the protected header:
    signatureIndex.i = 0
    CkJws::ckSetProtectedHeader(jws,signatureIndex,jwsProtHdr)

    ; Set the ECC key:
    CkJws::ckSetPrivateKey(jws,signatureIndex,eccKey)

    ; Set the payload.
    bIncludeBom.i = 0
    payloadStr.s = "In our village, folks say God crumbles up the old moon into stars."
    CkJws::ckSetPayload(jws,payloadStr,"utf-8",bIncludeBom)

    ; Create the JWS
    ; By default, the compact serialization is used.
    jwsCompact.s = CkJws::ckCreateJws(jws)
    If CkJws::ckLastMethodSuccess(jws) <> 1
        Debug CkJws::ckLastErrorText(jws)
        CkStringBuilder::ckDispose(sbJwk)
        CkPrivateKey::ckDispose(eccKey)
        CkJsonObject::ckDispose(jwsProtHdr)
        CkJws::ckDispose(jws)
        ProcedureReturn
    EndIf

    Debug "JWS: " + jwsCompact

    ; Note: ECC signatures use random values, so the output will be different each time a signature is produced.
    ; sample output:
    ; JWS: eyJhbGciOiJFUzI1NiJ9.SW4gb3VyIHZpbGxhZ2UsIGZvbGtzIHNheSBHb2QgY3J1bWJsZXMgdXAgdGhlIG9sZCBtb29uIGludG8gc3RhcnMu.J6EGTNkeuEjehHHBu0SOKzifm8r35wbx49A5964pxzB7gannyZZPMkK7vmlaPJ-K8Xmm8cZsQySAPC12Xd8avw

    ; Now load the JWS, validate, and recover the original text.
    jws2.i = CkJws::ckCreate()
    If jws2.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; Load the JWS.
    success = CkJws::ckLoadJws(jws2,jwsCompact)

    eccPubKey.i = CkPrivateKey::ckGetPublicKey(eccKey)

    ; Set the ECC public key used for validation.
    signatureIndex = 0
    CkJws::ckSetPublicKey(jws2,signatureIndex,eccPubKey)
    CkPublicKey::ckDispose(eccPubKey)

    ; Validate the 1st (and only) signature at index 0..
    v.i = CkJws::ckValidate(jws2,signatureIndex)
    If v < 0
        ; Perhaps Chilkat was not unlocked or the trial expired..
        Debug "Method call failed for some other reason."
        Debug CkJws::ckLastErrorText(jws2)
        CkStringBuilder::ckDispose(sbJwk)
        CkPrivateKey::ckDispose(eccKey)
        CkJsonObject::ckDispose(jwsProtHdr)
        CkJws::ckDispose(jws)
        CkJws::ckDispose(jws2)
        ProcedureReturn
    EndIf

    If v = 0
        Debug "Invalid signature.  The ECC key was incorrect, the JWS was invalid, or both."
        CkStringBuilder::ckDispose(sbJwk)
        CkPrivateKey::ckDispose(eccKey)
        CkJsonObject::ckDispose(jwsProtHdr)
        CkJws::ckDispose(jws)
        CkJws::ckDispose(jws2)
        ProcedureReturn
    EndIf

    ; If we get here, the signature was validated..
    Debug "Signature validated."

    ; Recover the original content:
    Debug CkJws::ckGetPayload(jws2,"utf-8")

    ; Examine the protected header:
    joseHeader.i = CkJws::ckGetProtectedHeader(jws2,signatureIndex)
    If CkJws::ckLastMethodSuccess(jws2) <> 1
        Debug "No protected header found at the given index."
        CkStringBuilder::ckDispose(sbJwk)
        CkPrivateKey::ckDispose(eccKey)
        CkJsonObject::ckDispose(jwsProtHdr)
        CkJws::ckDispose(jws)
        CkJws::ckDispose(jws2)
        ProcedureReturn
    EndIf

    CkJsonObject::setCkEmitCompact(joseHeader, 0)

    Debug "Protected (JOSE) header:"
    Debug CkJsonObject::ckEmit(joseHeader)
    CkJsonObject::ckDispose(joseHeader)

    ; Output:

    ; Signature validated.
    ; In our village, folks say God crumbles up the old moon into stars.
    ; Protected (JOSE) header:
    ; { 
    ;   "alg": "ES256"
    ; }


    CkStringBuilder::ckDispose(sbJwk)
    CkPrivateKey::ckDispose(eccKey)
    CkJsonObject::ckDispose(jwsProtHdr)
    CkJws::ckDispose(jws)
    CkJws::ckDispose(jws2)


    ProcedureReturn
EndProcedure