(PureBasic) Create ECSDA Signature using Raw r and s Format (not ASN.1)

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Demonstrates how to create an ECDSA signature using the raw r/s format.

ECDSA signatures have two equal sized parts, r and s. There are two common formats for encoding the signature:

(a) Concatenating the raw byte array of r and s
(b) Encoding both into a structured ASN.1 / DER sequence.

This example demonstrates how to create a signature that is a byte array of r and s concatenated.

Note: This example requires Chilkat v9.5.0.97 or greater.

Chilkat PureBasic Module Download Chilkat PureBasic Module

IncludeFile "CkStringBuilder.pb"
IncludeFile "CkPrivateKey.pb"
IncludeFile "CkPrng.pb"
IncludeFile "CkPublicKey.pb"
IncludeFile "CkEcc.pb"

Procedure ChilkatExample()

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

    ; To create an ECDSA signature, the data first needs to be hashed.  Then the hash
    ; is signed.

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

    CkStringBuilder::ckAppend(sb,"The quick brown fox jumps over the lazy dog")
    hash.s = CkStringBuilder::ckGetHash(sb,"sha256","base64","utf-8")

    ; Load the ECDSA key to be used for signing.
    privKey.i = CkPrivateKey::ckCreate()
    If privKey.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success.i = CkPrivateKey::ckLoadPemFile(privKey,"qa_data/ecc/secp256r1-key-pkcs8.pem")
    If success <> 1
        Debug CkPrivateKey::ckLastErrorText(privKey)
        CkStringBuilder::ckDispose(sb)
        CkPrivateKey::ckDispose(privKey)
        ProcedureReturn
    EndIf

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

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

    ; Produce a signature that is not ASN.1, but is instead the concatenation
    ; of the raw r and s signature parts.
    ; This feature was added in Chilkat v9.5.0.97
    CkEcc::setCkAsnFormat(ecdsa, 0)

    ecdsaSigBase64.s = CkEcc::ckSignHashENC(ecdsa,hash,"base64",privKey,prng)
    If CkEcc::ckLastMethodSuccess(ecdsa) <> 1
        Debug CkEcc::ckLastErrorText(ecdsa)
        CkStringBuilder::ckDispose(sb)
        CkPrivateKey::ckDispose(privKey)
        CkPrng::ckDispose(prng)
        CkEcc::ckDispose(ecdsa)
        ProcedureReturn
    EndIf

    Debug "ECDSA signature = " + ecdsaSigBase64

    ; -----------------------------------------------------------
    ; Now let's verify the signature using the public key.

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

    success = CkPublicKey::ckLoadFromFile(pubKey,"qa_data/ecc/secp256r1-pubkey.pem")
    If success <> 1
        Debug CkPublicKey::ckLastErrorText(pubKey)
        CkStringBuilder::ckDispose(sb)
        CkPrivateKey::ckDispose(privKey)
        CkPrng::ckDispose(prng)
        CkEcc::ckDispose(ecdsa)
        CkPublicKey::ckDispose(pubKey)
        ProcedureReturn
    EndIf

    ; Note: When verifying, Chilkat will auto-detect the format for both kinds of ECDSA signatures (ASN.1 or binary r+s)
    result.i = CkEcc::ckVerifyHashENC(ecdsa,hash,ecdsaSigBase64,"base64",pubKey)
    If result = 1
        Debug "Signature is valid."
        CkStringBuilder::ckDispose(sb)
        CkPrivateKey::ckDispose(privKey)
        CkPrng::ckDispose(prng)
        CkEcc::ckDispose(ecdsa)
        CkPublicKey::ckDispose(pubKey)
        ProcedureReturn
    EndIf

    If result = 0
        Debug "Signature is invalid."
        CkStringBuilder::ckDispose(sb)
        CkPrivateKey::ckDispose(privKey)
        CkPrng::ckDispose(prng)
        CkEcc::ckDispose(ecdsa)
        CkPublicKey::ckDispose(pubKey)
        ProcedureReturn
    EndIf

    If result < 0
        Debug CkEcc::ckLastErrorText(ecdsa)
        Debug "The VerifyHashENC method call failed."
        CkStringBuilder::ckDispose(sb)
        CkPrivateKey::ckDispose(privKey)
        CkPrng::ckDispose(prng)
        CkEcc::ckDispose(ecdsa)
        CkPublicKey::ckDispose(pubKey)
        ProcedureReturn
    EndIf



    CkStringBuilder::ckDispose(sb)
    CkPrivateKey::ckDispose(privKey)
    CkPrng::ckDispose(prng)
    CkEcc::ckDispose(ecdsa)
    CkPublicKey::ckDispose(pubKey)


    ProcedureReturn
EndProcedure