Lianja

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.

Lianja

llSuccess = .F.

// 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.

loSb = createobject("CkStringBuilder")
loSb.Append("The quick brown fox jumps over the lazy dog")
lcHash = loSb.GetHash("sha256","base64","utf-8")

// Load the ECDSA key to be used for signing.
loPrivKey = createobject("CkPrivateKey")
llSuccess = loPrivKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem")
if (llSuccess <> .T.) then
    ? loPrivKey.LastErrorText
    release loSb
    release loPrivKey
    return
endif

loPrng = createobject("CkPrng")
loEcdsa = createobject("CkEcc")

// 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
loEcdsa.AsnFormat = .F.

lcEcdsaSigBase64 = loEcdsa.SignHashENC(lcHash,"base64",loPrivKey,loPrng)
if (loEcdsa.LastMethodSuccess <> .T.) then
    ? loEcdsa.LastErrorText
    release loSb
    release loPrivKey
    release loPrng
    release loEcdsa
    return
endif

? "ECDSA signature = " + lcEcdsaSigBase64

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

loPubKey = createobject("CkPublicKey")
llSuccess = loPubKey.LoadFromFile("qa_data/ecc/secp256r1-pubkey.pem")
if (llSuccess <> .T.) then
    ? loPubKey.LastErrorText
    release loSb
    release loPrivKey
    release loPrng
    release loEcdsa
    release loPubKey
    return
endif

// Note: When verifying, Chilkat will auto-detect the format for both kinds of ECDSA signatures (ASN.1 or binary r+s)
lnResult = loEcdsa.VerifyHashENC(lcHash,lcEcdsaSigBase64,"base64",loPubKey)
if (lnResult = 1) then
    ? "Signature is valid."
    release loSb
    release loPrivKey
    release loPrng
    release loEcdsa
    release loPubKey
    return
endif

if (lnResult = 0) then
    ? "Signature is invalid."
    release loSb
    release loPrivKey
    release loPrng
    release loEcdsa
    release loPubKey
    return
endif

if (lnResult < 0) then
    ? loEcdsa.LastErrorText
    ? "The VerifyHashENC method call failed."
    release loSb
    release loPrivKey
    release loPrng
    release loEcdsa
    release loPubKey
    return
endif



release loSb
release loPrivKey
release loPrng
release loEcdsa
release loPubKey