B4X

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

See more ECC Examples

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.

B4X

Dim success As Boolean = False

'  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.

Dim sb As ChilkatStringBuilder
sb.Initialize
sb.Append("The quick brown fox jumps over the lazy dog")
Dim hash As String = sb.GetHash("sha256", "base64", "utf-8")

'  Load the ECDSA key to be used for signing.
Dim privKey As ChilkatPrivateKey
privKey.Initialize("privKey")
success = privKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem")
If success <> True Then
    Log(privKey.LastErrorText)
    Return
End If


Dim prng As ChilkatPrng
prng.Initialize
Dim ecdsa As ChilkatEcc
ecdsa.Initialize

'  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
ecdsa.AsnFormat = False

Dim ecdsaSigBase64 As String = ecdsa.SignHashENC(hash, "base64", privKey, prng)
If ecdsa.LastMethodSuccess <> True Then
    Log(ecdsa.LastErrorText)
    Return
End If


Log("ECDSA signature = " & ecdsaSigBase64)

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

Dim pubKey As ChilkatPublicKey
pubKey.Initialize
success = pubKey.LoadFromFile("qa_data/ecc/secp256r1-pubkey.pem")
If success <> True Then
    Log(pubKey.LastErrorText)
    Return
End If


'  Note: When verifying, Chilkat will auto-detect the format for both kinds of ECDSA signatures (ASN.1 or binary r+s)
Dim result As Int = ecdsa.VerifyHashENC(hash, ecdsaSigBase64, "base64", pubKey)
If result = 1 Then
    Log("Signature is valid.")
    Return
End If

If result = 0 Then
    Log("Signature is invalid.")
    Return
End If

If result < 0 Then
    Log(ecdsa.LastErrorText)
    Log("The VerifyHashENC method call failed.")
    Return
End If