(PowerShell) 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 .NET Downloads Chilkat .NET Assemblies

Add-Type -Path "C:\chilkat\ChilkatDotNet47-9.5.0-x64\ChilkatDotNet47.dll"

# 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 = New-Object Chilkat.StringBuilder
$sb.Append("The quick brown fox jumps over the lazy dog")
$hash = $sb.GetHash("sha256","base64","utf-8")

# Load the ECDSA key to be used for signing.
$privKey = New-Object Chilkat.PrivateKey
$success = $privKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem")
if ($success -ne $true) {
    $($privKey.LastErrorText)
    exit
}

$prng = New-Object Chilkat.Prng
$ecdsa = New-Object Chilkat.Ecc

# 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

$ecdsaSigBase64 = $ecdsa.SignHashENC($hash,"base64",$privKey,$prng)
if ($ecdsa.LastMethodSuccess -ne $true) {
    $($ecdsa.LastErrorText)
    exit
}

$("ECDSA signature = " + $ecdsaSigBase64)

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

$pubKey = New-Object Chilkat.PublicKey
$success = $pubKey.LoadFromFile("qa_data/ecc/secp256r1-pubkey.pem")
if ($success -ne $true) {
    $($pubKey.LastErrorText)
    exit
}

# Note: When verifying, Chilkat will auto-detect the format for both kinds of ECDSA signatures (ASN.1 or binary r+s)
$result = $ecdsa.VerifyHashENC($hash,$ecdsaSigBase64,"base64",$pubKey)
if ($result -eq 1) {
    $("Signature is valid.")
    exit
}

if ($result -eq 0) {
    $("Signature is invalid.")
    exit
}

if ($result -lt 0) {
    $($ecdsa.LastErrorText)
    $("The VerifyHashENC method call failed.")
    exit
}