(PowerShell) DSA R,S Signature Values

See more DSA Examples

Creates a DSA signature. Gets r,s values from the signature. Re-creates the DSA signature ASN.1 from the r,s values. Then verifies the signature using the re-created ASN.1 DSA signature.

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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.

$crypt = New-Object Chilkat.Crypt2

$crypt.EncodingMode = "hex"
$crypt.HashAlgorithm = "sha-1"

$hashStr = $crypt.HashFileENC("qa_data/hamlet.xml")
$("hash to sign: " + $hashStr)

$dsa = New-Object Chilkat.Dsa

$pemPrivateKey = $dsa.LoadText("qa_data/dsa/dsaPrivKey2.pem")
$success = $dsa.FromPem($pemPrivateKey)
if ($success -eq $false) {
    $($dsa.LastErrorText)
    exit
}

# Load the hash to be signed into the DSA object:
$success = $dsa.SetEncodedHash("hex",$hashStr)
if ($success -eq $false) {
    $($dsa.LastErrorText)
    exit
}

# Sign the hash.
$success = $dsa.SignHash()
if ($success -eq $false) {
    $($dsa.LastErrorText)
    exit
}

# Get the ASN.1 signature.
$asnSig = $dsa.GetEncodedSignature("base64")
$("Signature: " + $asnSig)

# Examine the details of the ASN.1 signature.
# We want to get the r,s values as hex strings..
$asn = New-Object Chilkat.Asn
$success = $asn.LoadEncoded($asnSig,"base64")
if ($success -eq $false) {
    $($asn.LastErrorText)
    exit
}

# Get the ASN.1 as XML.
$xml = New-Object Chilkat.Xml
$success = $xml.LoadXml($asn.AsnToXml())
$("Signature as XML: ")
$($xml.GetXml())

# Sample XML shown here.
# The r and s values are the two hex strings in the XML.

# <?xml version="1.0" encoding="utf-8"?>
# <sequence>
#     <int>2C187F3AB6E47A66497B86CE97BB39E2133810F5</int>
#     <int>588E53D3F7B69636B48FD7175E99A3961BD7D775</int>
# </sequence>

# Pretend we're starting with r,s
$r = "2C187F3AB6E47A66497B86CE97BB39E2133810F5"
$s = "588E53D3F7B69636B48FD7175E99A3961BD7D775"

# Build the XML that will be converted to ASN.1
$xml.Clear()
$xml.Tag = "sequence"
$xml.NewChild2("int",$r)
$xml.NewChild2("int",$s)

# Convert the XML to ASN.1
$success = $asn.LoadAsnXml($xml.GetXml())

# Emit the signature as DER encoded ASN.1 (base64)
$asnSig = $asn.GetEncodedDer("base64")

# --------------------------------------------------------------------
# Verify the signature using the asnSig we built from the r,s values
# --------------------------------------------------------------------

$dsa2 = New-Object Chilkat.Dsa

# Load the DSA public key to be used for verification:

$pemPublicKey = $dsa2.LoadText("qa_data/dsa/dsaPubKey2.pem")
$success = $dsa2.FromPublicPem($pemPublicKey)
if ($success -eq $false) {
    $($dsa2.LastErrorText)
    exit
}

# Load the hash to be verified.
$success = $dsa2.SetEncodedHash("hex",$hashStr)
if ($success -eq $false) {
    $($dsa2.LastErrorText)
    exit
}

# Load the ASN.1 signature:
$success = $dsa2.SetEncodedSignature("base64",$asnSig)
if ($success -eq $false) {
    $($dsa2.LastErrorText)
    exit
}

# Verify:
$success = $dsa2.Verify()
if ($success -eq $false) {
    $($dsa2.LastErrorText)
}
else {
    $("DSA Signature Verified!")
}