PowerShell

Verify an RSA Signature Against the Signed String

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Demonstrates how to validate an RSA Signature against the string that was signed. PowerShell

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

$success = $false

# Create the same string we previously signed in this example: 
# RSA Sign utf-8 Bytes of String to get Base64 RSA Signature

$sb = New-Object Chilkat.StringBuilder
$crlfLineEnding = $true

for ($i = 0; $i -le 10; $i++) {
    $sb.AppendLine("This is a test.",$crlfLineEnding)
}

$base64_rsa_sig = "gWgpEXQqvXN6wh0MuFXPiw2xCb8cnmdizBT1TD1Tpm2GlJ8gnD59DGSj35GGXk1tM+mCOvMa2uW/9gmz8p6A90JLbn918i/2wKGvcde4wXnzPO7JADSNn2UwYzf3rp4/q/JrHv1GZETRJhABSFqTxOgdmdbEJQE/zijOSctCtQAM2CTb6t2BO8uHKSSUAwPH2cbeWxqsaVRLT4ruk5nZOxhoLgLMSjupiSzbE8zSTkkFOEHD+Mbb2xwg85AI0E4DsUnp+hLwwtS0blesgSyvtBY8oJODJeFcJsR7JDOTPdzHQHgJRl/2A4ij5xT91TpXy7ok43jhT6O9j7Q3qrafIQ=="

# Get the public key to be used for signature verification.
$pubKey = New-Object Chilkat.PublicKey
$success = $pubKey.LoadFromFile("rsaKeys/chilkat-rsa-2048.pem")
if ($success -eq $false) {
    $($pubKey.LastErrorText)
    exit
}

$rsa = New-Object Chilkat.Rsa
$success = $rsa.UsePublicKey($pubKey)
if ($success -eq $false) {
    $($rsa.LastErrorText)
    exit
}

# Verify the string against the signature.
# We signed the utf-8 byte representation of the string, so we must indicate
# to also validate against the utf-8 byte representation.
$rsa.Charset = "utf-8"
$rsa.EncodingMode = "base64"
$signedString = $sb.GetAsString()
$success = $rsa.VerifyStringENC($signedString,"sha256",$base64_rsa_sig)

if ($success -eq $false) {
    $($rsa.LastErrorText)
    $("Signature invalid.")
}
else {
    $("Signature valid.")
}