(PowerShell) DSA Signature Create and Verify

Shows how to create a DSA (DSS) signature for the contents of a file. The first step is to create an SHA-1 hash of the file contents. The hash is signed using the Digital Signature Algorithm and the signature bytes are retrieved as a hex-encoded string.

The 2nd part of the example loads the signature and verifies it against the hash.

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.

$crypt = New-Object Chilkat.Crypt2

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

# Return the SHA-1 hash of a file.  The file may be any size.
# The Chilkat Crypt component will stream the file when 
# computing the hash, keeping the memory usage constant
# and reasonable.
# The 20-byte SHA-1 hash is returned as a hex-encoded string.
$hashStr = $crypt.HashFileENC("hamlet.xml")

$dsa = New-Object Chilkat.Dsa

# Load a DSA private key from a PEM file.  Chilkat DSA
# provides the ability to load and save DSA public and private
# keys from encrypted or non-encrypted PEM or DER.
# The LoadText method is for convenience only.  You may
# use any means to load the contents of a PEM file into
# a string.

$pemPrivateKey = $dsa.LoadText("dsa_priv.pem")
$success = $dsa.FromPem($pemPrivateKey)
if ($success -ne $true) {
    $($dsa.LastErrorText)
    exit
}

# You may optionally verify the key to ensure that it is a valid
# DSA key.
$success = $dsa.VerifyKey()
if ($success -ne $true) {
    $($dsa.LastErrorText)
    exit
}

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

# Now that the DSA object contains both the private key and hash,
# it is ready to create the signature:
$success = $dsa.SignHash()
if ($success -ne $true) {
    $($dsa.LastErrorText)
    exit
}

# If SignHash is successful, the DSA object contains the
# signature.  It may be accessed as a hex or base64 encoded
# string.  (It is also possible to access directly in byte array form via
# the "Signature" property.)
$hexSig = $dsa.GetEncodedSignature("hex")
$("Signature:")
$($hexSig)

# -----------------------------------------------------------
# Step 2: Verify the DSA Signature
# -----------------------------------------------------------

$dsa2 = New-Object Chilkat.Dsa

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

$pemPublicKey = $dsa2.LoadText("dsa_pub.pem")
$success = $dsa2.FromPublicPem($pemPublicKey)
if ($success -ne $true) {
    $($dsa2.LastErrorText)
    exit
}

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

# Load the signature:
$success = $dsa2.SetEncodedSignature("hex",$hexSig)
if ($success -ne $true) {
    $($dsa2.LastErrorText)
    exit
}

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