(C# UWP/WinRT) RSASSA-PSS Sign String to Create Base64 PCKS7 Signature

Signs a string to create a PKCS7 signature in the base64 encoding. The signature algorithm is RSASSA-PSS with SHA256.

Note: This example requires Chilkat v9.5.0.67 or greater.

Chilkat Universal Windows Platform (UWP) / WinRT Downloads Chilkat for the Universal Windows Platform (UWP)

// This example requires the Chilkat Crypt API to have been previously unlocked.
// See Unlock Chilkat Crypt for sample code.

Chilkat.Crypt2 crypt = new Chilkat.Crypt2();

// Get a digital certificate with private key from a .pfx
// (Chilkat has many different ways to provide a cert + private key for siging.
// Using a PFX is just one possible option.)
Chilkat.Pfx pfx = new Chilkat.Pfx();
bool success = pfx.LoadPfxFile("qa_data/rsassa-pss/privatekey.pfx","PFX_PASSWORD");
if (success != true) {
    Debug.WriteLine(pfx.LastErrorText);
    return;
}

// Get the certificate to be used for signing.
// (The typical case for a PFX is that it contains a cert with an associated private key,
// as well as other certificates in the chain of authentication.  The cert with the private
// key should be in the first position at index 0.)
Chilkat.Cert cert = pfx.GetCert(0);
if (pfx.LastMethodSuccess != true) {
    Debug.WriteLine(pfx.LastErrorText);
    return;
}

crypt.SetSigningCert(cert);

// Indicate that RSASSA-PSS with SHA256 should be used.
crypt.SigningAlg = "pss";
crypt.HashAlgorithm = "sha256";

crypt.EncodingMode = "base64";

// Sign a string and return the base64 PKCS7 detached signature
string originalText = "This is a test";
string pkcs7sig = await crypt.SignStringENCAsync(originalText);
Debug.WriteLine("Detached Signature:");
Debug.WriteLine(pkcs7sig);

// This signature looks like this:
// MIIG5wYJKoZIhvcNAQcCoIIG2DCCBtQCAQExDzANBgl .. YToLqEwTdU87ox5g7rvw==

// The ASN.1 of the signature can be examined by browsing to https://lapo.it/asn1js/ ,
// then copy-and-paste the Base64 signature into the form and decode..

// The signature can be verified against the original data like this:
success = crypt.VerifyStringENC(originalText,pkcs7sig);
Debug.WriteLine("Signature verified: " + Convert.ToString(success));
success = crypt.VerifyStringENC("Not the original text",pkcs7sig);
Debug.WriteLine("Signature verified: " + Convert.ToString(success));

// Now we'll create an opaque signature (the opposite of a detached signature). 
// An opaque signature is a PKCS7 message that contains both the original data and
// the signature.  The verification process extracts the original data.
string opaqueSig = await crypt.OpaqueSignStringENCAsync(originalText);
Debug.WriteLine("Opaque Signature:");
Debug.WriteLine(opaqueSig);

// The ASN.1 of the signature can be examined by browsing to https://lapo.it/asn1js/ ,
// then copy-and-paste the Base64 signature into the form and decode..

// We can verify and extract the original data:
string origTxt = crypt.OpaqueVerifyStringENC(opaqueSig);
if (crypt.LastMethodSuccess != true) {
    Debug.WriteLine("Signature verification failed.");
    Debug.WriteLine(crypt.LastErrorText);

    return;
}

Debug.WriteLine("Signature verified.");
Debug.WriteLine("Extracted text:" + origTxt);