(Lianja) 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.

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

loCrypt = createobject("CkCrypt2")

// 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.)
loPfx = createobject("CkPfx")
llSuccess = loPfx.LoadPfxFile("qa_data/rsassa-pss/privatekey.pfx","PFX_PASSWORD")
if (llSuccess <> .T.) then
    ? loPfx.LastErrorText
    release loCrypt
    release loPfx
    return
endif

// 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.)
loCert = loPfx.GetCert(0)
if (loPfx.LastMethodSuccess <> .T.) then
    ? loPfx.LastErrorText
    release loCrypt
    release loPfx
    return
endif

loCrypt.SetSigningCert(loCert)

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

loCrypt.EncodingMode = "base64"

// Sign a string and return the base64 PKCS7 detached signature
lcOriginalText = "This is a test"
lcPkcs7sig = loCrypt.SignStringENC(lcOriginalText)
? "Detached Signature:"
? lcPkcs7sig

// 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:
llSuccess = loCrypt.VerifyStringENC(lcOriginalText,lcPkcs7sig)
? "Signature verified: " + str(llSuccess)
llSuccess = loCrypt.VerifyStringENC("Not the original text",lcPkcs7sig)
? "Signature verified: " + str(llSuccess)

// 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.
lcOpaqueSig = loCrypt.OpaqueSignStringENC(lcOriginalText)
? "Opaque Signature:"
? lcOpaqueSig

// 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:
lcOrigTxt = loCrypt.OpaqueVerifyStringENC(lcOpaqueSig)
if (loCrypt.LastMethodSuccess <> .T.) then
    ? "Signature verification failed."
    ? loCrypt.LastErrorText
    release loCert
    release loCrypt
    release loPfx
    return
endif

? "Signature verified."
? "Extracted text:" + lcOrigTxt

release loCert


release loCrypt
release loPfx