(Chilkat2-Python) 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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import sys
import chilkat2

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

crypt = chilkat2.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.)
pfx = chilkat2.Pfx()
success = pfx.LoadPfxFile("qa_data/rsassa-pss/privatekey.pfx","PFX_PASSWORD")
if (success != True):
    print(pfx.LastErrorText)
    sys.exit()

# 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.)
# cert is a CkCert
cert = pfx.GetCert(0)
if (pfx.LastMethodSuccess != True):
    print(pfx.LastErrorText)
    sys.exit()

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
originalText = "This is a test"
pkcs7sig = crypt.SignStringENC(originalText)
print("Detached Signature:")
print(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)
print("Signature verified: " + str(success))
success = crypt.VerifyStringENC("Not the original text",pkcs7sig)
print("Signature verified: " + str(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.
opaqueSig = crypt.OpaqueSignStringENC(originalText)
print("Opaque Signature:")
print(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:
origTxt = crypt.OpaqueVerifyStringENC(opaqueSig)
if (crypt.LastMethodSuccess != True):
    print("Signature verification failed.")
    print(crypt.LastErrorText)

    sys.exit()

print("Signature verified.")
print("Extracted text:" + origTxt)