(CkPython) DSA R,S Signature Values

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Creates a DSA signature. Gets r,s values from the signature. Re-creates the DSA signature ASN.1 from the r,s values. Then verifies the signature using the re-created ASN.1 DSA signature.

Chilkat Python Downloads install with pip pip3 install chilkat or download... Python Module for Windows, MacOS, Linux, Alpine Linux, Solaris

import sys
import chilkat

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

crypt = chilkat.CkCrypt2()

crypt.put_EncodingMode("hex")
crypt.put_HashAlgorithm("sha-1")

hashStr = crypt.hashFileENC("qa_data/hamlet.xml")
print("hash to sign: " + hashStr)

dsa = chilkat.CkDsa()

pemPrivateKey = dsa.loadText("qa_data/dsa/dsaPrivKey2.pem")
success = dsa.FromPem(pemPrivateKey)
if (success == False):
    print(dsa.lastErrorText())
    sys.exit()

# Load the hash to be signed into the DSA object:
success = dsa.SetEncodedHash("hex",hashStr)
if (success == False):
    print(dsa.lastErrorText())
    sys.exit()

# Sign the hash.
success = dsa.SignHash()
if (success == False):
    print(dsa.lastErrorText())
    sys.exit()

# Get the ASN.1 signature.
asnSig = dsa.getEncodedSignature("base64")
print("Signature: " + asnSig)

# Examine the details of the ASN.1 signature.
# We want to get the r,s values as hex strings..
asn = chilkat.CkAsn()
success = asn.LoadEncoded(asnSig,"base64")
if (success == False):
    print(asn.lastErrorText())
    sys.exit()

# Get the ASN.1 as XML.
xml = chilkat.CkXml()
success = xml.LoadXml(asn.asnToXml())
print("Signature as XML: ")
print(xml.getXml())

# Sample XML shown here.
# The r and s values are the two hex strings in the XML.

# <?xml version="1.0" encoding="utf-8"?>
# <sequence>
#     <int>2C187F3AB6E47A66497B86CE97BB39E2133810F5</int>
#     <int>588E53D3F7B69636B48FD7175E99A3961BD7D775</int>
# </sequence>

# Pretend we're starting with r,s
r = "2C187F3AB6E47A66497B86CE97BB39E2133810F5"
s = "588E53D3F7B69636B48FD7175E99A3961BD7D775"

# Build the XML that will be converted to ASN.1
xml.Clear()
xml.put_Tag("sequence")
xml.NewChild2("int",r)
xml.NewChild2("int",s)

# Convert the XML to ASN.1
success = asn.LoadAsnXml(xml.getXml())

# Emit the signature as DER encoded ASN.1 (base64)
asnSig = asn.getEncodedDer("base64")

# --------------------------------------------------------------------
# Verify the signature using the asnSig we built from the r,s values
# --------------------------------------------------------------------

dsa2 = chilkat.CkDsa()

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

pemPublicKey = dsa2.loadText("qa_data/dsa/dsaPubKey2.pem")
success = dsa2.FromPublicPem(pemPublicKey)
if (success == False):
    print(dsa2.lastErrorText())
    sys.exit()

# Load the hash to be verified.
success = dsa2.SetEncodedHash("hex",hashStr)
if (success == False):
    print(dsa2.lastErrorText())
    sys.exit()

# Load the ASN.1 signature:
success = dsa2.SetEncodedSignature("base64",asnSig)
if (success == False):
    print(dsa2.lastErrorText())
    sys.exit()

# Verify:
success = dsa2.Verify()
if (success == False):
    print(dsa2.lastErrorText())
else:
    print("DSA Signature Verified!")