CkPython

Verify an RSA Signature Against the Signed String

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Demonstrates how to validate an RSA Signature against the string that was signed. CkPython

import sys
import chilkat

success = False

# Create the same string we previously signed in this example: 
# RSA Sign utf-8 Bytes of String to get Base64 RSA Signature

sb = chilkat.CkStringBuilder()
crlfLineEnding = True

for i in range(0,11):
    sb.AppendLine("This is a test.",crlfLineEnding)

base64_rsa_sig = "gWgpEXQqvXN6wh0MuFXPiw2xCb8cnmdizBT1TD1Tpm2GlJ8gnD59DGSj35GGXk1tM+mCOvMa2uW/9gmz8p6A90JLbn918i/2wKGvcde4wXnzPO7JADSNn2UwYzf3rp4/q/JrHv1GZETRJhABSFqTxOgdmdbEJQE/zijOSctCtQAM2CTb6t2BO8uHKSSUAwPH2cbeWxqsaVRLT4ruk5nZOxhoLgLMSjupiSzbE8zSTkkFOEHD+Mbb2xwg85AI0E4DsUnp+hLwwtS0blesgSyvtBY8oJODJeFcJsR7JDOTPdzHQHgJRl/2A4ij5xT91TpXy7ok43jhT6O9j7Q3qrafIQ=="

# Get the public key to be used for signature verification.
pubKey = chilkat.CkPublicKey()
success = pubKey.LoadFromFile("rsaKeys/chilkat-rsa-2048.pem")
if (success == False):
    print(pubKey.lastErrorText())
    sys.exit()

rsa = chilkat.CkRsa()
success = rsa.UsePublicKey(pubKey)
if (success == False):
    print(rsa.lastErrorText())
    sys.exit()

# Verify the string against the signature.
# We signed the utf-8 byte representation of the string, so we must indicate
# to also validate against the utf-8 byte representation.
rsa.put_Charset("utf-8")
rsa.put_EncodingMode("base64")
signedString = sb.getAsString()
success = rsa.VerifyStringENC(signedString,"sha256",base64_rsa_sig)

if (success == False):
    print(rsa.lastErrorText())
    print("Signature invalid.")
else:
    print("Signature valid.")