(CkPython) DSA Signature Create and Verify

Shows how to create a DSA (DSS) signature for the contents of a file. The first step is to create an SHA-1 hash of the file contents. The hash is signed using the Digital Signature Algorithm and the signature bytes are retrieved as a hex-encoded string.

The 2nd part of the example loads the signature and verifies it against the hash.

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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")

# Return the SHA-1 hash of a file.  The file may be any size.
# The Chilkat Crypt component will stream the file when 
# computing the hash, keeping the memory usage constant
# and reasonable.
# The 20-byte SHA-1 hash is returned as a hex-encoded string.
hashStr = crypt.hashFileENC("hamlet.xml")

dsa = chilkat.CkDsa()

# Load a DSA private key from a PEM file.  Chilkat DSA
# provides the ability to load and save DSA public and private
# keys from encrypted or non-encrypted PEM or DER.
# The LoadText method is for convenience only.  You may
# use any means to load the contents of a PEM file into
# a string.

pemPrivateKey = dsa.loadText("dsa_priv.pem")
success = dsa.FromPem(pemPrivateKey)
if (success != True):
    print(dsa.lastErrorText())
    sys.exit()

# You may optionally verify the key to ensure that it is a valid
# DSA key.
success = dsa.VerifyKey()
if (success != True):
    print(dsa.lastErrorText())
    sys.exit()

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

# Now that the DSA object contains both the private key and hash,
# it is ready to create the signature:
success = dsa.SignHash()
if (success != True):
    print(dsa.lastErrorText())
    sys.exit()

# If SignHash is successful, the DSA object contains the
# signature.  It may be accessed as a hex or base64 encoded
# string.  (It is also possible to access directly in byte array form via
# the "Signature" property.)
hexSig = dsa.getEncodedSignature("hex")
print("Signature:")
print(hexSig)

# -----------------------------------------------------------
# Step 2: Verify the DSA Signature
# -----------------------------------------------------------

dsa2 = chilkat.CkDsa()

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

pemPublicKey = dsa2.loadText("dsa_pub.pem")
success = dsa2.FromPublicPem(pemPublicKey)
if (success != True):
    print(dsa2.lastErrorText())
    sys.exit()

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

# Load the signature:
success = dsa2.SetEncodedSignature("hex",hexSig)
if (success != True):
    print(dsa2.lastErrorText())
    sys.exit()

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