CkPython

Create ECSDA Signature using Raw r and s Format (not ASN.1)

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Demonstrates how to create an ECDSA signature using the raw r/s format.

ECDSA signatures have two equal sized parts, r and s. There are two common formats for encoding the signature:

(a) Concatenating the raw byte array of r and s
(b) Encoding both into a structured ASN.1 / DER sequence.

This example demonstrates how to create a signature that is a byte array of r and s concatenated.

Note: This example requires Chilkat v9.5.0.97 or greater.

CkPython

import sys
import chilkat

success = False

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

# To create an ECDSA signature, the data first needs to be hashed.  Then the hash
# is signed.

sb = chilkat.CkStringBuilder()
sb.Append("The quick brown fox jumps over the lazy dog")
hash = sb.getHash("sha256","base64","utf-8")

# Load the ECDSA key to be used for signing.
privKey = chilkat.CkPrivateKey()
success = privKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem")
if (success != True):
    print(privKey.lastErrorText())
    sys.exit()

prng = chilkat.CkPrng()
ecdsa = chilkat.CkEcc()

# Produce a signature that is not ASN.1, but is instead the concatenation
# of the raw r and s signature parts.
# This feature was added in Chilkat v9.5.0.97
ecdsa.put_AsnFormat(False)

ecdsaSigBase64 = ecdsa.signHashENC(hash,"base64",privKey,prng)
if (ecdsa.get_LastMethodSuccess() != True):
    print(ecdsa.lastErrorText())
    sys.exit()

print("ECDSA signature = " + ecdsaSigBase64)

# -----------------------------------------------------------
# Now let's verify the signature using the public key.

pubKey = chilkat.CkPublicKey()
success = pubKey.LoadFromFile("qa_data/ecc/secp256r1-pubkey.pem")
if (success != True):
    print(pubKey.lastErrorText())
    sys.exit()

# Note: When verifying, Chilkat will auto-detect the format for both kinds of ECDSA signatures (ASN.1 or binary r+s)
result = ecdsa.VerifyHashENC(hash,ecdsaSigBase64,"base64",pubKey)
if (result == 1):
    print("Signature is valid.")
    sys.exit()

if (result == 0):
    print("Signature is invalid.")
    sys.exit()

if (result < 0):
    print(ecdsa.lastErrorText())
    print("The VerifyHashENC method call failed.")
    sys.exit()