(Chilkat2-Python) ECDSA Sign Data and Get Raw R and S Values

Demonstrates getting the raw R and S value of an ECDSA signature.

Chilkat2 Python Downloads install with pip pip3 install chilkat2 or download... Python Module for Windows, Linux, Alpine Linux, MacOS, Solaris

import sys
import chilkat2

# 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.

crypt = chilkat2.Crypt2()
crypt.HashAlgorithm = "SHA256"
crypt.Charset = "utf-8"
crypt.EncodingMode = "base64"

# Hash a string.
hash1 = crypt.HashStringENC("The quick brown fox jumps over the lazy dog")
print("hash1 = " + hash1)

# -----------------------------------------------------------
# An ECDSA private key is used for signing.  The public key is for signature verification.
# Load our ECC private key.
# Our private key file contains this:

# 	// -----BEGIN PRIVATE KEY-----
# 	MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQg3J8q/24D1sEKGdP9
# 	72MGYElLGpw/a56Y3t6pfON3uhShRANCAATlSmoizyhAwoYZAOuFBATl07/1RR54
# 	a1Dzfm16grxJe666AGKR+bSs24hk7TEpaeCTvT8YOOM3l+xKFg7zq6Q9
# 	-----END PRIVATE KEY-----

privKey = chilkat2.PrivateKey()
success = privKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem")
if (success != True):
    print(privKey.LastErrorText)
    sys.exit()

# Sign the hash..
prng = chilkat2.Prng()
ecdsa = chilkat2.Ecc()
ecdsaSigBase64 = ecdsa.SignHashENC(hash1,"base64",privKey,prng)
if (ecdsa.LastMethodSuccess != True):
    print(ecdsa.LastErrorText)
    sys.exit()

# The ECDSA signature is ASN.1 that contains a sequence of 2 large integers (r and s)
# For example:
# SEQUENCE (2 elem)
#   INTEGER (255 bit) 792134D9B4AD82D5431ED03835A88E2596EB35E5B13054BD9B05A0069281ACC9
#   INTEGER (255 bit) 481E758CC1E3CBF825537EC3D9A2CA627E5FAD1137BBEA65DF38658DCB0A9ED5

print("Base64 ECDSA signature = " + ecdsaSigBase64)

# If the raw R and S values are needed, here's how to get them:
asn = chilkat2.Asn()
success = asn.LoadEncoded(ecdsaSigBase64,"base64")
if (success == False):
    print(asn.LastErrorText)
    sys.exit()

# The R and X will be in hexidecimal in the XML.
xml = chilkat2.Xml()
xml.LoadXml(asn.AsnToXml())
print(xml.GetXml())

# The XML looks like this:
# <sequence>
# <int>792134D9B4AD82D5431ED03835A88E2596EB35E5B13054BD9B05A0069281ACC9</int>
# <int>481E758CC1E3CBF825537EC3D9A2CA627E5FAD1137BBEA65DF38658DCB0A9ED5</int>
# </sequence>

# Copy raw R and S hex values into a Chilkat BinData object.
bd = chilkat2.BinData()
r = xml.GetChildContent("int[0]")
s = xml.GetChildContent("int[1]")
bd.AppendEncoded(r,"hex")
bd.AppendEncoded(s,"hex")

print("Number of bytes in bd: " + str(bd.NumBytes))