(Python) Get a Certificate's Key Size

Demonstrates how to get the RSA key size of a certificate (for example, 1024-bit, 2048-bit, etc.)

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

import sys
import chilkat

#  For this example, I have a certificate in raw base64 format (not PEM),
#  that looks like this:  "MIIGkDCCBHigAwIBAgIUMDA ... s/iqLsLA=="
sbCertBase64 = chilkat.CkStringBuilder()
success = sbCertBase64.LoadFile("qa_data/certs/base64Cert.txt","utf-8")

cert = chilkat.CkCert()
success = cert.LoadFromBase64(sbCertBase64.getAsString())
if (success != True):
    print(cert.lastErrorText())
    sys.exit()

#  Get the public key.
# pubKey is a CkPublicKey
pubKey = cert.ExportPublicKey()
if (cert.get_LastMethodSuccess() != True):
    print(cert.lastErrorText())
    sys.exit()

#  In Chilkat version v9.5.0.67, the KeySize property was added.
numBits = pubKey.get_KeySize()
print("Number of bits = " + str(numBits))

#  If using an older version of Chilkat, the key size can be obtained like this:
xml = chilkat.CkXml()
xml.LoadXml(pubKey.getXml())

binDat = chilkat.CkBinData()
binDat.AppendEncoded(xml.getChildContent("Modulus"),"base64")

numBits = 8 * binDat.get_NumBytes()
print("Number of bits = " + str(numBits))