(Chilkat2-Python) Decrypt 256-bit AES GCM Produced by Something Unknown

Demonstrates how to decrypt something produced elsewhere (unknown) with 256-bit AES GCM.

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

import chilkat2

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

# We have the following to decrypt:

# Key (Base64): 
keyBase64 = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"

# IV (Base64Url):
ivBase64Url = "xrvaINMLqotAbWRK"

# ciphertext (base64url):
cipherBase64Url = "RtGNAS-zQOxSB8W0HfqJjCoyt9KgImW_l-HjVC40hOOl-RNfRF3hzDIT1kvFVF8i_KX9XmqAftb6lyq-jLCEc_MSgqt3q1ixv3Ez4SbS3G5e3qGzLwxIMi2sCt00aDNwK2ipsJ4aw8s7ePPnl4oY-y1st9rwCWR0rrgEZwS9jmS4uJWGPn9K3jbKRnMslznDbtFLNJctMVXBTP-cv47JelxLCBOQSlK29rMuEFrhHR_VQrPq6gtZaBVSXZSYT0XOklp7nu9mVhrMCRtBCC5oiu5MPE5JYx4ANo3hUY7_NyQl2bpn9GfRXrdvqRGE-gy2upj-cDkm0t_tV8xmYge9DBQTH3B_4BGl2qTk_o-m7pEmKkS8XSdQhGcuFlykqrkE8SzB5I8esfzWOM0pwxbz0H_VaylKYHY="

crypt = chilkat2.Crypt2()

crypt.CryptAlgorithm = "aes"
crypt.CipherMode = "gcm"
crypt.KeyLength = 256

success = crypt.SetEncodedAad("random","ascii")
crypt.SetEncodedKey(keyBase64,"base64")
crypt.SetEncodedIV(ivBase64Url,"base64url")

# The cipher text contains the 16-byte auth tag at the end.
# get it separately..
bdEncrypted = chilkat2.BinData()
bdAuthTag = chilkat2.BinData()
success = bdEncrypted.AppendEncoded(cipherBase64Url,"base64url")

numBytes = bdEncrypted.NumBytes
authTagHex = bdEncrypted.GetEncodedChunk(numBytes - 16,16,"hex")

print("Auth tag in hex: " + authTagHex)

success = bdAuthTag.AppendEncoded(authTagHex,"hex")
bdEncrypted.RemoveChunk(numBytes - 16,16)

# Use this special value to tell Chilkat to ignore the auth tag.
success = crypt.SetEncodedAuthTag("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF","hex")

# Decrypt
crypt.EncodingMode = "base64"
originalText = crypt.DecryptStringENC(bdEncrypted.GetEncoded("base64"))
if (crypt.LastMethodSuccess == False):
    print(crypt.LastErrorText)
else:
    print(originalText)
    print("Success.")

# Decrypted text