https://medium.com/@julien.maffre/what-is-an-ethereum-keystore-file-86c8c5917b97

web3-v3-keystore.py

import sha3
import hashlib
import scrypt
from binascii import unhexlify, hexlify
from Crypto.Cipher import AES
from Crypto.Util import Counter

data = {
  "address": "178ca94d1dece58a1c16bcb6e0eab8f440e60a01",
  "crypto": {
    "cipher": "aes-128-ctr",
    "ciphertext": "383cca818805e1134e93d200db94b9babc798e6537373604543ae870c1d221e2",
    "cipherparams": {
      "iv": "25e68fc8d166ee203c645868d5e0f94a"
    },
    "kdf": "scrypt",
    "kdfparams": {
      "dklen": 32,
      "n": 262144,
      "p": 1,
      "r": 8,
      "salt": "d27657804be7ef5b9c4d0ac513aa210eeb1ec64ad8f23d639aa579aebfc76832"
    },
    "mac": "75ec9139e21805983da2ca8f2523aec5bd78cf5983b93f1306b913e80fabdb7d"
  },
  "id": "5f20d562-5ab8-4c15-8df6-4ba8fbddacba",
  "version": 3
}

password = 'hello123'

def get_kdf_key(kdfparams, password):
    r = kdfparams['r']
    p = kdfparams['p']
    n = kdfparams['n']
    buflen = kdfparams['dklen']
    salt = unhexlify(kdfparams['salt'])
    return scrypt.hash(password, salt, N=n, r=r, p=p, buflen=buflen)   

def calc_mac(data, password):
    crypto = data['crypto']
    ciphertext = unhexlify(crypto['ciphertext'])
    kdfparams = crypto['kdfparams']
    decryption_key = get_kdf_key(kdfparams, password)
    print(hexlify(decryption_key[16:32] + ciphertext))
    calculated_mac = sha3.keccak_256(decryption_key[16:32] + ciphertext)
    return calculated_mac.digest()

mac_hex = hexlify(calc_mac(data, password))
print('mac = {}'.format(mac_hex))
print(mac_hex == data['crypto']['mac'])

def decrypt_key(data, password):
    crypto = data['crypto']
    ciphertext = unhexlify(crypto['ciphertext'])
    iv_hex = crypto['cipherparams']['iv']
    iv = unhexlify(iv_hex)
    decryption_key = get_kdf_key(crypto['kdfparams'], password)
    ctr = Counter.new(128, initial_value=long(iv_hex, 16))
    aes = AES.new(decryption_key[:16], AES.MODE_CTR, counter=ctr)
    return aes.decrypt(ciphertext)

print('privkey = {}'.format(hexlify(decrypt_key(data, password))))

def encrypt_key(privkey_hex, iv_hex, kdfparams, password):
    privkey_bytes = unhexlify(privkey_hex)
    iv = unhexlify(iv_hex)
    decryption_key = get_kdf_key(kdfparams, password)
    ctr = Counter.new(128, initial_value=long(iv_hex, 16))
    aes = AES.new(decryption_key[:16], AES.MODE_CTR, counter=ctr)
    return aes.encrypt(privkey_bytes)
    
privkey_hex = '2d319aff207c5b566af776a3e59dfda994e538baa239c81ffa4f780759d3fbe8'
iv_hex = '25e68fc8d166ee203c645868d5e0f94a'
kdfparams = data['crypto']['kdfparams']
output_ciphertext = hexlify(encrypt_key(privkey_hex, iv_hex, kdfparams, password))
print('ciphertext = {}'.format(output_ciphertext))
print(output_ciphertext == '383cca818805e1134e93d200db94b9babc798e6537373604543ae870c1d221e2')