def derive_key_and_iv(password, salt, key_length, iv_length):
    d = d_i = ''
    while len(d) < key_length + iv_length:
        d_i = md5(d_i + password + salt).digest()
        d += d_i
    return d[:key_length], d[key_length:key_length+iv_length]
def encrypt(in_file, out_file, password, key_length=32):
    bs = AES.block_size
    salt = Random.new().read(bs - len('Salted__'))
    key, iv = derive_key_and_iv(password, salt, key_length, bs)
    cipher = AES.new(key, AES.MODE_CBC, iv)
    out_file.write('Salted__' + salt)
    finished = False
    while not finished:
        chunk = in_file.read(1024 * bs)
        if len(chunk) == 0 or len(chunk) % bs != 0:
            padding_length = (bs - len(chunk) % bs) or bs
            chunk += padding_length * chr(padding_length)
            finished = True
        out_file.write(cipher.encrypt(chunk))
def decrypt(in_file, out_file, password, key_length=32):
    bs = AES.block_size
    print(bs)
    salt = in_file.read(bs)[len('Salted__'):]
    key, iv = derive_key_and_iv(password, salt, key_length, bs)
    cipher = AES.new(key, AES.MODE_CBC, iv)
    next_chunk = ''
    finished = False
    while not finished:
        chunk, next_chunk = next_chunk, cipher.decrypt(in_file.read(1024 * bs))
        if len(next_chunk) == 0:
            padding_length = ord(chunk[-1])
            chunk = chunk[:-padding_length]
            finished = True
        out_file.write(chunk)

package main
import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"encoding/base64"
	"errors"
	"fmt"
	"io"
	"log"
	"crypto/md5"
	"os"
)
func pyEncrypt(password []byte, pathToInFile string, pathToOutFile string) {
	bs := int(aes.BlockSize)
	salt := make([]byte, aes.BlockSize-len("Salted__"))
	_, err := rand.Read(salt)
	if err != nil {
		panic(err)
	}
	key, iv := deriveKeyAndIV(password, salt, bs)
	block, err := aes.NewCipher(key)
	if err != nil {
		panic(err)
	}
	cfb := cipher.NewCFBEncrypter(block, iv)
	fin, err := os.Open(pathToInFile)
	if err != nil {
		panic(err)
	}
	defer fin.Close()
	fout, err := os.Create(pathToOutFile)
	if err != nil {
		panic(err)
	}
	defer fout.Close()
	_, err = fout.Write([]byte("Salted__"))
	if err != nil {
		panic(err)
	}
	_, err = fout.Write(salt)
	if err != nil {
		panic(err)
	}
	for true {
		ciphertext := make([]byte, 1024*bs)
		chunk := make([]byte, 1024*bs)
		_, err := fin.Read(chunk)
		if err == io.EOF {
			break
		} else if err != nil {
			panic(err)
		}
		cfb.XORKeyStream(ciphertext, chunk)
		fout.Write(ciphertext)
	}
}
func deriveKeyAndIV(password []byte, salt []byte, bs int) ([]byte, []byte) {
	var digest []byte
	hash := md5.New()
	out := make([]byte, 32+bs) //right now I'm just matching the default key size (32) from the python script so 32 represents the default from python
	for i := 0; i < 32+bs; i += len(digest) {
		hash.Reset()
		hash.Write(digest)
		hash.Write(password)
		hash.Write(salt)
		digest = hash.Sum(digest[:0])
		copy(out[i:], digest)
	}
	return out[:32], out[32:32+bs] //matching the default key size from Python as that is what the application uses
}
func main() {
	pwd := []byte("test123")
	pyEncrypt(pwd, "/home/chris/pt.txt", "/home/chris/genc.txt")
}

func pyEncrypt(password string, pathToInFile string, pathToOutFile string){
    bs := int(aes.BlockSize)
    salt := make([]byte, aes.BlockSize - len("Salted__")) 
    _, err := rand.Read(salt)
    if err != nil {panic(err)}
    key, iv := deriveKeyAndIV([]byte(password), salt, bs)    
    block, err := aes.NewCipher(key)
    if err != nil {panic(err)}
    
    cbc := cipher.NewCBCEncrypter(block, iv)
    fin, err := os.Open(pathToInFile)
    if err != nil {panic(err)}
    defer fin.Close()
    
    fout, err := os.Create(pathToOutFile)
    if err != nil {panic(err)}
    defer fout.Close()
    
    _,err = fout.Write([]byte("Salted__"))
    if err != nil {panic(err)}
    _,err = fout.Write(salt)
    if err != nil {panic(err)}
    
    for true{
        chunk := make([]byte, 1024 * bs)
                
        n,err := fin.Read(chunk)
        if err == io.EOF{
        break
        }else if err != nil{
            panic(err)
        }
        
        if n == 0 || n % bs != 0 {//need to pad up to block size :bs
            paddingLength := (bs - n % bs) 
            paddingChr := []byte(string(rune(paddingLength)))
            paddingBytes := make([]byte, paddingLength)
            
            for i := 0; i < paddingLength; i++{
                paddingBytes[i] = paddingChr[0]
            }
            
            chunk = append(chunk[0:n], []byte(paddingBytes)...)
        }else{
            chunk = chunk[0:n]//no padding needed            
        }
        
        ciphertext := make([]byte, len(chunk))
        cbc.CryptBlocks(ciphertext,chunk)
        fout.Write(ciphertext)
    }
}