Decrypt aes encrypted file in java sha1 openssl

Question

Im trying to implement file decryption by referring this code:

Encryption part i have done this way: https//stackoverflow.com/questions/64423926/encrypt-file-in-java-and-

Answer 1

The below code is doing a complete file encryption and decryption and is compatible to the OpenSSL commands

encrypt: openssl enc -aes-256-cbc -pass pass:testpass -d -p -in plaintext.txt -out plaintext.txt.crypt -md md5
decrypt: openssl aes-256-cbc -d -in plaintext.txt.crypt -out plaintext1.txt -k testpass -md md5

I left out some variables as they are not used in decryption method and on the other hand substituded the byte[] concatination with a pure Java version.

The simple output is:

encrypt done plaintext.txt
ciphertext: plaintext.txt
Decrypt is completed

Security warning: the key derivation is DEPRECATED and should not used any longer. The code does not have any exception handling and is for educational purpose only.

code:

import javax.crypto.Cipher;
import javax.crypto.CipherOutputStream;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.security.*;
import java.util.Arrays;

public class MainSo {
    public static void main(String[] args) {
        System.out.println("https://stackoverflow.com/questions/64443373/decrypt-aes-encrypted-file-in-java-sha1-openssl?noredirect=1#comment113960588_64443373");
        String plaintextFilename = "plaintext.txt";
        String ciphertextFilename = "plaintext.txt.crypt";
        String decryptedtextFilename = "plaintextDecrypted.txt";
        String password = "testpass";

        // openssl equivalent:
        // decrypt: openssl aes-256-cbc -d -in plaintext.txt.crypt -out plaintext1.txt -k testpass -md md5
        // encrypt: openssl enc -aes-256-cbc -pass pass:testpass -d -p -in sample.crypt -out sample.txt -md md5

        String ciphertext = encryptfile(plaintextFilename, password);
        System.out.println("ciphertext: " + ciphertext);
        decryptNew(ciphertextFilename, password, decryptedtextFilename);
    }

    public static String encryptfile(String path, String password) {
        try {
            FileInputStream fis = new FileInputStream(path);
            FileOutputStream fos = new FileOutputStream(path.concat(".crypt"));
            final byte[] pass = password.getBytes(StandardCharsets.UTF_8);
            final byte[] salt = (new SecureRandom()).generateSeed(8);
            fos.write("Salted__".getBytes(StandardCharsets.UTF_8));
            fos.write(salt);
            final byte[] passAndSalt = concatenateByteArrays(pass, salt);
            byte[] hash = new byte[0];
            byte[] keyAndIv = new byte[0];
            for (int i = 0; i < 3 && keyAndIv.length < 48; i++) {
                final byte[] hashData = concatenateByteArrays(hash, passAndSalt);
                final MessageDigest md = MessageDigest.getInstance("MD5");
                hash = md.digest(hashData);
                keyAndIv = concatenateByteArrays(keyAndIv, hash);
            }
            final byte[] keyValue = Arrays.copyOfRange(keyAndIv, 0, 32);
            final byte[] iv = Arrays.copyOfRange(keyAndIv, 32, 48);
            final SecretKeySpec key = new SecretKeySpec(keyValue, "AES");
            final Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
            cipher.init(Cipher.ENCRYPT_MODE, key, new IvParameterSpec(iv));
            CipherOutputStream cos = new CipherOutputStream(fos, cipher);
            int b;
            byte[] d = new byte[8];
            while ((b = fis.read(d)) != -1) {
                cos.write(d, 0, b);
            }
            cos.flush();
            cos.close();
            fis.close();
            System.out.println("encrypt done " + path);
        } catch (IOException | NoSuchAlgorithmException | NoSuchPaddingException | InvalidKeyException | InvalidAlgorithmParameterException e) {
            e.printStackTrace();
        }
        return path;
    }

    static void decryptNew(String path,String password, String outPath) {
        byte[] SALTED_MAGIC = "Salted__".getBytes(StandardCharsets.UTF_8);
        try{
            FileInputStream fis = new FileInputStream(path);
            FileOutputStream fos = new FileOutputStream(outPath);
            final byte[] pass = password.getBytes(StandardCharsets.US_ASCII);
            final byte[] inBytes = Files.readAllBytes(Paths.get(path));
            final byte[] shouldBeMagic = Arrays.copyOfRange(inBytes, 0, SALTED_MAGIC.length);
            if (!Arrays.equals(shouldBeMagic, SALTED_MAGIC)) {
                throw new IllegalArgumentException("Initial bytes from input do not match OpenSSL SALTED_MAGIC salt value.");
            }
            final byte[] salt = Arrays.copyOfRange(inBytes, SALTED_MAGIC.length, SALTED_MAGIC.length + 8);
            final byte[] passAndSalt = concatenateByteArrays(pass, salt);
            byte[] hash = new byte[0];
            byte[] keyAndIv = new byte[0];
            for (int i = 0; i < 3 && keyAndIv.length < 48; i++) {
                final byte[] hashData = concatenateByteArrays(hash, passAndSalt);
                MessageDigest md = null;
                md = MessageDigest.getInstance("MD5");
                hash = md.digest(hashData);
                keyAndIv = concatenateByteArrays(keyAndIv, hash);
            }
            final byte[] keyValue = Arrays.copyOfRange(keyAndIv, 0, 32);
            final SecretKeySpec key = new SecretKeySpec(keyValue, "AES");
            final byte[] iv = Arrays.copyOfRange(keyAndIv, 32, 48);
            final Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
            cipher.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(iv));
            final byte[] clear = cipher.doFinal(inBytes, 16, inBytes.length - 16);
            String contentDecoded = new String(clear, StandardCharsets.UTF_8);
            fos.write(contentDecoded.getBytes());
            fos.close();
            System.out.println("Decrypt is completed");
        }catch(Exception e){
            e.printStackTrace();
        }
    }

    public static byte[] concatenateByteArrays(byte[] a, byte[] b) {
        return ByteBuffer
                .allocate(a.length + b.length)
                .put(a).put(b)
                .array();
    }
}