The full name of the AES algorithm is Advanced Encryption Standard. It is a typical "symmetric encryption algorithm" whose main function is to ensure that private information is not leaked.
1. Key
The key is the basis for the encryption and decryption of the AES algorithm, because it requires the use of the same key for encryption and decryption of plaintext .
AES supports three key lengths: 128 bits, 192 bits, and 256 bits.
2. Filling
When the AES algorithm encrypts plaintext, it does not encrypt the entire plaintext into a piece of ciphertext, but splits the plaintext into an independent plaintext block. Each plaintext block is 128 bits long, which means that each plaintext block is 16 bits in length. Bytes (8 bits per byte).
Fill mode:
1. NoPadding: No padding is performed, but the plaintext must be an integer multiple of 16 bytes.
2. PKCS5Padding (default): If the plaintext block is less than 16 bytes (128bit), the corresponding number of characters is added to the end of the plaintext block, and the value of each byte is equal to the missing number of characters.
For example, plaintext: {1,a,3,c,5,k,6,8,l,o}, if 6 bytes are missing, the complement is {1,a,3,c,5,k,6,8 ,l,o, 6,6,6,6,6,6 }
3. ISO10126Padding: If the plaintext block is less than 16 bytes, the corresponding number of bytes is added to the end of the plaintext block. The last character value is equal to the missing number of words, and the other characters are filled with random numbers.
For example, plaintext: {1,a,3,c,5,k,6,8,l,o}, if 6 bytes are missing, it may be supplemented as {1,a,3,c,5,k,6, 8,l,o, 2,i,9,q,7,6 }.
3. Mode
The AES encryption algorithm provides different working modes:
1. ECB mode (default): Electronic Codebook Book mode
2. CBC mode: Cipher Block Chaining mode (Cipher Block Chaining)
3. CTR mode: Calculator mode (Counter)
4. CFB mode: Cipher FeedBack mode (Cipher FeedBack)
5. OFB mode: Output FeedBack mode (Output FeedBack)
4. AES-CBC mode encryption and decryption
1. aes_activity.xml layout:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".AesActivity">
<EditText
android:id="@+id/etData"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<Button
android:id="@+id/aesEncryption"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="AES加密" />
<TextView
android:id="@+id/tvEncryption"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="5dp"
android:gravity="center" />
<Button
android:id="@+id/aesDecrypt"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="AES解密" />
<TextView
android:id="@+id/tvDecrypt"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="5dp"
android:gravity="center" />
</LinearLayout>2. Encryption and decryption code:
Create an AesUtils class:
public class AesUtils {
private static final String SHA1PRNG = "SHA1PRNG"; // SHA1PRNG 强随机种子算法
private static final String AES = "AES"; //AES 加密
private static final String CIPHERMODE = "AES/CBC/PKCS5Padding"; //AES算法/CBC模式/PKCS5Padding填充模式
/**
* 加密
*/
public static String encrypt(String key, String cleartext) {
if (TextUtils.isEmpty(cleartext)) {
return cleartext;
}
try {
byte[] result = encrypt(key, cleartext.getBytes());
return parseByte2HexStr(result);
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
/**
* 加密
*/
public static byte[] encrypt(String key, byte[] clear) throws Exception {
byte[] raw = getRawKey(key.getBytes());
SecretKeySpec skeySpec = new SecretKeySpec(raw, AES);
Cipher cipher = Cipher.getInstance(CIPHERMODE);
cipher.init(Cipher.ENCRYPT_MODE, skeySpec, new IvParameterSpec(new
byte[cipher.getBlockSize()]));
byte[] encrypted = cipher.doFinal(clear);
return encrypted;
}
/**
* 解密
*/
public static String decrypt(String key, String encrypted) {
if (TextUtils.isEmpty(encrypted)) {
return encrypted;
}
try {
byte[] enc = parseHexStr2Byte(encrypted);
byte[] result = decrypt(key, enc);
return new String(result);
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
/**
* 解密
*/
public static byte[] decrypt(String key, byte[] encrypted) throws Exception {
byte[] raw = getRawKey(key.getBytes());
SecretKeySpec skeySpec = new SecretKeySpec(raw, AES);
Cipher cipher = Cipher.getInstance(CIPHERMODE);
cipher.init(Cipher.DECRYPT_MODE, skeySpec, new IvParameterSpec(new
byte[cipher.getBlockSize()]));
byte[] decrypted = cipher.doFinal(encrypted);
return decrypted;
}
/**
* 处理密钥
*/
@SuppressLint("DeletedProvider")
public static byte[] getRawKey(byte[] seed) throws Exception {
KeyGenerator kgen = KeyGenerator.getInstance(AES);
//for android
SecureRandom sr = null;
// 在4.2以上版本中，SecureRandom获取方式发生了改变
if (android.os.Build.VERSION.SDK_INT >= 17) {
sr = SecureRandom.getInstance(SHA1PRNG, new CryptoProvider());
} else {
sr = SecureRandom.getInstance(SHA1PRNG);
}
sr.setSeed(seed);
kgen.init(128, sr); //128bits,192bits,256bits
//AES中128位密钥，加密轮次为10轮；192位密钥，加密轮次为12轮；256位密钥，加密轮次为14轮。
SecretKey skey = kgen.generateKey();
byte[] raw = skey.getEncoded();
return raw;
}
/**
* 将二进制转换成16进制
*/
public static String parseByte2HexStr(byte buf[]) {
StringBuilder sb = new StringBuilder();
for (int i = 0; i < buf.length; i++) {
String hex = Integer.toHexString(buf[i] & 0xFF);
if (hex.length() == 1) {
hex = '0' + hex;
}
sb.append(hex.toUpperCase());
}
return sb.toString();
}
/**
* 将16进制转换为二进制
*/
public static byte[] parseHexStr2Byte(String hexStr) {
if (hexStr.length() < 1)
return null;
byte[] result = new byte[hexStr.length() / 2];
for (int i = 0; i < hexStr.length() / 2; i++) {
int high = Integer.parseInt(hexStr.substring(i * 2, i * 2 + 1), 16);
int low = Integer.parseInt(hexStr.substring(i * 2 + 1, i * 2 + 2),
16);
result[i] = (byte) (high * 16 + low);
}
return result;
}
public static class CryptoProvider extends Provider {
public CryptoProvider() {
super("Crypto", 1.0, "HARMONY(SHA1 digest;SecureRandom;SHA1withDSA signature)");
put("SecureRandom.SHA1PRNG", "org.apache.harmony.security.provider.crypto.SHA1PRNG_SecureRandomImpl");
put("SecureRandom.SHA1PRNG ImplementedIn", "Software");
}
}
}3. AesActivity code:
package com.example.myapplication;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class AesActivity extends AppCompatActivity implements View.OnClickListener {
//AES加密
private Button aesEncryption;
private TextView tvEncryption;
//AES解密
private Button aesDecrypt;
private TextView tvDecrypt;
//输入框
private EditText etData;
//加密解密的key
String key = "1234567890";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_aes);
initView();
}
private void initView() {
aesEncryption = findViewById(R.id.aesEncryption);
aesDecrypt = findViewById(R.id.aesDecrypt);
tvEncryption = findViewById(R.id.tvEncryption);
tvDecrypt = findViewById(R.id.tvDecrypt);
etData = findViewById(R.id.etData);
aesEncryption.setOnClickListener(this);
aesDecrypt.setOnClickListener(this);
}
@Override
public void onClick(View v) {
//要加密的字符串
String encryptData = etData.getText().toString();
switch (v.getId()) {
case R.id.aesEncryption://加密
tvEncryption.setText(AesUtils.encrypt(key, encryptData));
break;
case R.id.aesDecrypt://解密
tvDecrypt.setText(AesUtils.decrypt(key, tvEncryption.getText().toString()));
break;
default:
break;
}
}
}5. Result chart
