Encryption (AES)
I use AES algorithm for encrypt my data. When i encrypt 16 byte( one block) the result is 32 byte. I expect 16 byte but it generate 32 byte. If i use my code in string format the result is same. why?
My source code is
package chert.chert;
import chert.chert.R;
import chert.chert.SimpleCrypto;
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
public class ChertActivity extends Activity {
/** Called when the activity is first created. */
TextView textView1;
byte[] key=new byte[16];
byte[] state=new byte[16];
public SimpleCrypto Crypt = new SimpleCrypto(this);
@Override
public void onCreate(Bundle savedInstanceState) {
int i;
String ss,state_str,key_str;
char c;
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//=====================================================================================================================开发者_开发技巧=
state[0]=0x32; state[1]=(byte) 0x88; state[2]=0x31; state[3]=(byte) 0xe0;
state[4]=0x43; state[5]=0x5a; state[6]=0x31; state[7]=0x37;
state[8]=(byte) 0xf6; state[9]=0x30; state[10]=(byte) 0x98; state[11]=0x07;
state[12]=(byte) 0xa8; state[13]=(byte) 0x8d; state[14]=(byte) 0xa2; state[15]=0x34;
//======================================================================================================================
key[0]=0x2b; key[1]=0x28; key[2]=(byte) 0xab; key[3]=0x09;
key[4]=0x7e; key[5]=(byte) 0xae; key[6]=(byte) 0xf7; key[7]=(byte) 0xcf;
key[8]=0x15; key[9]=(byte) 0xd2; key[10]=0x15; key[11]=0x4f;
key[12]=0x16; key[13]=(byte) 0xa6; key[14]=(byte) 0x88; key[15]=0x3c;
//======================================================================================================================
try {
byte[] rawKey = Crypt.getRawKey(key);
byte[] result = Crypt.encrypt(rawKey, state);
} catch (Exception e) {
e.printStackTrace();
}
}
}
package chert.chert;
import java.security.SecureRandom;
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
public class SimpleCrypto {
public SimpleCrypto(ChertActivity chertActivity) {
// TODO Auto-generated constructor stub
}
public static String encrypt(String seed, String cleartext) throws Exception {
byte[] rawKey = getRawKey(seed.getBytes());
byte[] result = encrypt(rawKey, cleartext.getBytes());
return toHex(result);
}
public static String decrypt(String seed, String encrypted) throws Exception {
byte[] rawKey = getRawKey(seed.getBytes());
byte[] enc = toByte(encrypted);
byte[] result = decrypt(rawKey, enc);
return new String(result);
}
public static byte[] getRawKey(byte[] seed) throws Exception {
KeyGenerator kgen = KeyGenerator.getInstance("AES");
SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");
sr.setSeed(seed);
kgen.init(128, sr); // 192 and 256 bits may not be available
SecretKey skey = kgen.generateKey();
byte[] raw = skey.getEncoded();
return raw;
}
public static byte[] encrypt(byte[] raw, byte[] clear) throws Exception {
SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
Cipher cipher = Cipher.getInstance("AES");
cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
byte[] encrypted = cipher.doFinal(clear);
return encrypted;
}
private static byte[] decrypt(byte[] raw, byte[] encrypted) throws Exception {
SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
Cipher cipher = Cipher.getInstance("AES");
cipher.init(Cipher.DECRYPT_MODE, skeySpec);
byte[] decrypted = cipher.doFinal(encrypted);
return decrypted;
}
public static String toHex(String txt) {
return toHex(txt.getBytes());
}
public static String fromHex(String hex) {
return new String(toByte(hex));
}
public static byte[] toByte(String hexString) {
int len = hexString.length()/2;
byte[] result = new byte[len];
for (int i = 0; i < len; i++)
result[i] = Integer.valueOf(hexString.substring(2*i, 2*i+2), 16).byteValue();
return result;
}
public static String toHex(byte[] buf) {
if (buf == null)
return "";
StringBuffer result = new StringBuffer(2*buf.length);
for (int i = 0; i < buf.length; i++) {
appendHex(result, buf[i]);
}
return result.toString();
}
private final static String HEX = "0123456789ABCDEF";
private static void appendHex(StringBuffer sb, byte b) {
sb.append(HEX.charAt((b>>4)&0x0f)).append(HEX.charAt(b&0x0f));
}
}
If the length of the clear-text is a multiple of the block size, a whole new block is needed for padding according to PKCS#5. Say your clear-text is 16 bytes. The cipher-text will take 32 bytes.
It is something like the following
CipherTextLength = (PlainTextLength / 16 + 1) * 16;
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