AES/CBC/NoPadding encryption and decryption

Question

I am using a microcontroller with NFC so I need to send encrypted data that why I am using AES/CBC/NoPadding while I am working on the android app I am having an issue with encryption and decryption this is the code I am working on

    String message="(*my_Log*y7VRMh5Wau80bRebLh/JaHMru/0Sj05E+lKUvT6d8Rw=*1604137444*19)111111111112";
    textView.setText("before encp:- "+message);
    try {
        String data=encrypt(message,"Thats my Kung Fu");
        Log.d("data after encode:-",data);
        textView.append("\n after encode:- \n"+data);
        String data2=decrypt(data,"Thats my Kung Fu");
        Log.d("data after decode:-",data2);
        textView.append("\n after decode:- \n"+data2);

    } catch (Exception e) {
        e.printStackTrace();
    }

}

@RequiresApi(api = Build.VERSION_CODES.O)
private String decrypt(String data, String key) throws Exception {
    SecretKeySpec skey = new SecretKeySpec(key.getBytes(), "AES");
    Cipher cipher=null;
    byte[] ivBytes = new byte[16];
    cipher = Cipher.getInstance("AES/CBC/PKCS7Padding");
    cipher.init(Cipher.DECRYPT_MODE,skey,new IvParameterSpec(ivBytes));
    byte[] decodeval=Base64.getDecoder().decode(data);
    byte[] decval= cipher.doFinal(decodeval);
    return new String(decval);

}

@RequiresApi(api = Build.VERSION_CODES.O)
private String encrypt(String message, String key) throws Exception{
    byte[] encval=null;
    SecretKeySpec skey = new SecretKeySpec(key.getBytes(), "AES");
    Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
    cipher.init(Cipher.ENCRYPT_MODE,skey);
    encval=cipher.doFinal(message.getBytes());
    String encryptedValue = Base64.getEncoder().encodeToString(encval);
    return encryptedValue;

}

and this is my log:- D/data after encode:-: zJSEw6H+abZFkwNA/pqpdZUMNFhY0KmZ2lXF23tdAVIm1C5L5oIMagWXG6NRt0UDcIy/xeAeHkEtf32+5WVQ420/TSljaxER7ynJ5+hgFMMo1qJHrWb8tZYUzMIvokUG

D/data after decode:-: �5ts��U0³u%Wau80bRebLh/JaHMru/0Sj05E+lKUvT6d8Rw=160413744419)111111111112

not complete decode also before encoding string size is 80 after encoding string size is 128 and after decade it's agin 80

Could you kindly share sample data that do work on NFC/microcontroler side (means you are trying to replicate the same encryption with Java/Android that takes place on NFC). As long as we don't know how the data is "regularly" encrypted we can't create code on another language that will work correctly. If your microcontroller has an API it would be perfect to share that link as well and hopefully there are examples (even if in other languages) that do work. Thanks — Michael Fehr, Nov 22 '20 at 13:23
my message is of length 80 and after encoding its size is 128 and no data for decode — Akhilesh Chaudhary, Nov 22 '20 at 13:31
kk now i added byte[] ivBytes = new byte[16]; cipher.init(Cipher.DECRYPT_MODE,skey,new IvParameterSpec(ivBytes)); — Akhilesh Chaudhary, Nov 22 '20 at 13:53
but output is D/data after decode:-: ��5��{GWau80bRebLh/JaHMru/0Sj05E+lKUvT6d8Rw=*1604137444*19)111111111112 — Akhilesh Chaudhary, Nov 22 '20 at 13:54
Are you trying to encrypt decrypt on Android to Android or Android to NFC? — kelalaka, Nov 22 '20 at 15:32
Then use already existing solutions. There is no need to reinvent. https://stackoverflow.com/a/22445878/1820553 — kelalaka, Nov 22 '20 at 17:40

score 0 · Accepted Answer · answered Nov 23 '20 at 04:42

@RequiresApi(api = Build.VERSION_CODES.O)
private String encrypt(String message, String key) throws Exception{
    byte[] encval=null;
    SecretKeySpec skey = new SecretKeySpec(key.getBytes(), "AES");
    Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
    byte[] ivBytes = new byte[16];
    cipher.init(Cipher.ENCRYPT_MODE,skey,new IvParameterSpec(ivBytes));   //iv here
    encval=cipher.doFinal(message.getBytes());
    String encryptedValue = Base64.getEncoder().encodeToString(encval);
    return encryptedValue;

}

you have to provide iv in encrypt too

AES/CBC/NoPadding encryption and decryption

1 Answers1