CODEWITHSUNDEEP
androidaes
Hitesh Dhamshaniya
Hitesh Dhamshaniya

Reputation: 2182

How to remove PKCS7 padding from an AES encrypted string in android?

I'm working on a security application using my own customized cryptography method, and having a problem on message decryption.

Here is an my Code

private static void myCryptography(){

Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
byte[] input = "Hitesh Dhamshaniya".getBytes();
byte[] keyBytes = "ABCD657865BHNKKK".getBytes();
SecretKeySpec key = new SecretKeySpec(keyBytes, "AES");
Cipher cipher = Cipher.getInstance("AES/ECB/PKCS7Padding", "BC");

// encryption pass

cipher.init(Cipher.ENCRYPT_MODE, key);
byte[] cipherText = new byte[cipher.getOutputSize(input.length)];
int ctLength = cipher.update(input, 0, input.length, cipherText, 0);
ctLength += cipher.doFinal(cipherText, ctLength);
Log.e("==> ", " == > Encode " + Base64.encodeToString(cipherText, Base64.DEFAULT));
String encodedStr = Base64.encodeToString(cipherText, Base64.DEFAULT);
// decryption pass

cipherText = Base64.decode(encodedStr, Base64.DEFAULT);
cipher.init(Cipher.DECRYPT_MODE, key);
byte[] plainText = new byte[cipher.getOutputSize(ctLength)];
int ptLength = cipher.update(cipherText, 0, ctLength, plainText, 0);
ptLength += cipher.doFinal(plainText, ptLength);
Log.e("==> ", " == > Decoded " + new String(plainText, "UTF-8"));

}

Getting below output

== > Encode TteNmufoa5AWWmEPBmQ3N8fdqRpahvwUR7CSclAcsjM=

== > Decoded Hitesh Dhamshaniya���������������������

How to remove unwanted character like '��' from decode string.

Upvotes: 3

Views: 1606

Answers (1)

Henry
Henry

Reputation: 43788

The cipher removes the padding automatically. What you see here comes from the conversion of the byte array plainText to the string. You should only use the first ptLength bytes instead of the whole array:

new String(plainText, 0, ptLength, "UTF-8")

Upvotes: 3

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