IllegalBlockSizeException when trying to encrypt and decrypt a string using AES

Question

I have a hard key with which I want to encrypt a string before saving it to SharedPreferences . This is the code that I still have:

 public class TokenEncryptor { private final static String TOKEN_KEY = "91a29fa7w46d8x41"; public static String encrypt(String plain) { try { Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding"); AlgorithmParameterSpec ivSpec = new IvParameterSpec(new byte[16]); SecretKeySpec newKey = new SecretKeySpec(TOKEN_KEY.getBytes(), "AES"); cipher.init(Cipher.ENCRYPT_MODE, newKey, ivSpec); return new String(cipher.doFinal(plain.getBytes())); } catch (Exception e) { Ln.e(e); return null; } } public static String decrypt(String encoded) { try { Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding"); AlgorithmParameterSpec ivSpec = new IvParameterSpec(new byte[16]); SecretKeySpec newKey = new SecretKeySpec(TOKEN_KEY.getBytes(), "AES"); cipher.init(Cipher.DECRYPT_MODE, newKey, ivSpec); return new String(cipher.doFinal(encoded.getBytes())); } catch (Exception e) { Ln.e(e); return null; } } } 

There seems to be an exception at the end of the decrypt method as an exception:

javax.crypto.IllegalBlockSizeException: error:0606506D:digital envelope routines:EVP_DecryptFinal_ex:wrong final block length

Can someone point me in the right direction? I have a feeling that I'm doing something wrong creation IvParameterSpec .

Answer 1

When you encrypt a string with AES, you return an array of bytes. Trying to convert these bytes directly to a string ( new String(cipher.doFinal(plaintextBytes)) ) will cause all kinds of problems. If you need output from your encryption method as a string, use Base64 instead of trying a direct conversion. In your decryption method, convert the Base64 string back to a byte array before decrypting the byte array.

Also, do not use getBytes() , since the output depends on the system defaults. Use getBytes("utf-8") or whatever. This removes the ambiguity.

Answer 2

Just in case someone is interested (or feels too lazy to do their research), here is the result code for AES-256 encryption and decryption, which I put together using the accepted answer and comments:

 public class TokenEncryptor { private final static String TOKEN_KEY = "fqJfdzGDvfwbedsKSUGty3VZ9taXxMVw"; public static String encrypt(String plain) { try { byte[] iv = new byte[16]; new SecureRandom().nextBytes(iv); Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding"); cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(TOKEN_KEY.getBytes("utf-8"), "AES"), new IvParameterSpec(iv)); byte[] cipherText = cipher.doFinal(plain.getBytes("utf-8")); byte[] ivAndCipherText = getCombinedArray(iv, cipherText); return Base64.encodeToString(ivAndCipherText, Base64.NO_WRAP); } catch (Exception e) { Ln.e(e); return null; } } public static String decrypt(String encoded) { try { byte[] ivAndCipherText = Base64.decode(encoded, Base64.NO_WRAP); byte[] iv = Arrays.copyOfRange(ivAndCipherText, 0, 16); byte[] cipherText = Arrays.copyOfRange(ivAndCipherText, 16, ivAndCipherText.length); Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding"); cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(TOKEN_KEY.getBytes("utf-8"), "AES"), new IvParameterSpec(iv)); return new String(cipher.doFinal(cipherText), "utf-8"); } catch (Exception e) { Ln.e(e); return null; } } private static byte[] getCombinedArray(byte[] one, byte[] two) { byte[] combined = new byte[one.length + two.length]; for (int i = 0; i < combined.length; ++i) { combined[i] = i < one.length ? one[i] : two[i - one.length]; } return combined; } } 

Answer 3

This extension of Artjom B answers and works for me.

 public String encryptMsg(String message, SecretKey secret) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, InvalidParameterSpecException, IllegalBlockSizeException, BadPaddingException, UnsupportedEncodingException { Cipher cipher = null; cipher = Cipher.getInstance("AES/ECB/PKCS5Padding"); cipher.init(Cipher.ENCRYPT_MODE, secret); byte[] cipherText = cipher.doFinal(message.getBytes("UTF-8")); return Base64.encodeToString(cipherText, Base64.NO_WRAP); } public String decryptMsg(String cipherText, SecretKey secret) throws NoSuchPaddingException, NoSuchAlgorithmException, InvalidParameterSpecException, InvalidAlgorithmParameterException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException, UnsupportedEncodingException { Cipher cipher = null; cipher = Cipher.getInstance("AES/ECB/PKCS5Padding"); cipher.init(Cipher.DECRYPT_MODE, secret); byte[] decode = Base64.decode(cipherText, Base64.NO_WRAP); String decryptString = new String(cipher.doFinal(decode), "UTF-8"); return decryptString; }