Java AES-128 ECB encryption

Question

I have received a message from AT5 (Atrack) unite encoded with AES-128 ECB encryption and this is the key in hex (33333838000000000000000000000000) the original key is in string "3388" and this is the cipher that i received but i convert it to hex

Whenever I try to decrypt the message, I face this exception:

Error while decrypting: javax.crypto.IllegalBlockSizeException: Input length must be multiple of 16 when decrypting with padded cipher

Here is my code:

    orginalString 

 ?U??????}MgD?R???`????
#?j????g:N???@???$=???r?u?>~??Qh,?N?????3?8:?-E??;?b<J??I?v{?'o?m[?|?CY?n????K????>?ã??<?,????  ??f?'???}&?}?7r%??93??!u?0D?3Ig|??%'????*??`?Y^?M?4J?I?>?tIu???;?RR;2??{nrl??us
?R?F?oi????



String strToDecrypt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
secretKey = new SecretKeySpec("33333838000000000000000000000000".getBytes("UTF-8"), "AES");

Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5PADDING");
cipher.init(Cipher.DECRYPT_MODE, secretKey);
byte[] cipherResult = cipher.doFinal(Base64.decodeBase64(strToDecrypt));

share the code of how strToDecrypt is generated. Base64.decodeBase64(strToDecrypt) would result in a byte array of size 900. 900 has 4 remaining when divided by 16. — kamyar haqqani
it's being generated from hardware device we only control the key which is "3388" — Mostafa Hafez

Ebbe M. Pedersen Ebbe M. Pedersen · Accepted Answer · 2018-11-15T15:46:35

Your strToDecrypt seems to be hex encoded, not base64 encoded .. so you need to hex decode it before decrypting, instead of base64 decoding. But actually you encrypted data if hex decoded, would also end up having an invalid size. Your hex string is 1200 hex chars = 600 bytes = 37.5 AES blocks of 16 bytes .. Something seems to be wrong with your data ..

Also, your key is also Hex encoded, so you need to hex decode it .. not just do a getBytes(..).

Java AES-128 ECB encryption

1 Answers