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Editorial Team
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Asked: 2026-05-28T17:15:26+00:00

I have a file encrypted with java application using AES. I also have a

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I have a file encrypted with java application using AES. I also have a key file was encrypted with. But i can’t understand how to use the key to decrypt file. Most tutorials and examples create temporary random key, encrypt file and decrypt it in one place.
So, question is how to specify a key which have to be used for decryption?

EDIT:
Samples i found use following code to generate key. I have no idea where i can use my key here.

KeyGenerator kgen = KeyGenerator.getInstance("AES");
kgen.init(128);
SecretKey key = kgen.generateKey();
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1 Answer

  1. Editorial Team

    Just to summarise my comments to Lucifer’s answer.

    1. If you don’t know what padding was used to encrypt, then decrypt with ‘no padding’ set. That will decrypt everything, including the padding, and won’t throw an error because of mismatched padding.

    2. When you have decrypted the cyphertext, have a look at the last block of the output and see what padding was used. Different paddings leave different byte patterns, so it is usually easy enough to tell.

    3. Set your decryption method to expect the correct type of padding, and it will be automatically removed for you.

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