Why are My Decrypted AES/CBC Strings in Java Showing Incorrect Initial Bytes?

Incorrect Initial Bytes in Java AES/CBC Decryption

When using AES/CBC encryption in Java, erroneous initial bytes may appear in the decrypted string. This issue arises due to inadequate encryption parameters.

To decipher the problem, ensure that the following steps are implemented:

1. Proper Initialization of Cipher: Initialize the encryption cipher with both the secret key and an initialization vector (IV):

Cipher encryptCipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
encryptCipher.init(Cipher.ENCRYPT_MODE, aesKey, ivParameterSpec);

2. Initialization Vector (IV): Include the IV in the cipher initialization to guarantee different ciphertexts even with identical inputs and keys.
3. Proper Initialization of InputStream: Initialize the input stream for decryption with the cipher, not the encrypted bytes:

CipherInputStream cipherInputStream = new CipherInputStream(inStream, decryptCipher);

By adhering to these steps, the initial bytes in the decrypted string should now be correct, resulting in accurate information extraction.

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