Why Does Converting a Byte Array to a String and Back Result in Data Loss During Decryption?

Difficulties in Byte Array Conversion to String and Reconversion

Question:

Why does the byte array obtained after converting a string back from a byte array differ from the original byte array, causing decryption errors?

Solution:

Encoding encrypted data as strings can be problematic due to the nature of string encodings. For binary data, using byte arrays is recommended. However, if string storage is necessary, one must select an encoding with a one-to-one mapping between bytes and characters, such as ISO-8859-1. Using encodings like UTF-16 can result in data loss due to added byte-order markers and the potential for ambiguous character mappings.

Consider the following example:

String decoded = new String(encryptedByteArray, "ISO-8859-1");
byte[] encoded = decoded.getBytes("ISO-8859-1");

Using ISO-8859-1 preserves the original byte array, ensuring correct decryption.

UTF-16 fails due to:

• Adding a byte-order-marker when encoding, which must be ignored while decoding.
• The potential for character mappings where multiple bytes map to a single character, losing information.

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