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Home/ Questions/Q 8683583
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Editorial Team
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Editorial Team
Asked: June 12, 20262026-06-12T22:05:04+00:00 2026-06-12T22:05:04+00:00

In my little NFC related project i’m trying to set a byte[] as authentication

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In my little NFC related project i’m trying to set a byte[] as authentication key for the Mifare Classic 1k chips i’m using. When is set it like this:

private byte[] key = {(byte)0xff, (byte)0xff, (byte)0xff, (byte)0xff, (byte)0xff, (byte)0xff};

it ends up being -1 -1 -1 -1 -1 -1… Why is Android translating it like this, and, how should it really be coded?

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  1. Editorial Team
    Editorial Team
    2026-06-12T22:05:05+00:00Added an answer on June 12, 2026 at 10:05 pm

    This has nothing to do with Android or NFC, this is is how Java works. byte‘s are signed, which means that one of the bits is used as the sign. 0xff=11111111, which happens to mean -1 for Java. Your MIFARE card doesn’t care about this though, so your program should work fine.

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