Mifare Ultralight: lock specific pages

Question

I got reference from this link (Mifare Ultralight C Lock) to make all pages on a Mifare Ultralight tag read-only.

I can write a message on a Mifare Ultralight tag successfully on Android. Now I want to lock pages 4 to 7 (or any specific page). The above link only shows how to lock all pages. How I can lock specific pages?

This code locks all pages:

mifare.transceive(new byte[] {
    (byte)0xA2,  /* CMD = WRITE */
    (byte)0x02,  /* PAGE = 2    */
    (byte)0x00, (byte)0x00, (byte)0xFF, (byte)0xFF  /* DATA = lock pages 3..15*/
});

public static boolean writeOnMifareUltralight(Context _context, Tag tag,String pageData, int i) {
    byte[]result;
    MifareUltralight mifare = null;
    try {

        mifare = MifareUltralight.get(tag);
        mifare.connect();
        mifare.writePage(i, pageData.getBytes(Charset.forName("US-ASCII")));

        mifare.transceive(new byte[] {
            (byte)0xA2,  /* CMD = WRITE */
            (byte)0x02,  /* PAGE = 2    */
            (byte)0x00, (byte)0x00, (byte)0xFF, (byte)0xFF/* DATA = lock pages 3..15*/
        });
    } catch (Exception ex) {
        ex.printStackTrace();
        Log.d("mtw", ex.getMessage());
        // return false;
    } finally {
        try {
            mifare.close();
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
    return true;
}

Rescript

Sorry, where did you found the package for MifareUltralight? Thanks. – Chose

Answer 1

The lock bytes of MIFARE Ultralight use one bit to lock one block. In addition they contain 3 block locking bits that control the lock status of the lock bytes themselves.

• Byte 2 (on page 2): Bits 3-7 are the lock bits for pages 3-7. Thus, bit 3 locks page 3, bit 4 locks page 4, etc. The lower three bits are the block locking bits. Bit 0 locks the lock bit for page 3, bit 1 locks the lock bits for pages 4-9, and bit 2 locks the lock bits for pages 10-15.

• Byte 3 (on page 2): Bits 0-7 are the lock bits for pages 8-15. Thus, bit 0 locks page 8, bit 1 locks page 9, etc.

So, for example, to lock pages 4-7, you could use the following command:

mifare.transceive(new byte[] {
    (byte)0xA2,  /* CMD = WRITE */
    (byte)0x02,  /* PAGE = 2    */
    (byte)0x00, (byte)0x00, (byte)0xF0, (byte)0x00 /* DATA = lock pages 4..7*/
});

Note that instead of mifare.transceive() you could also simply use mifare.writePage():

mifare.writePage(2, new byte[] {
    (byte)0x00, (byte)0x00, (byte)0xF0, (byte)0x00 /* DATA = lock pages 4..7*/
});

Keep in mind that lock bits are one-time-programmable. Hence, once a lock bit is set to logical 1 (i.e. LOCKED), it can't be reversed to a logical 0 (i.e. UNLOCKED).

This also allows you to set one lock bit at a time. For instance, to set page i LOCKED (where 3 <= i <= 15 !!!), something like this should work:

mifare.transceive(new byte[] {
    (byte)0xA2,  /* CMD = WRITE */
    (byte)0x02,  /* PAGE = 2    */
    (byte)0x00, (byte)0x00, (byte)((1<<i) & 0x0FF), (byte)(((1<<i)>>>8) & 0x0FF)
});

Ambassador

thanks this is can write page4 only and can't write 5 to 7 but lock page 4 to 7.. – Rescript

I'm mean before write with lock i call that answer can update write page 4 only can't write page 5 to 7. I want page 4 to 7 update write with lock page(write only one time). – Rescript

@loveme If you want to lock only one of the pages, then only set the lock bit for that one page to '1'. The lock bits are accumulated (logical OR) with each update of the lock bits page. – Ambassador

Thanks sir, I can do that I'm wrong I mean after i write 4 to 7 page I just locking for that page I got condition mifare.connect(); mifare.writePage(i, pageData.getBytes(Charset.forName("US-ASCII"))); if(i==7){ your code }. – Rescript

If you write all pages at the same time, then this would probably be the preferable way. If you only write one page, each time the tag is tapped, then you might want to only lock that specific page. See my updated answer... – Ambassador

Sir, Michael Roland.It is possible second time want to lock page 8 to 11. – Rescript

Thanks you so much sir ,I can try all of them.I'm suitable understand about lock memory MIFARE Ultralight NFC .thanks for help me .. ...good luck for you – Rescript