mifare_ultralightc_authenticate function isn't working as expected

[bluetiger30]

Hi , Thanks for this great library.

so I changed the 1st byte of the key from 0x49 to 0x48 in the mifare-ultralight-info which should tell me that authentication has failed because its not the correct key, however, it returns success !!!

if i change 0x49 to x40 it returns fail, so I'm not sure what is happening with the authenticate function

any idea on why it doesn't always provide the correct result?

[graynk]

It will always return success after auth, but the following commands will yield error if the key was wrong, so you won't be able to read anything. I believe this is the problem of the card itself, not the library. You could check error status two times to circumvent the issue.

[darconeous]

The least-significant bits of the 128-bit representation of the 2K3DES key are unused by the MIFARE Ultralight C.

Remember that DES uses 56-bit keys, but convention is to give the key in 64-bits—using the least significant bits of each byte as a parity check bit. The MIFARE Ultralight C ignores the parity bits.

This is why changing 0x49 to 0x48 doesn't cause the authentication to fail, but 0x49 to 0x40 does: in the former case you aren't actually changing any bits of the key, you are just changing the (unused) parity bit from 1 to 0. In the later case you are actually changing the bits of the key and the authentication handshake fails accordingly.

[darconeous]

Bottom line: mifare_ultralightc_authenticate behaved correctly in both cases.