This commit fixes issue #91.
[AN10922][] specifies the key diversification algorithms used by the
MIFARE SAM AV3. Support for these algorithms was added to
`libfreefare` via pull-request #79.
However, while every attempt was made to write a faithful
implementation, the implemented code did not properly handle cases
where the diversification data was less than or equal to the block
size of the cipher: 16 bytes for AES, and 8 bytes for DES. This
bug was identified in issue #91.
This commit addresses this problem while providing a way to revert to
the previous behavior in cases where it is necessary to maintain
previous deployments. This was accomplished by introducing a new
`flags` parameter to the `mifare_key_deriver_new_an10922` method.
Normally, `flags` should simply be set to `AN10922_FLAG_DEFAULT`.
However, if the previous behavior is required, it should be set to
`AN10922_FLAG_EMULATE_ISSUE_91`.
[AN10922][] does not include any test vectors that might have helped to
identify this problem earlier. However, [AN10957][] (pages 13-14) was
found to have a suitable example usage of [AN10922][] with an
appropriately short value for *M* that we are using as a test vector
to verify correct behavior.
Note that the issue being addressed here is not a security issue:
using the `AN10922_FLAG_EMULATE_ISSUE_91` should not be any less
secure than using `AN10922_FLAG_DEFAULT`.
[AN10922]: https://www.nxp.com/docs/en/application-note/AN10922.pdf
[AN10957]: https://www.nxp.com/docs/en/application-note/AN10957.pdf
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