libtasn1 relaxig asn1_der_decoding() size test

[Karel Slany]

Hello,

I've run into a problem with asn1_der_decoding() recently. I have to
decode some DER data which I'm obtaining from a third party source. The
problem is that most of the time the obtained DER data contain some
additional trailing bytes.

The function
asn1_der_decoding (asn1_node * element, const void *ider, int ider_len,
                   char *errorDescription)
, as it is implemented now, expects @ider to have the exact length of
@ider_len. But in my case, @ider_len is slightly larger because of the
aforementioned padding. This causes the whole function to end with
ASN1_DER_ERROR even though the supplied DER was properly parsed.

A solution to my this problem may be:
* relaxing the test at the end of the function (example in the supplied
patch)
* introducing a new function witch such properties (this function could
also give a hint about the real DER size)
* adding a flag to asn1_der_decoding() whether the function should
perform a strict size test (this would break backward compatibility)

My personal favourite is the second choice. Please let me know whether
you are willing to accept any of these changes/enhancements. If so, I
could send you a patch with the changes.

Best regards,
Karel.

relax_decoding_test.diff
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