MiFARE Classic Authentication works
While working on librfid support for the Pegoda Reader (which is basically 50% done now), I've discovered what my problem with librfid's MiFARE classic support was: I was using the wrong keys. Apparently Transponders issued by Philips have { 0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5 } as their default key, whereas Transponders from Infineon have { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff }.
I seem to have Infineon samples, and I always tried with the Philips key. After fixing this, reading sectors off a MiFARE classic card seems to be working.