Re: RFID Credit Cards ...... are NOT safe.
if they where to implement a protocol such as SSL where RSA or El-Gamail is used to share keys i.e. asymetric key change followed by a what is considered to be a strong cipher like AES-256 I would feel fairly secure:
a) RSA is cracked, just to date impossible to commute. Against the laws of mathematics no magic happening in S-Box's.
b) Asymmetric key exchange with digital signatures has shown to be very secure. One easy, good example of secure cryptography.
Can that be implemented in a RFID card of today is another question. BTW AES-128 is not considered ver secure. minimum length by Rinajdel was always 256. NISA changed to 128 which was odd.