No matter what algorithm is used, it is always possible to decrypt data by trying all possible keys. The only problem is the time this would take. The longer the key, the more secure is the encrypted data. To illustrate, trying possible values of a 128-bit key would take several thousand trillion years. With development and growth of computer power, the time required to try all values of a 128-bit key will decrease, however in the near future a 128-bit key will be enough to provide reliable and secure data encryption.
Trying an asymmetric key is an even more difficult task, since asymmetric keys are much longer than symmetric keys. Guessing such a key will take even greater amounts of time, since this method involves a factorial expansion of a big number. Nowadays, there are no effective algorithms which would allow you to perform such calculations in a reasonable amount of time. Thus, public key cryptography is considered to be secure.