Users have been known to share their passwords. Statistical attack on the encrypted data. Statistical attack is the real proof of an encryption method's security. A statistical method does not attempt to try every locking combination but instead attempts to determine the pattern of bit changes needed to reduce the randomness of the file. Poor encryption methods such as XOR masks can be decrypted rapidly with these methods.
More sophisticated methods require more time.
Although mathematicians can make intelligent guesses about the relative security of different encryption methods, the real proof is in the test of time. If many mathematicians working over many years cannot do better than trying every combination then the encryption algorithm is considered secure. A number of excellent algorithms have been developed that have passed successive testing by many people. It is extremely fast due to its taking advantage of built-in instructions on the current microprocessors for the basic bit shuffling operations. It was placed in the public domain and can be distributed without limitation.