A Brute-Force attack, also known as exhaustive key search, is a hack using complex algorithms attempting to crack a password or key by trial and error to find the correct plaintext or password. As the password’s length increases, the amount of time needed to find the correct password increases exponentially.
Brute-Force Attacks are often made less effective by the use of obfuscating or complicating the data to be encoded. This makes it harder for an attacker to recognize when they’ve cracked the key, in turn making it more work and extending the computational power needed.
The amount of time needed to crack the key depends on the size of the key. The theorized time it will take for any algorithm to crack the key is used as a metric to test the strength of the system, a larger key system in turn exponentially increases the resources required for an attack. The maximum number of attempts to crack the key is equal to 2^key size, key size representing bits.
As bigger key sizes mean better security, cryptographic keys have increased in size. Currently, most cryptographic algorithms like Bitcoin use SHA-256 as it is a system using 256 bit-keys.