Bruteforce: sounds like a force?¶
What would you do if you are given a 4-digit padlock which opens only when the entered 4 digits are right. The basic approach to break this lock would be to guess different combinations of digits so as to get the right sequence which opens the lock.
This way of guessing or trying out all possible ways to break an encryption is called bruteforce.
Key length, as the name says, is the length of the key whereas key space is the possible keys available for encryption. Message space is the number of possible values that a plain text might be encrypted as.
If the key length and the key space of an encryption system is limited then it becomes very easy for the attacker to try out different possible keys ( as there are only a limited number to try out ) and carry out a bruteforce attack easily. Also, if the message space is limited it becomes easy for the attacker to easily guess which plain text was encrypted.