Key Length and Encryption Strength
The strength of encryption is related to the difficulty of discovering the key, which in turn depends on both the cipher used and the length of the key.
Encryption strength is often described in terms of the size of the keys used to perform the encryption. Generally, a longer key will provide a stronger encryption. Key length is measured in bits. For example a 128-bit key would be stronger than a 40-bit key.
However, because of the math associated with their algorithms; some ciphers can use only a subset of the possible values for a given key length, while other ciphers can use all possible values for a given key length. Therefore, different ciphers may require different key lengths to achieve the same level of encryption strength.
Here are some links to learn more about Hashing Algorithms, Symmetric Keys, and Asymmetric Keys.