Cryptographic Checksum

Cryptographic checksum is a value (shortly, checksum) that formed mathematically and assigned to a file to validate the file against modification or interference and to verify that the data contained in the file has not been maliciously or mistakenly changed. Cryptographic checksums are used in data transmission and data storage.

They can be created by performing a complicated series of cryptographic algorithm (which is a mathematical operation) that converts the data into a fixed string of digits called a hash value. This string of values should be unique when any other dissimilar value hashed by same method of encryption. Consequently, no other string should be able to generate the same value. In fact, without knowing the knowledge of cryptography algorithm which has used to create the hash value, it should be impossible to decipher the hashed value to the original value of text.

The ideal cryptographic hash function has four main properties:

• it is easy to compute the hash value for any given message
• it is infeasible to generate a message from its hash
• it is infeasible to modify a message without changing the hash
• it is infeasible to find two different messages with the same hash.

Degree of Difficulty

In cryptographic practice, “difficult” generally means “almost certainly beyond the reach of any adversary who must be prevented from breaking the system for as long as the security of the system is deemed important”. The meaning of the term is therefore somewhat dependent on the application, since the effort that a malicious agent may put into the task is usually proportional to his expected gain. However, since the needed effort usually grows very quickly with the digest length, even a thousand-fold advantage in processing power can be neutralized by adding a few dozen bits to the latter.