We are familiar with parity and CRC. Neither of these checks has the ability to resist data tampering. They can detect and correct channel errors in data transmission to a certain extent, but they cannot prevent malicious destruction of data.

The "digital fingerprint" feature of md5 hash algorithm makes it the most widely used file integrity checksum algorithm at present, and many Unix systems provide commands to calculate MD5 checksum.

2) Digital signature

Hash algorithm is also an important part of modern cryptography. Because of the slow operation speed of asymmetric algorithm, one-way hash function plays an important role in digital signature protocol. The digital signature of hash value, also known as "digital digest", can be regarded as equivalent to the digital signature of the file itself statistically. In addition, the protocol has other advantages.