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Up to overview | Next: Data integrity
A one-way hash function takes a variable-length input and converts it to a fixed-length binary sequence (hash value).
The reverse process to a good one-way hash function, finding a string that corresponds to a given hash value, is difficult. Another important feature is that finding two different input strings, generating the same hash value, is hard.
These properties mean that even a minimal change in the input string should render the corresponding hash value unrecognizable, when compared to the previous value. As a result, one-way hash functions are commonly employed for data integrity, but also for secure storage of passwords.
One well-known one-way hash function is the MD5-Message Digest Algorithm, producing 128-bit hash values. It was designed by Ron Rivest and it's described in RFC 1321. An implementation of the MD5 algorithm is included in the appendix of RFC 1321.