How to hash using SHA1(or similar cryptogrphical functions) a class(or struct) which has multiple keys, e.g.,

struct Foo{
   string name;
   int age;
   int score;
}

A naive approach is hash(has(name) hash(age) hash(score)), but hash collision is possible.

CodePudding user response：

Either hash the whole structure directly if it contains only POD (i.e. nothing allocated within and its sizeof is a constant): either you can use an union to get a proper byte array, or you use a cast to obtain a char* to provide to hash function.

If you have dynamic data inside your struct/class, you need to serialize all data and send them to the hash function - obviously, its size will vary during execution, because of dynamic data. But you must call hash only ONCE per data structure, and in NO WAY adding hashes together - that's a nonsense. You can also use a framework feature that will serialize your struct/class to a text stream (often XML or JSON format), and hash this serialization instead of the binary structure.

How to do all this is obviously platform-dependent - which cryptography API do you use, if you prefer.

By applying these principles, the collision (totally unavoidable, mathematically proven) won't be more than for any other kind of hashed data.