about SHA-1 and the search engine

Why this website exist

The secure hash algorithm 1 (SHA-1) is a one-way hash function. One-way functions like MD5 or SHA1-1 are very important at the public key cryptography, because they are relatively easy to compute but much harder to reverse. That means if you have a function f(x) you can easy compute the result of it, but not (in most cases) the input "x" from the result. That makes clear why it is called "one-way" function.

The cryptographer Bruce Schneier use this example in his Book "Applied Cryptography": "Breaking a plate is a good example of a one-way function. It is easy to smash a plate into a thousands tiny pieces. However, it's not easy to put all of those tiny pieces back together into a plate.". Hash functions are built to be collision-free and to make it very hard, imposible in most cases, to generate two pre-images with the same hash value. SHA-1 is "secure" and current the state of the art, so it is used in most cases.

As you see, we can't use a hash function for encryption and decryption. Hashes are often used to save the integrity of a file. E.g. if you download a file from the internet and hash the file on your computer. If the website where you downloaded the file publish a hash of it, you compare them. If the hash is not eqal, the file is corrupted.

But we are interested in short words like passwords or hashed timestamps. In practice they are used e.g. in bulletin boards to save the password from the user into the database. But the bulletin board doesn't save the cleartext, just the hash of it. So if you make a login, it compares your hash with the hash in the database.

About the search engine

The target of this website is to make a big hash table. You can search for a word and you can search for a SHA-1 hash. That is good if you forget your password or other bits you hash. It saves your input if it is not in the database, so it grow with each unknown search. Of course you can never put all hashes into the database, but some of it. That one, you search for. So we have a search engine with human intelligence. That makes it small, fast and nice to have.

It searches for strings if you type less than 30 letters, if you search for >30 letters it looks for the SHA-1 hash. Again: All inputs will be saved if they are not in the database. Please keep that in mind!