Shamir's Secret Sharing

This tool is a practical realization of Shamir's secret sharing scheme.

Shamir's secret sharing scheme allows you to split a "secret" into several "shares". You can only reconstruct the secret if you have a certain number of those shares. Any fewer, and it is impossible to deduce anything about the secret other than its length.

Step 1: Distribution

In this step, you will choose a secret. The secret is a string of text. It will be "split" into several shares. (These shares are also strings of text.) You can specify both the number of shares to produce and the number of shares you will need to reconstruct the secret.

For example, in a 3-of-5 scheme, you split your secret into five shares. Any three of them will allow you to reconstruct the original secret. If you only have one or two of those shares, though, you will have no way to recover or deduce any of the contents of that secret. 



        


        

            Step 2: Reconstruction
        


        

            Copy some of the text strings you obtained from above into the textbox below.
            Make sure that each share is separated with whitespace (e.g. a space or newline).
            If you enter enough shares for a given secret, you will see your message below.
            Otherwise, you will likely see garbage.
        


        

            
            
        


        

            
        


        

        

        


        

        

            Help
        


        

            Why do the shares look like they do?
        

        

            Let's analyze the share
            shamir-P6CFOD2J-11d-11-Nf8uJbgz8xKsBZA.
            
        


        

            

                
                    Part
                
                
                    Description
                
            

            

                
                    shamir
                
                
                    This is a prefix to help identify the data as belonging to a Shamir secret
                
            

            

                
                    P6CFOD2J
                
                
                    This is the secret's randomly generated ID. This is to help correlate many shares to the same
                    secret.
                
            

            

                
                    11d
                
                
                    This is the hex-encoded primitive polynomial used to generate the underlying Galois field. If you
                    don't understand what that means, that's okay. This is to give a nerd all the information they need
                    to write their own decoding algorithm. Most online tools do not report this, which means that
                    without their specific tool, you won't be able to reconstruct your secret. This tool gives you all
                    the information you need.
                
            

            

                
                    11
                
                
                    This is the x-coordinate used when reconstructing the polynomials.
                
            

            

                
                    Nf8uJbgz8xKsBZA
                
                
                    This is base64-encoded bytes that correspond to the y-values of a polynomials used in the algorithm.
                    Each byte uses a different polynomial, so we must keep track of a different y-value for each byte of
                    data.
                
            

        


        

            Note that this is all implementation-specific.
            I made some design decisions to make finding shares, using those shares, and reconstructing secrets easier.
            Many other online tools don't provide you with quite enough information to reconstruct the shares from
            scratch, and they rely on assumptions that aren't obvious by looking at, say, arbitrary byte strings.
        


        

            Can I trust this online tool?
        


        

            Technically, no.
            Don't use it for anything serious.
        

        

            That being said, I don't record any inputs.
            All of the computations are done locally in your browser.
            I compiled this code into WebAssembly and added a basic UI.
            You can verify that I don't send any information back to my server by monitoring any network requests in
            your developer tools.
        

        

            Also, you should never trust your sensitive information with random websites like this one. 😀
        


        

            Where can I see the underlying code?
        

        

            Check it out at https://github.com/49pctber/shamir.