Keyless Crypto: How Do Bob, Alice and Carol Share A Secret Message?
Just imagine you could get perfect security, and not have to store encryption keys?
A problem with encryption, is when someone gets our encryption key. So can we do keyless crypto, where we do not need a key to decrypt an encrypted message? Well, yes, with secret shares we can, and where we cipher a message into secret shares, and only when these shares are brought back together can we recover the message.
For example, let’s say that Bob has two secret shares. He stores one share on his computer, and the other one in a Dropbox folder. Then only when they are brought together will the file be recovered. Anyone looking in his Dropbox folder, will not be able to decrypt it, as there is no key, and the only thing that will bring it back is the other share.
So, let’s take an example of having three shares, and give them to Bob, Alice and Carol. Then, only if they all come together, will the secret be revealed. In this case we will keep it simple and just use RSA for the shares.
With standard RSA, we create two prime numbers (p and q). and then calculate the modulus:
We then have Euler’s totient function:
