# What is this encryption system called?

Let's say you want to break down a message, for simplicity it is just a bit $0$ or $1$, $m$ into two messages $(m_1, m_2)$ as follows:

If $m =0$, then $(m_1, m_2) = (0, 0)$ with probability $1/2$ and $(m_1, m_2) = (1,1)$ with probability $1/2$. Similarly, if $m=1$, then $(m_1, m_2) = (0,1)$ or $(1,0)$ each with probability $1/2$.

It's clear how the message can be retrieved from the two messages, and that nothing can be know from a single daughter message (each will be 0 or 1 with equal probability regardless of the mother message), unless the random number generator has a bias of sorts.

What is this system called?

(I don't do cryptography by trade, don't know which tags to use.)

• I'm not fully sure what you mean. Maybe it's the One-Time-Pad or a stream cipher. – SEJPM Aug 19 '15 at 14:02
• It looks to me to be a simple case of secret sharing, rather than encryption. – Bristol Aug 19 '15 at 14:45

For your scheme $m$ is then the secret, $m_1$ and $m_2$ are the shares and you need both shares to reconstruct the secret.
The scheme you describe is a well known and much used one, sometimes referred to as "XOR" sharing. This because you can define the shares as picking random bits $m_1, m_2$ under the restriction that $m = m_1 \oplus m_2$.