I personally don't really agree with the one-time pad theory but if we're going to go down that road then here is how an OTP works. I quote from a book on quantum information theory I bought back when I was less skint. Terminology - Alice is sending the message, Bob is receiving the message, Eve is an eavesdropper trying to decode the message.
The first and simplest cipher to achieve perfect secrecy was the Vernam cipher, or one-time pad. The central idea is that the rule for transposing or substituting the letters changes for each symbol and never
repeats. In the digital age, all messages are represented by a string of binary digits. Alice’s message is encoded in this bit string, using a system such as ASCII, and it is this string that constitutes the plaintext. ASCII, or the American Standard Code for Information Interchange, maps 128 distinct symbols onto the 128 different seven bit strings 0000000 to 1111111. For example, the 26 upper-case letters, A, B, ···, Z, correspond to the binary strings 1000001, 1000010, ···, 10011010, and the lower-case letters, a, b, ···,z,are represented by the numbers 1100001, 1100010, ···, 1111010. Any message of
m characters (including spaces) will correspond to a continuous string of
7m bits, with spaces between words encoded as the string 1011100.
Let us suppose that all of the possible messages are encoded as strings of
N bits so as to be indistinguishable on the basis of length alone. Shorter messages can be increased to
N bits, for example by adding zeros or the ASCII code for the suitable number of spaces. The Vernam cipher uses a key of
N randomly chosen bits and its security relies entirely on the secrecy of this, which should ideally be known only to Alice and Bob. The ciphertext is created by modulo 2 addition, which we denote by ⊕:
- Code: Select all
0⊕0=0
0⊕1=1
1⊕0=1
1⊕1=0
Performing this addition bit by bit between the plaintext and the key generates the ciphertext:
- Code: Select all
P = ...001011010...,
K = ...101110100...,
C = P ⊕ K = ...100101110...
We can see from the above example that modulo 2 addition on each bit either leaves the bit the same, or flips the bit, and if the key is random then then each of these events occurs with probability one half. The nett effect is that the ciphertext itself reflects the random nature of the key, in that to anyone without access to the key the ciphertext is random and hence carriers no information about the plaintext.
... the book then shows mathematically that Shannon's criterion for perfect secrecy is satisfied by this result, and then Shannon's noisy coding theorem tells us that no information about the plaintext is carried by C alone. Recovering the information is therefore only possible once you have the key.
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So what does all this mean in relation to the RSD key? It is either a mathematical challenge, or a password for a website, or one of these other theories - or the key to an existing ciphertext to be revealed. If you must believe it is an OTP then the fact it is all numerical makes it unlikely that the coding mechanism is ASCII, so drop that. As you can see the OTP operation is performed on bits, and the number of bits required to represent 1-9 (so far, no zeros) is four 0000 - 1111 = 1+2+4+8 = 15.
It's possible that some messages are keys and some messages are ciphertexts also, and there may be some way to differentiate. I won't be going down that road though because I dunno, it seems rather odd (read completely mental) that you'd need to pick up a graduate level physics textbook to solve the problem.