HOW TO SEND A PIN CODE SECRETLY
Step 1:
Tell your correspondent to silently choose a 4-digit number and to write it down.
Tell them to call this A and to keep this private at all times, including from you.
A: Correspondent’s Private key = [not known to you]
YOU: Choose a 4-digit PIN number. Keep this private at all times. Call this B
B: Your Private key =
YOU: Choose another 4-digit number.
Call this X.
Tell X to your correspondent and tell them to write it down.
X: Public key =
Step 2: YOU
YOU: Multiply your Private number B by the Public number X. This will be a very long number!
Call this BX
BX:
YOU: Underline the last 4 digits of BX
Call this Y
Y:
YOU: Give Y to your correspondent and tell them to call it Y
Step 3: INSTRUCTING YOUR CORRESPONDENT
Tell your correspondent to multiply A by X. This will be a very long number!
Tell them to call this AX
AX: [not known to you]
Tell them to underline the last 4 digits of AX
Tell them to call this C
Ask for your correspondent’s number C and write it here
C:
Step 4: YOU
Multiply C by your private number B.
Call this BC
BC:
Underline the last 4 digits of BC.
Call this D. NB this must never be transmitted
D:
Step 5: INSTRUCTING YOUR CORRESPONDENT
Tell your correspondent to multiply Y by their private number A.
Tell them to call this Z
AY = Z: [not known to you]
Tell your correspondent to underline the last 4 digits of Z.
Tell them to call this E. Tell them this must never be transmitted
E: [not known to you]
Step 6: YOU
Multiple D by the PIN you want to send secretly.
Call this G.
D x _ _ _ _ = G:
Step 7: INSTRUCTING YOUR CORRESPONDENT
YOU: Give G to your correspondent
Tell your correspondent to divide G by E.
Tell them to call this H (H = G/E). This is the PIN you transported secretly
H: _ _ _ _