Variable Shift Cipher

Each letter shifts by its position number (1st +1, 2nd +2, etc.).

Learn

Each letter shifts by its position number (1st +1, 2nd +2, etc.).

Unlike the Caesar cipher where all letters shift by the same amount, the variable shift cipher uses position-dependent shifting. The first letter shifts by 1, the second by 2, and so on. This makes the cipher harder to break since the same letter can encode differently based on its position.

Letter at position N shifts forward by N positions. Position 1: +1, Position 2: +2, Position 3: +3, etc.

CAT -> D(C+1) C(A+2) W(T+3) = DCW
HELLO -> I(H+1) G(E+2) O(L+3) P(L+4) T(O+5) = IGOPT

How to recognize it

Different shifts for each position
First letter always shifts by 1
Pattern: 1st +1, 2nd +2, 3rd +3...

Common mistakes

Using same shift for all letters
Forgetting to wrap around Z back to A
Miscounting positions (starting from 0 vs 1)

Step-by-step walkthrough

Encode 'CAT' with variable shift (position 1 = +1, position 2 = +2, etc.)

C is at position 1. Shift by +1: C (3rd letter) + 1 = D
A is at position 2. Shift by +2: A (1st letter) + 2 = C
T is at position 3. Shift by +3: T (20th letter) + 3 = W

Answer: DCW

Practice guidance

Coding & Decoding