TL;DR: Start with A1Z26 numbers, then add arithmetic shifts, keyword reordering, or custom maps. Document your key so teammates decode consistently.
A1Z26 as the engine
Most classroom substitution starts by converting letters to numbers, transforming numbers, then converting back. The transform defines the cipher strength.
Caesar shift on numbers
Add 3 to each value, wrap with mod 26 (replace 27 with 1, etc.), decode by subtracting 3. Plain A1Z26 is Caesar shift of zero.
Keyword column ciphers
Write a keyword without repeats (CIPHER → C,I,P,H,E,R), append remaining alphabet letters, assign 1–26 to that column order. A maps to whatever letter sits at position 1 in the shuffled strip.
Atbash numeric form
Replace value v with 27−v. A=1 becomes 26 (Z). Symmetric encode and decode.use the same formula.
Puzzle hunt layering
Designers encode A1Z26, then anagram, then hide numbers in images. Solvers peel layers backward. Label your puzzle “numeric substitution” if only A1Z26 is used to avoid overthinking.
Spreadsheet helper columns
Column A letters, B A1Z26, C shifted values, D decoded letters via VLOOKUP. Teach students structure before they touch formula-less tools.
Verify with the baseline tool
Before applying shifts, confirm plain A1Z26 on letterstonumbers.com. Shift bugs hide in bad base encoding more often than in shift math.
Security expectations in class
Substitution homework demonstrates concepts, not bank-grade encryption. Discuss why modern apps use keys measured in bits, not alphabet positions.
Group exercise: design your own map
Teams publish a scrambled alphabet strip and exchange messages. Compare decode difficulty against plain A1Z26—usually one extra step stumps casual peekers only.
When substitution fails readability
Numbers above 26 after custom rules signal wrap errors. Mod 26 aggressively and retest on a three-letter word before encoding paragraphs.
Caesar shift on numeric values
Add three to each A1Z26 value, wrap with mod 26 using ((v−1)+shift) mod 26 + 1 on 1-based indexing. Test A and Z before encoding paragraphs.
Keyword column construction
Write keyword without repeated letters, append remaining alphabet, assign 1–26 to new order. A maps to whichever letter sits at position one in shuffled strip.
Atbash numeric symmetric form
Replace value v with 27−v. Encode and decode use identical formula—elegant homework extension after plain A1Z26 unit.
Spreadsheet pipeline teaching
Columns: letter, A1Z26, shifted value, decoded letter via lookup. Verify plain encoding on https://letterstonumbers.com/ before teaching shift formulas.
Puzzle hunt layering etiquette
Label clues ‘numeric substitution’ when only A1Z26 is used. Solvers over-engineer exotic methods when labels are vague.
Adding three to every number in MAPLE
MAPLE is a clean shift demo because none of its letters sit so close to Z that the first trial wraps. M is 13, A is 1, P is 16, L is 12, E is 5. Add 3 to each value and you get 16 4 19 15 8, which decodes to PDSQH. The word is nonsense on purpose. Students who “fix” it back into a real word have undone the shift. The record you keep is the pair: base MAPLE, shift plus 3, result PDSQH.
Now push a letter over the edge. Encode ZEBRA first: 26 5 2 18 1. Add 3: 29 8 5 21 4. 29 is not a letter. Subtract 26 once and 29 becomes 3, so the wrapped row is 3 8 5 21 4, which is CHEUD. Write the wrap rule next to the addition: if the sum is greater than 26, subtract 26 once. Do not subtract 26 from every number. Students who wrap M as well will turn MAPLE into a different cipher and the two examples will no longer agree.
Writing the key on the same card as the numbers
A layered cipher without a key line is a lost afternoon. On the card, print three labeled rows: WORD, A1Z26, PLUS 3. For MAPLE the middle row is 13 1 16 12 5 and the bottom row is 16 4 19 15 8. A teammate who receives only the bottom row cannot know whether you added 3, added 1, or used a keyword. The label is part of the cipher for classroom work. Hide the label only when the puzzle instructions already said “each number is three past alphabet position.”
Test the card by covering the word and decoding from the bottom with the written rule. You should land on MAPLE, not on PDSQH. If you land on PDSQH, you decoded the shifted numbers as if they were plain A1Z26. That mistake is the most common one in hunt writeups. The fix is procedural: always undo the arithmetic before you look up letters.
Inverse step that returns MAPLE from PDSQH
Start from 16 4 19 15 8 and subtract 3 from each value. You get 13 1 16 12 5, then M A P L E. Do this inverse on paper before you add any wrap example. Students who only practice the forward direction cannot undo a hunt clue. The inverse is the skill they actually need when someone else chose the shift.
When a value would fall below 1, add 26. Decoding CHEUD, which was ZEBRA plus 3, the first value is 3. Subtract 3 and you get 0, then add 26 to reach 26, which is Z. Walk that single cell on the board until the 0 never survives as a final answer. A lingering 0 means the inverse rule was remembered as “subtract and hope.”
Minus-four wrap on the second letter of WALNUT
WALNUT is a reverse-shift drill that fails in a different place than a word starting near Z. W is 23, A is 1, L is 12, N is 14, U is 21, and T is 20. Subtract 4 from each value. W lands on 19. A lands on negative 3, so add 26 once and call that cell 23. L becomes 8, N becomes 10, U becomes 17, and T becomes 16. The row is 19 23 8 10 17 16, which spells SWHJQP. Add 26 only to the cell that went negative. Adding 26 to every letter invents a second cipher, and the card will no longer match this row.
Undo the row by adding 4. The second cell is 23 plus 4, which is 27. Subtract 26 once and you are back at 1, the letter A. The other cells return to 23, 12, 14, 21, and 20, which is WALNUT. If the class reads SWHJQP as the recovered word, they named letters before they undid the shift. Say the order out loud on the first two cells, then stop when 27 becomes 1. That single wrap is the reason this word is on the card.
