Beyond the Basics
While Caesar ciphers and Vigenère are common, puzzle cache owners often use more obscure ciphers to increase difficulty. This guide covers the techniques you need to decode them.
Pigpen Cipher & Variants
The Pigpen cipher (also called the Masonic cipher) uses a grid-based substitution where letters are represented by portions of the grid.
Standard Pigpen
Letters A-I and J-R go in two tic-tac-toe grids. Letters S-V and W-Z go in two X-shaped grids with dots. Each letter is represented by the lines surrounding its position.
Standard Pigpen grid positions:
A B C J K L D E F M N O G H I P Q R S W T U X Y V Z
Common Variants
- Templar Cipher: Similar structure but different grid arrangement. Try our Templar Cipher tool.
- Rosicrucian Cipher: Uses triangles instead of grids.
- Rotated Pigpen: Standard Pigpen but the entire key is rotated 90°, 180°, or 270°.
- Custom Order: Letters placed in grid in non-standard order (reverse, keyword-based, etc.).
Solving Tip: If standard Pigpen doesn't work, try rotating your interpretation or look for a keyword hint in the cache description that might indicate a custom alphabet order.
Nihilist Cipher
The Nihilist cipher was used by Russian revolutionaries. It combines a Polybius square with a numeric key for double encryption.
How It Works
- Create a 5×5 Polybius square (I and J share a cell)
- Convert plaintext to two-digit numbers using the grid
- Convert the keyword to numbers the same way
- Add the plaintext numbers to the repeating keyword numbers
Standard Polybius Square:
1 2 3 4 5 1 A B C D E 2 F G H I K 3 L M N O P 4 Q R S T U 5 V W X Y Z
Example: "HELLO" = 23 15 31 31 34
Recognition Signs
- Output is two-digit numbers, often in the range 22-99
- Numbers rarely start with 1 (only if both digits from squares are 1)
- Some numbers are impossible (11, 16, 17, etc. depending on key)
Porta Cipher
The Porta cipher is a polyalphabetic cipher that uses 13 alphabets. Unlike Vigenère, it's reciprocal — the same operation encrypts and decrypts.
Key Characteristics
- Uses a keyword like Vigenère
- Pairs of letters (AB, CD, EF, etc.) select the same alphabet
- Only swaps letters in the second half of the alphabet (N-Z) with letters in the first half (A-M)
- Self-reciprocal: encrypt and decrypt are the same operation
Recognition Signs
- If you know it's polyalphabetic but Vigenère doesn't work, try Porta
- Letter frequency will be flatter than plaintext (like Vigenère)
- Look for hints about "reciprocal" or "self-inverse" in the cache description
Bifid & Trifid Ciphers
Bifid Cipher
The Bifid cipher combines substitution with transposition using a Polybius square.
- Convert each letter to row/column coordinates from a 5×5 grid
- Write all row numbers, then all column numbers
- Read off pairs and convert back to letters
Example with "HELLO":
H=23, E=15, L=31, L=31, O=34 Rows: 2 1 3 3 3 Columns: 3 5 1 1 4 Combined: 2 1 3 3 3 3 5 1 1 4 Pairs: 21 33 33 51 14 = F N N V D
Trifid Cipher
The Trifid cipher extends this concept to three dimensions using a 3×3×3 cube, allowing for 27 characters (alphabet + one symbol).
Recognition Signs
- Very flat frequency distribution (combines substitution + transposition)
- Ciphertext length equals plaintext length
- Often mentioned alongside "Polybius" or "grid" in cache hints
Four-Square & Two-Square Ciphers
Four-Square Cipher
The Four-Square cipher uses four 5×5 grids arranged in a square. Two contain the standard alphabet, two contain keyed alphabets.
Four-Square arrangement:
[Standard] [Keyed 1] [Keyed 2] [Standard]
Two-Square Cipher
The Two-Square cipher is simpler, using only two 5×5 grids (one standard, one keyed) arranged horizontally or vertically.
Recognition Signs
- Encrypts pairs of letters (digraphs)
- Ciphertext length is always even
- Similar to Playfair but with multiple grids
ADFGVX Cipher
The ADFGVX cipher was used by Germany in WWI. It's a fractionating transposition cipher that produces ciphertext containing only the letters A, D, F, G, V, and X.
How It Works
- Create a 6×6 grid with rows/columns labeled A, D, F, G, V, X
- Fill grid with a keyed alphabet (26 letters + 10 digits)
- Replace each character with its row+column letters
- Apply columnar transposition with a keyword
Recognition Signs
- Only contains letters A, D, F, G, V, X — this is unmistakable!
- Ciphertext is roughly twice the length of plaintext
- ADFGX variant uses only 5 letters (no V) for a 5×5 grid
Beaufort Cipher
The Beaufort cipher is similar to Vigenère but with a crucial difference: instead of adding the key to the plaintext, it subtracts the plaintext from the key.
Key Difference from Vigenère
- Vigenère: C = P + K (mod 26)
- Beaufort: C = K - P (mod 26)
- Beaufort is reciprocal — same operation encrypts and decrypts
Solving Tip: If a puzzle looks like Vigenère but standard decryption produces gibberish, try Beaufort with the same key. Many puzzle setters use this as a twist.
Fractionated Morse Cipher
The Fractionated Morse cipher converts text to Morse code, then enciphers the dots, dashes, and spaces.
How It Works
- Convert plaintext to Morse code with 'x' between letters, 'xx' between words
- Group into trigraphs (groups of 3 symbols)
- Substitute each trigraph with a letter using a keyed alphabet
Recognition Signs
- Ciphertext is approximately 70% the length of the Morse code representation
- Look for references to Morse in the cache description
- May see hints about "fractionation" or "trigraphs"
General Strategy for Unknown Ciphers
- Analyze the character set. What characters appear? Only A-F? Only ADFGVX? This often identifies the cipher immediately.
- Check the length. Is it doubled, halved, or same as expected plaintext?
- Run frequency analysis. Use our Letter Frequency Analyzer. Flat distribution suggests polyalphabetic or fractionating cipher.
- Look for keywords in the cache. "Key", "square", "grid", "WWI", "reciprocal" all hint at specific cipher types.
- Try multiple tools systematically. Start with the most common (Vigenère, Playfair) then move to obscure ones.