Introduction
The Zodiac Killer mailed four cryptograms to Bay Area newspapers between 1969 and 1970, taunting police and daring cryptanalysts to crack them. Two have been solved. Two remain open. This interactive explorer lets you examine all four ciphers, study their symbol grids, attempt your own substitutions, and compare your work against the verified solutions. The Z408 cipher was broken in a week by a schoolteacher and his wife. The Z340 resisted every attack for 51 years until a team of three volunteer codebreakers cracked it in December 2020. The Z13 and Z32 ciphers remain unsolved to this day, and recent academic analysis suggests they may be structurally unsolvable.
What this tool does
- Displays all four Zodiac ciphers (Z408, Z340, Z13, Z32) as interactive symbol grids you can click and inspect.
- Lets you assign a plaintext letter to any cipher symbol and watch every instance update across the entire grid in real time.
- Shows the verified FBI-confirmed solution for Z408 and Z340 with a single click, so you can compare your work to the known answer.
- Provides a substitution table listing every unique symbol with its current assignment, giving you a complete overview of your decryption attempt.
- Includes historical context for each cipher: mailing date, solver, method, and why the unsolved ones resist analysis.
How this tool works
The tool loads hardcoded transcriptions of the original cipher symbols using the Webtoy ASCII encoding from the Zodiac Killer Ciphers Wiki. Each cipher renders as a grid matching its original dimensions: Z408 is 17 columns by 24 rows, Z340 is 17 columns by 20 rows, Z13 is a single row of 13 characters, and Z32 is two rows totaling 32 characters.
Click any symbol in the grid to select it, then type a letter to assign it. Every occurrence of that symbol across the entire grid updates instantly. The substitution table below the grid shows all unique symbols and their current assignments side by side. Your decryption attempt appears in a text area that formats decoded letters into words. For Z408 and Z340, a "Show known solution" button reveals the verified plaintext so you can check your progress against the real answer.
How the cipher or encoding works
The Zodiac ciphers use homophonic substitution, a technique where each plaintext letter maps to multiple cipher symbols. This defeats simple frequency analysis because the most common letter (E) can be represented by eight or more different symbols, flattening the frequency distribution. The Zodiac used 54 distinct symbols in Z408 and 64 in Z340, far more than the 26 letters in the English alphabet.
Z408 was solved on August 8, 1969 by Donald and Bettye June Harden, a schoolteacher couple from Salinas, California. They exploited the killer's predictable double-letter patterns (LL in KILL, THRILL, WILL) and his habit of starting messages with "I". The cipher contains deliberate misspellings like "ANAMAL" for "animal" and "FORREST" for "forest". The last 18 characters ("EBEORIETEMETHHPITI") do not decode to meaningful text and may be filler or a dropped line.
Z340 was solved on December 5, 2020 by David Oranchak, Sam Blake, and Jarl Van Eycke. The breakthrough came after 51 years because the cipher has two layers: a homophonic substitution and a diagonal transposition. The grid splits into three segments of 9, 9, and 2 rows. The first two segments use a "knight's move" reading order (down one row, across two columns), while the third segment reads normally. The phrases "LIFE IS" and "DEATH" appear untransposed at the end of the last two lines. The FBI validated the solution on December 12, 2020.
Z13 and Z32 remain unsolved. A 2026 paper published on Zenodo (DOI: 10.5281/zenodo.19104092) argues that Z13 and Z32 form a "structural anti-cipher" system: symbolic constructions that resemble ciphers but encode permanent ambiguity rather than recoverable plaintext. Whether this interpretation is correct or not, the mathematical reality is that 13 characters with 8 unique symbols and 32 characters with 29 unique symbols are too short to verify any proposed solution beyond reasonable doubt.
How to use this tool
- Select a cipher from the dropdown at the top. Z340 is a good starting point because its solution is well documented.
- Click any symbol in the grid to highlight all instances of that symbol. A text field appears where you can type your guessed letter.
- Watch the grid update in real time. Every cell sharing that symbol changes to show your assigned letter.
- Use the substitution table below the grid to track all your assignments and spot patterns across the unique symbols.
- For solved ciphers (Z408, Z340), click 'Show known solution' to reveal the verified plaintext and compare it to your attempt.
- Click 'Reset' to clear all substitutions and start over, or switch to an unsolved cipher (Z13, Z32) to try your own hand at cracking it.
Real-world examples
Cryptography class: homophonic substitution lab
A professor assigns students to crack Z408 using the same techniques the Hardens used in 1969. Students identify the doubled L pattern in words like KILL and THRILL, then use frequency analysis on the remaining symbols. The explorer lets them test hypotheses in real time without pencil and paper, and the solution button provides instant verification.
True crime community: Z340 transposition analysis
A true crime researcher uses the Z340 grid to study the diagonal transposition that stumped cryptanalysts for 51 years. By assigning letters from the known solution, they can see how the knight's move reading order scrambles the plaintext across the three segments. The visual grid makes the transposition pattern immediately apparent compared to reading a flat text transcription.
Amateur cryptanalyst: attempting Z13
A hobbyist cryptanalyst selects Z13 and experiments with different letter assignments for the three circled-8 symbols that dominate the center of the cipher. The tool shows that with only 13 characters and 8 unique symbols, dozens of plausible names fit the constraints equally well, illustrating why short ciphers are mathematically underdetermined.
Comparison with similar methods
| Method | Complexity | Typical use |
|---|---|---|
| Z408 (homophonic substitution) | Medium | Single-layer substitution with 54 symbols, solved in 1 week |
| Z340 (substitution + transposition) | High | Two-layer cipher with diagonal transposition, solved in 51 years |
| Z13 (My name is) | Unsolvable | 13 characters, 8 unique symbols, mathematically underdetermined |
| Z32 (Map code) | Unsolvable | 32 characters, 29 unique symbols, severely underdetermined |
Limitations or considerations
The Z13 and Z32 ciphers are almost certainly unsolvable, and not for lack of effort. Dozens of researchers have proposed solutions over five decades, and none has achieved consensus. The problem is mathematical: Z13 has only 13 characters with 8 unique symbols, meaning any solution that permits anagramming has billions of valid candidates. Z32 has 32 characters with 29 unique symbols, providing almost no repeated patterns to anchor analysis. A 2023 IACR ePrint paper (2023/982) by F. Foxon formalized the coordinate hypothesis for Z32 but concluded that no determinate decoding exists within the defined solution space. A 2026 Zenodo paper went further, defining Z13 and Z32 as "anti-ciphers" that encode terminal undecidability rather than recoverable content.
This tool uses ASCII transcriptions of the original symbols, which cannot capture every visual nuance of the Zodiac's handwriting. Some symbols in the original ciphers are ambiguous or merged, and different transcriptions exist. The Webtoy encoding used here is the most widely accepted standard in the research community. For the solved ciphers, the solutions shown include the killer's original misspellings (PARADICE, ANAMAL, EXPERENCE) preserved exactly as the FBI validated them.
Frequently asked questions
Who solved the Z340 cipher?
David Oranchak, Sam Blake, and Jarl Van Eycke solved Z340 on December 5, 2020, after 51 years. Oranchak is a software developer in Virginia, Blake is an applied mathematician in Melbourne, and Van Eycke is a programmer in Belgium. They used a combination of diagonal transposition analysis and the AZdecrypt homophonic substitution solver. The FBI validated the solution on December 12, 2020.
Why did Z340 take 51 years to solve?
Z340 has two encryption layers: homophonic substitution and a diagonal transposition that splits the grid into three segments with different reading orders. Standard homophonic substitution solvers like AZdecrypt could not crack it because the transposition scrambles the letter order. The breakthrough came when the team discovered that splitting the cipher into three vertical segments of 9, 9, and 2 rows and applying a knight's move reading order to the first two segments produced text that AZdecrypt could solve.
Can Z13 or Z32 ever be solved?
Probably not with confidence. Z13 has only 13 characters with 8 unique symbols, and Z32 has 32 characters with 29 unique symbols. Both are too short to verify any proposed solution beyond reasonable doubt. A 2026 academic paper formally proved that Z32 has no determinate decoding within the coordinate hypothesis solution space. Dozens of proposed solutions exist for both, but none has achieved consensus.
What is homophonic substitution?
Homophonic substitution assigns multiple cipher symbols to each plaintext letter. High-frequency letters like E receive more symbols than rare letters like Z. This flattens the frequency distribution and defeats simple frequency analysis. The Zodiac used 54 symbols for 26 letters in Z408 and 64 symbols in Z340, making frequency patterns much harder to detect than in a simple substitution cipher.
What do the last 18 characters of Z408 mean?
The last 18 characters of Z408 decode to 'EBEORIETEMETHHPITI' using the Harden key, which is gibberish. The most likely explanation is that the Zodiac dropped a line from his original message when copying the third part, leaving 18 filler characters to maintain the grid shape. Some researchers believe these characters contain a hidden secondary message, but no convincing interpretation has been proposed.
Conclusion
The Zodiac ciphers represent one of the most fascinating intersections of true crime and cryptography in history. Z408 showed that a determined amateur could break a homophonic substitution cipher in days. Z340 demonstrated that adding a transposition layer can stump the world's cryptanalysts for half a century. Z13 and Z32 illustrate the fundamental limits of cryptanalysis: when a cipher is too short, no amount of computing power can distinguish the correct solution from billions of plausible alternatives. This explorer brings all four ciphers to your screen with verified transcriptions, interactive substitution tools, and the FBI-confirmed solutions for the two that have been cracked. To study related ciphers on this site, try the homophonic substitution cipher or the cipher identifier. For deeper research, the Zodiac Killer Ciphers Wiki maintained by David Oranchak is the definitive resource.