Cipher methods Symbols
Mirror Digits
Mirror digits are a graphic substitution cipher where each character is replaced by its image in a vertical mirror. It’s the classic childhood visual trick (writing a message backwards, reading it in a mirror), formalised in a table published on the dCode platform.
The dCode table covers 10 digits (0-9) and 10 Latin letters (A-J), 20 characters in total. Letters K-Z are not in the table and are marked as missing on CipherChronicle (rendered with a dash —). It’s therefore a limited cipher but visually immediate: the eye recognises most inverted characters (an inverted 3 remains recognisable, like a reversed E).
How does the cipher work?
The cipher relies on a monoalphabetic substitution: each cleartext character (digit 0-9 or letter A-J) is replaced by its mirror image. Same mechanic as the Caesar cipher (~50 BC), except the transformation is geometrically determined (vertical reflection) rather than chosen arbitrarily.
The table holds 20 glyphs (10 digits + 10 letters A-J). Letters K-Z are missing: the rendering uses a dash (—) to replace them, as for Bibi-binary, Friderici or Theraprism (see our entries).
Cryptographic strength: low. Monoalphabetic substitution → trivial frequency analysis. But reading is immediate once you look at the message in a real mirror — it’s a recreational rather than confidential cipher.
Historical and modern usage
- Children’s games — secret school messages.
- Escape rooms — using a physical mirror as a tool.
- Visual riddles — symmetry detection in cryptopuzzles.
- Geometric pedagogy — example of reflection transformation.
Related variants
- Caesar cipher — see our entry, alphabetic substitution.
- Atbash — see our entry, alphabetic mirror.
- Bibi-binary — see our entry, another cipher with missing letters.
What are the weaknesses?
- Frequency analysis — breaks it in a few dozen words.
- Mirror reading — instant decryption with a mirror.
- Missing K-Z — very partial alphabetic coverage.
The 20 glyphs
