Atbash Cipher Tool

The Mirror Pair Table (Latin Atbash)

Atbash is defined by 13 mirror pairs. Each plain letter swaps with its partner across the alphabet:

The Original Hebrew Atbash

The cipher's name comes from its own Hebrew description: Aleph (א) maps to Tav (ת), Beth (ב) maps to Shin (ש). Spell those four letters together: A-T-B-Sh → אתבש → Atbash. Here are the eleven Hebrew mirror pairs:

How to Use the Atbash Cipher Tool

1. Type or paste your plain text or Atbash ciphertext into the input box. The live mirror visualization on the right pairs the latest letter with its mirror partner in real time.
2. Pick a variant. Atbash mirrors Latin letters only. Atbash + Digits also mirrors 0-9 onto 9-0 — useful for hiding ID numbers along with words. Hebrew Atbash applies the original biblical mapping to Hebrew text.
3. Click Apply Atbash. The full output appears below with the character-by-character mirror, a unique-substitution grid, statistics, and a round-trip proof that Atbash is its own inverse.
4. Use the Copy buttons to grab the ciphered text or the original. To decode Atbash, paste the ciphertext and click Apply Atbash again — no separate decode button is needed.

Three Variants Explained

The Babel → Sheshach Example (Jeremiah 25:26)

The earliest documented use of Atbash is in the Book of Jeremiah, where the prophet hides the name Babel (Babylon) as Sheshach. In Hebrew, Babel is spelled בבל (B-B-L). Under Atbash:

• ב (Beth) ↔ ש (Shin)
• ב (Beth) ↔ ש (Shin)
• ל (Lamed) ↔ כ (Kaph)

So בבל becomes ששך — read as Sheshach. This is exactly the disguised name that appears in Jeremiah 25:26 and 51:41 of the Hebrew Bible. Try the "Babel → Sheshach" quick example above to see it in the live preview.

Why Atbash Is Its Own Inverse

Atbash is an involutory cipher because mirroring twice is the identity. Number the letters 0 through 25. The Atbash function is \( f(i) = 25 - i \). Applying it twice gives \( f(f(i)) = 25 - (25 - i) = i \), so you return to the start. The same identity holds for the digit mirror \( g(d) = 9 - d \) and for the 22-letter Hebrew alphabet \( h(i) = 21 - i \). One button encodes and decodes.

Atbash vs Caesar vs ROT13 — Quick Reference

The key difference: Caesar and ROT13 slide every letter by the same amount; Atbash reflects. With Atbash, A and Z swap (largest jump), while M and N swap (smallest jump). With Caesar/ROT13, every letter moves the same distance.

Hand-Computing Atbash in One Line

For Latin letters, the formula is: output = (25 − position) + 'A'. To do it in your head: count how far the letter is from A, then count back the same distance from Z. Examples:

• A is position 0 → mirror is at position 25 from A → Z.
• H is position 7 → mirror is at position 25 − 7 = 18 → S.
• M is position 12 → mirror is at 25 − 12 = 13 → N. The middle pair barely moves.
• Z is position 25 → mirror is at 0 → A. Symmetric.

Where Atbash Is Used Today

• Biblical scholarship. Researchers translating the Hebrew Bible use Atbash to decode words like Sheshach (=Babel) and Leb Kamai (=Kasdim/Chaldea) in Jeremiah.
• CTF and puzzle challenges. Capture-the-flag organizers often start with Atbash as a warm-up before harder classical-cipher rounds.
• Escape rooms and ARGs. Game designers like Atbash because it needs no key and is easy to print on a single card.
• Teaching cryptography. Atbash is the simplest non-trivial reflection cipher and is widely used in cryptography lectures alongside Caesar.
• Spoiler protection. Like ROT13, Atbash hides text from a casual glance — but with a different visual signature, so it adds variety.

Security Notice

Atbash is not encryption. It is a reversible transformation that anyone can undo in seconds — by hand, on paper, or with a one-line script. There is no key, so the same mapping is shared by every user. Never use Atbash to protect passwords, personal data, financial information, or anything that should stay confidential. For real protection, use modern cryptography such as AES-256, ChaCha20, RSA, or libsodium. Treat Atbash as a way to obscure text, not to secure it.

Tips for Best Results

• To decode Atbash ciphertext, paste it and click Apply Atbash again — the same button works because the cipher is self-inverse.
• For mixed text with letters and numbers, use Atbash + Digits to also disguise the numbers.
• If you want every letter to look the same regardless of case, untick "Preserve original case" and the tool will normalize to UPPER before mirroring.
• For Hebrew Bible study, choose Hebrew Atbash and paste Hebrew text — final-form letters (ך, ם, ן, ף, ץ) are normalized to their standard forms before mirroring.
• Non-ASCII characters that are not in the chosen alphabet (accented letters, CJK, emoji) pass through unchanged in every variant.

FAQ

What is the Atbash cipher?

Atbash is one of the oldest known substitution ciphers. It replaces every letter with its mirror across the alphabet — A becomes Z, B becomes Y, C becomes X, and so on. The cipher originated in ancient Hebrew, where Aleph (the first letter) maps to Tav (the last) and Beth maps to Shin. The name "Atbash" itself is built from these letters: A-T-B-Sh.

How does Atbash differ from ROT13 or Caesar?

Caesar and ROT13 are rotation ciphers — every letter shifts by the same offset (3 for classical Caesar, 13 for ROT13). Atbash is a reflection cipher — letters near the start map to letters near the end, while letters in the middle barely move (M↔N). Atbash has no key, while Caesar's key is the shift amount.

Is Atbash secure for real encryption?

No. Atbash has no key and only 26 possible letters, so it is trivially broken by frequency analysis or by simply trying the cipher once. Use it for puzzles, teaching, spoilers, and CTF warm-ups, not for protecting anything confidential.

Why is Atbash its own inverse?

Atbash is involutory because mirroring twice returns the original. If A maps to Z, then Z maps back to A. Mathematically, the mapping is \( f(i) = 25 - i \), and \( f(f(i)) = 25 - (25 - i) = i \). The same one-button operation encodes and decodes.

Where is Atbash used in the Bible?

The Book of Jeremiah uses Atbash to hide the name "Babel" (Babylon) as "Sheshach" (Jeremiah 25:26 and 51:41). The Hebrew letters of Babel — B-B-L — map under Atbash to Sh-Sh-K, which yields the disguised place name. This is the earliest documented use of the cipher.

Does Atbash preserve case and punctuation?

Yes. Uppercase letters map to uppercase, lowercase to lowercase. Spaces, digits, and punctuation pass through unchanged unless you switch to the Atbash + Digits variant, which also mirrors 0-9 onto 9-0.