Atbash Cipher (English)

Summary: A simple substitution cipher where the alphabet is reversed. First letter <-> Last letter (A<->Z, B<->Y, C<->X, etc.). This is a reciprocal cipher.

Alphabet Mapping:

Plain:  A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Cipher: Z Y X W V U T S R Q P O N M L K J I H G F E D C B A

Example:

• Plaintext: MEET AT NOON
• Process:
  • M -> N, E -> V, E -> V, T -> G
  • A -> Z, T -> G
  • N -> M, O -> L, O -> L, N -> M
• Ciphertext: NVVG ZG MLLM

Decryption: Apply the same transformation (Atbash is its own inverse).

Additional Example:

• Plaintext: THE QUICK BROWN FOX
• Letter by letter conversion:
  • T->G, H->S, E->V
  • Q->J, U->F, I->R, C->X, K->P
  • B->Y, R->I, O->L, W->D, N->M
  • F->U, O->L, X->C
• Ciphertext: GSV JFRXP YILDM ULC

Decrypting back:

• Ciphertext: GSV JFRXP YILDM ULC
• Apply Atbash again:
  • G->T, S->H, V->E
  • J->Q, F->U, R->I, X->C, P->K
  • Y->B, I->R, L->O, D->W, M->N
  • U->F, L->O, C->X
• Plaintext: THE QUICK BROWN FOX

Pattern Recognition: Notice that letters in the middle of the alphabet stay close to middle:

• M <-> N (positions 13 and 14)
• This is why ROT13 (Caesar shift 13) and Atbash can look similar for middle letters