Atbash

For example, the Hebrew alphabet would work like this: Because there is only one way to perform this, the Atbash cipher provides no communications security, as it lacks any sort of key.

If multiple collating orders are available, which one was used in encryption can be used as a key, but this does not provide significantly more security, considering that only a few letters can give away which one was used.

The Atbash cipher for the modern Hebrew alphabet would be: By shifting the correlation one space to the left or the right, one may derive a variant Batgash (named for Bet–Taw–Gimel–Shin) or Ashbar (for Aleph–Shin–Bet–Reish).

Either alternative mapping leaves one letter unsubstituted; respectively Aleph and Taw.

Under the standard affine convention, an alphabet of m letters is mapped to the numbers 0, 1, ... , m − 1.