ROT-5 Cipher

Rot 5 encryption applies on the numbers in a message. It involves replacing a digit by another by adding 5 (modulo 10).

Example: 1234567890
6789012345

Example: 248 is crypted 793 by ROT-5

For letters, the corresponding symmetric cipher is Rot-13

Decryption of Rot5 is identical to the encryption because Rot5 is reversible.

Example: 1234567890
6789012345

Example: 793 re-becomes 248

ROT-5 is used on the digits. Numbers that began with 1 now begin with 6 etc.

According to Benford's law, there should be more 6 than 4 in the ciphertext.

Rot-5 is already a variant of Rot13, itself a version of Caesar cipher with a shift of 13. Rot-5 is therefore a Caesar cipher with a shift of 5, but applied to the digits.

It is common to associate a ROT-13 for coding the letters and ROT-5 for the numbers at the same time.

A shift of 5 allows the code to be reciproqual/reversible/symmetric, this means that 2 consecutive encryptions lead to find the plain number.