Vigenere Multiplicative Cipher

Encryption uses a numeric key (some numbers) and a numeric message (use a alphanumeric substitution, or ascii code for example).

Example: Encode 4,3,15,4,5 (for DCODE) with the key 11,5,25 (for CLE)

Take the first number of the message and the first number of the key and multiply them, the result is the product's value. Same for the next numbers of the message and the key.

If the key length is inferior of the text lenght, start over the key.

Example: Calculate 4*11=44, 3*5=15, 15*25=375, 4*11=44, 5*5=25 to get the cipher message 44,15,375,44,25

Decryption requires a key and a numeric text.

Example: The ciphered message is 44,15,375,44,25 and the key 11,5,25 (for KEY)

Divide the first number of the message by the second number of the key. Write the result (which must be integer). Same for the next numbers of the message and the key.

Example: 44/11=4, 15/5=3 etc.

Example: The original plain text is 4,3,15,4,5 (DCODE).

The message is made of numbers with 1 to 5 digits, none is prime.

Vigenere multiplication can be cracked by trying to find the length for which GCD of values are the greatest.