Method

Suppose we have a keyword EMAIL.

EMAIL --> AEILM

Calculate position of each letter in original keyword. So A is in position $3$ and thus $3$ is the first digit

A -> 3
E -> 1
I -> 4
L -> 5
M -> 2

If we want to encrypt

MEET ME AT NOON

Then since len("EMAIL") = 5, we encode this as

MEETM
EATNO
ONQXJ

where QXJis junk to fill the last line. This is then encrypted as

EMTME
TENOA
QOXJN

by using $31452$ . It tells us to use

giving us the ciphertext

EMTMETENOAQOXJN

Examples

Keyword: Zeus
Plaintext: MTSQAGXY

ZEUS -> ESUZ -> 2431

MTSQ -> TQSM
AGXY -> GYXA

Corresponding Ciphertext: TQSMGYXA (B)