Beaufort Cipher (encoder / decoder) Examples

1. Beaufort Cipher encoder

Text : ABCD efghi
Key : bcd
Alphabet : abcdefghijklmnopqrstuvwxyz
Mode : Key-Text

Solution:

The Beaufort cipher is a polyalphabetic substitution cipher, where the plaintext is subtracted from the keyword to encrypt a message

Alphabet = abcdefghijklmnopqrstuvwxyz

Letter	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
Number	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25

Plaintext	A	B	C	D	e	f	g	h	i
Plaintext Value (2)	0	1	2	3	4	5	6	7	8
Key	b	c	d	b	c	d	b	c	d
Key Value (4)	1	2	3	1	2	3	1	2	3
Key Value - Plaintext Value (4) - (2) Mod 26	1	1	1	-2+26 =24	-2+26 =24	-2+26 =24	-5+26 =21	-5+26 =21	-5+26 =21
Ciphertext	B	B	B	Y	y	y	v	v	v

2. Beaufort Cipher encoder

Text : hello world
Key : bcd
Alphabet : abcdefghijklmnopqrstuvwxyz
Mode : Key-Text

Solution:

The Beaufort cipher is a polyalphabetic substitution cipher, where the plaintext is subtracted from the keyword to encrypt a message

Alphabet = abcdefghijklmnopqrstuvwxyz

Letter	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
Number	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25

Plaintext	h	e	l	l	o	w	o	r	l	d
Plaintext Value (2)	7	4	11	11	14	22	14	17	11	3
Key	b	c	d	b	c	d	b	c	d	b
Key Value (4)	1	2	3	1	2	3	1	2	3	1
Key Value - Plaintext Value (4) - (2) Mod 26	-6+26 =20	-2+26 =24	-8+26 =18	-10+26 =16	-12+26 =14	-19+26 =7	-13+26 =13	-15+26 =11	-8+26 =18	-2+26 =24
Ciphertext	u	y	s	q	o	h	n	l	s	y

This material is intended as a summary. Use your textbook for detail explanation.
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