Interrupted Key Cipher solver calculator (encoder / decoder)

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Solution (Print / Save)

Solution provided by AtoZmath.com

1. ABCD efghi

2. hello world

Example (with steps)

1. Interrupted Key Cipher encoder

Text : ABCD efghi
Substitution Cipher Method : vigenere
Key : start
Alphabet : abcdefghijklmnopqrstuvwxyz
Interrupt by (Word / Random) : Word Interrupt

Solution:

The Interrupted Key cipher is a Periodic substitution cipher that uses a keyword which is paused and restarted at each word or at random intervals, making it more secure. It can be used with any of the Periodic Substitution Cipher: Vigenere, Beaufort, Variant Beaufort, Porta Cipher.

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

Each letter is shifted down based on the key letter

Plaintext	A	B	C	D	e	f	g	h	i
Text Value (2)	0	1	2	3	4	5	6	7	8
Key (repeated)	s	t	a	r	s	t	a	r	t
Key Value (4)	18	19	0	17	18	19	0	17	19
Addition (2) + (4) Mod 26	18	20	2	20	22	24	6	24	27=1
Ciphertext	S	U	C	U	w	y	g	y	b

So finally

Plaintext	: ABCD efghi
Key	: start
Ciphertext	: SUCU wygyb

2. Interrupted Key Cipher encoder

Text : hello world
Substitution Cipher Method : vigenere
Key : start
Alphabet : abcdefghijklmnopqrstuvwxyz
Interrupt by (Word / Random) : Word Interrupt

Solution:

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

Each letter is shifted down based on the key letter

Plaintext	h	e	l	l	o	w	o	r	l	d
Text Value (2)	7	4	11	11	14	22	14	17	11	3
Key (repeated)	s	t	a	r	t	s	t	a	r	t
Key Value (4)	18	19	0	17	19	18	19	0	17	19
Addition (2) + (4) Mod 26	25	23	11	28=2	33=7	40=14	33=7	17	28=2	22
Ciphertext	z	x	l	c	h	o	h	r	c	w

So finally

Plaintext	: hello world
Key	: start
Ciphertext	: zxlch ohrcw