1643.sagews

cipher = "OHNCCIBEDDYKXWFFDYIEGHFFCDODYFIQRXDXDMHWBWFDBPGXEDWYSINXTRFIYIQTBFNDXFIWYQTFCDSXDIFDBFSDYWHBDBWYFCWBIXFIBWYDJDXTGFCDXRGBBDBBIMHIQWFTGPWYFDQQDNFFCIFUDPWDBUDPWYWFWGYIYUOTBFWPWDBOGXDIJDXISDOWYUBEHFFCGHSCQDBBDXBGHQBNIYYGFCGRDFGDMHIQEDDFCGJDYGXOWNCDQIYSDQGFCDTYDDUYGFFCDXDPGXDUDNQWYDFGKCWBFQDFCDQIFDBFFHYDGXFGFGHNCIRDYNWQFCDDIXYDBFBFHUDYFWBNIRIEQDGPQDIXYWYSFCDXHQDBIYUIBIYIOIFDHXGPDYZGTWYSCWBINCWDJDODYF"

len(cipher)

398

key = dict()

for i in range(26):
    key[chr(ord('A')+i)]= chr(ord('A')+i)

sage: def apply_key(cipher_text,cipher_key):
...       plain_text = ""
...       for ch in cipher_text:
...           plain_text += cipher_key[ch]
...       return plain_text

sage: def list_cmp(x,y):
...       if x[1]<y[1]:
...           return int(1)
...       if x[1]>y[1]:
...           return int(-1)
...       return int(0)

sage: #Based on most common letter
sage: key['D'] = 'e'
sage: #Based on most common digraph
sage: key['C'] = 'h'
sage: key['F'] = 't'
sage: #Based on most common digraph not containing eth
sage: key['W'] = 'i'
sage: key['Y'] = 'n'
sage: #Based on most common remaining letter
sage: key['I'] = 'a'
sage: #Based on common letter with lots of doubles occurances
sage: key['B'] = 's'
sage: #To make the work "been" after has
sage: key['E'] = 'b'
sage: #To make ab__t into about
sage: key['G'] = 'o'
sage: key['H'] = 'u'
sage: #Based on frequency and high digraph of Qe
sage: key['X'] = 'r'
sage: #Based on the Mu digraph frequency
sage: key['M'] = 'q'
sage: #To make _ritten into written
sage: key['K'] = 'w'
sage: #To make _rerequisites into prerequisites
sage: key['R'] = 'p'
sage: #To make _u_h into much
sage: key['O'] = 'm'
sage: key['N'] = 'c'
sage: #To make _ental into mental
sage: key['Q'] = 'l'
sage: #To make cr_ptanal_st into cryptanalyst
sage: key['T'] = 'y'
sage: #To make _or into for
sage: key['P'] = 'f'
sage: #To make bein_ into being
sage: key['S'] = 'g'
sage: #To make e_ery into every
sage: key['J'] = 'v'
sage: #To make _efies_efinition into defies definition
sage: key['U'] = 'd'
sage: #To make en_oy into enjoy
sage: key['Z'] = 'j'

sage: data = [["Letter", "Frequency", "Percentage"]]
sage: for i in range(26):
...       data.append([key[chr(ord('A') + i)],cipher.count(chr(ord('A') + i)),100*(0.0+cipher.count(chr(ord('A') + i)))/len(cipher) ])
...
sage: data.sort(list_cmp)
sage: html.table(data)

Letter	Frequency	Percentage
e	63	15.8291457286432
t	45	11.3065326633166
n	32	8.04020100502512
a	31	7.78894472361809
s	29	7.28643216080402
i	27	6.78391959798995
o	24	6.03015075376884
h	21	5.27638190954774
r	21	5.27638190954774
l	18	4.52261306532663
u	14	3.51758793969849
c	11	2.76381909547739
m	8	2.01005025125628
f	8	2.01005025125628
g	8	2.01005025125628
y	8	2.01005025125628
d	8	2.01005025125628
b	6	1.50753768844221
p	6	1.50753768844221
v	4	1.00502512562814
q	3	0.753768844221106
w	2	0.502512562814070
j	1	0.251256281407035
A	0	0.000000000000000
L	0	0.000000000000000
V	0	0.000000000000000

sage: data = list(range(27))
sage: for i in range(27):
...       data[i] = list(range(27))
...
sage: for i in range(26):
...       data[0][1+i] = key[chr(ord('A') + i)]   
...
sage: for i in range(26):
...       data[1+i][0] = key[chr(ord('A') + i)]  
...

sage: for i in range(26):
...       f = chr(ord('A') + i)
...       for j in range(26):
...           s = chr(ord('A') + j)
...           if cipher.count(f+s) == 0:
...               data[i+1][j+1] = " "
...           else:
...               data[i+1][j+1] = cipher.count(f+s)
...           
...
sage: html.table(data)

0	A	s	h	e	b	t	o	u	a	v	w	L	q	c	m	f	l	p	g	y	d	V	i	r	n	j
A
s		3		3	2	7	1		5					2	1	1					1		3
h			1	9			3		3								1						4
e		10		4		4	2	1	4	2			2	2	3	3	4		1	1	2		1	8	9
b				3			1	1									1
t		1	13	6		6	4	2	4					1			1		1	1	1		3
o		1		1		5		4		1	1					3		1		1				5	1
u		1				2			2					2			2		1		1		1	1	1
a		3			2	4				1			1	2	1		4	2	1				1	3	6
v				4
w			1																					1
L
q								3
c			4	1		1			2								1						1	1
m				2			1	1	1											1			2
f				1			2										1						4
l		1		6	1	1	1		2								1	1		2			2
p				2		1	1		1															1
g			2	3		1			1															1
y		2				1	2											1					1		1
d		1		4					1						1										1
V
i		5		3		4	1	1						1		1	1								10
r		1		6	1	3	1	1	1						1			1		2			1		2
n				5		5	3		4		1			1			1		4		3		3		1	1
j							1

sage: apply_key(cipher,key)

'muchhasbeenwrittenaboutthementalprerequisitesforbeingacryptanalystcertainlythegreatestgeniusesinthisartasineveryotherpossessaqualityofintellectthatdefiesdefinitionandmystifiesmoreaveragemindsbutthoughlessersoulscannothopetoequalbeethovenormichelangelotheyneednotthereforedeclinetowhistlethelatesttuneortotouchapenciltheearneststudentiscapableoflearningtherulesandasanamateurofenjoyinghisachievement'