a1.cipher

GOXJPTMFMFTRGUICNGYGUFUIBGYNCN
FUXJPTMFMFTRGUICNFZBTGUCFECJOC
NFOGMYCTYYGIUQFUCGUJPMLMXZCJIM
TZNXLJPMYFCNGYTYYGIUQFUCWTYYPZ
ZJYFRBXZJYCFRCWJRTXYHFOJMFCNFF
URJOCNFFGINCNQJUCNGUCNFXFTMJOC
WFUCXOJPMCFFUTYXJPNTSFRGYLJSFM
FRHXLMTLVGUICNGYTYYGIUQFUCGCWT
YFULMXZCFRPYGUITYGQZBFQJUJTBZN
THFCGLYPHYCGCPCGJULGZNFMOJMCNG
YTYYGIUQFUCYPHQGCCNFOJBBJWGUIG
CFQYHXFQTGBTCBFTYCHFOJMFCNFCNG
MRWFFVJOCNFOJBBJWGUIQJUCNOGMYC
ZMJSGRFCNFYPHYCGCPCGJUCTHBFPYF
ROJMCNFBFCCFMYZMFYFUCGUCNFZBTG
UCFECYFLJURRFYLMGHFNJWXJPHMJVF
CNGYLGZNFMCNGMRRFYLMGHFTURGQZB
FQFUCXJPMJWULGZNFMYXYCFQOJMFUL
MXZCGUITURRFLMXZCGUICFECOGBFYX
JPQTXPYFTUXZMJIMTQQGUIBTUIPTIF
JOXJPMLNJGLFTYZTMCJOCNFYPHQGYY
GJUOJMCNFCNGMRZTMCZMJSGRFTBGSF
RFQJUYCMTCGJUJOXJPMYXYCFQOJPMC
NWMGCFTYNJMCMFZJMCJUCNFYCTCGYC
GLTBBFCCFMOMFDPFULGFYJOFUIBGYN
GULJQZTMGYJUWGCNJCNFMBTUIPTIFY
RFCFMQGUFGOFUIBGYNGYLJUYGRFMFR
CNFBFTYCMTURJQJOQJYCUTCPMTBBTU
IPTIFY

count.py

#!/usr/bin/env python3

import sys
from collections import defaultdict
from itertools import tee

english = "etaoinshrdlcumwfgypbvkjxqz"

ciphertext = open('a1.cipher').read()
cleartext = ciphertext
ciphertext = ciphertext.replace('\n', '')

ln = len(ciphertext)

d = defaultdict(int)

for c in ciphertext:
    d[c] += 1

print("single letter freqs\n")

sed = []

for i,(k,v) in enumerate(sorted(d.items(), key=lambda vs: vs[1], reverse=True)):
    per = v / ln
    probs = english[i]
    sed.append("s/{}/{}/g".format(k, probs))
    print("{}: {:2f}% (probs {})".format(k, per, probs))
    cleartext = cleartext.replace(k, probs)

print("\n\ndouble letter freqs\n")

# straight from itertools
def pairwise(iterable):
    a, b = tee(iterable)
    next(b, None)
    return zip(a, b)

d = defaultdict(int)

for cc in pairwise(ciphertext):
    d[cc] += 1

doubs = []

for k,v in sorted(d.items(), key=lambda vs: vs[1], reverse=True):
    doub = k[0] + k[1]
    per = v / ln
    if k[0] == k[1]:
        doubs.append(k, per)
    if per < 0.02:
        break
    print("{}: {:2%}%".format(k, per))

if doubs:
    print("\n\nidentical doubles:")
    for doub in doubs:
        print("{}: {:2%}%".format(doub[0], doub[1]))

print("\nI think it's:")
print(cleartext)

print("\nsed script:")
for s in sed:
    print(s)