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week4_5_解密與破密.md

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破密分析

Crypto

替換式密碼Substitution cipher

換位加密法Transposition cipher

Scytale cipher密碼棒

Crypto_001_最愛凱薩

  • ABCTF 2016 : ceasar-salad-10 10

解法1:使用線上工具解題

輸入看看http://www.xarg.org/tools/caesar-cipher/

解法2:使用線上工具解題

暴力破解法[窮舉法] Brute Force
把所有可能的方法都執行看看

https://planetcalc.com/1434/

解法3:直覺法

xyzqc{t3_qelrdeq_t3_k33a3a_lk3_lc_qe3p3}==>abctf{FLAG}

解法4:使用python程式解題(作業參看其他解題)

Crypto_002_暴力破解法的奧義

angstromCTF 2017:The Beginning

其他練習

  • EasyCTF 2015: Julius Save Me (20)

https://github.com/ctfs/write-ups-2015/tree/master/easyctf-2015/cryptography/julius-save-me

Crypto_003_頻率分析法

Crypto_004_頻率分析法續集

Crypto_005_頻率分析法第三集

  • angstromCTF 2017: Substitution Cipher 60
  •  

Crypto_006_密碼棒加密法

  • EKOPARTY CTF 2015: SCYTCRYPTO 50

解法一:

解題步驟1:

題目告訴你SCYTCrypto+又是密碼問題===>要想得到scytale-cipher

解題步驟2:善用Google看看

www.dcode.fr/scytale-cipher

解題步驟3:使用線上工具 http://www.dcode.fr/scytale-cipher

解法二:使用linux 指令fold

Usage: fold [OPTION]... [FILE]...
Wrap input lines in each FILE, writing to standard output.

With no FILE, or when FILE is -, read standard input.

Mandatory arguments to long options are mandatory for short options too.
  -b, --bytes         count bytes rather than columns
  -s, --spaces        break at spaces
  -w, --width=WIDTH   use WIDTH columns instead of 80
  --help     display this help and exit
  --version  output version information and exit

Crypto_007_Bacon cipher

暫未出題

angstromCTF 2016 : shakespeare-60

intext = "tOBeoRNottOBeTHATiStHeQueSTIONWHetHErTISnOBlERINTHeMInDtOSuffERThESlINGSaNDaRRowSOFoUTRAGEoUSFoRtuNeORTOTAkeARMSaGAINStaSEAofTRoUBlESANDbYOPpOSInGEnDTHEM"
outtext = ""
for c in intext:
    if c.isupper():
            outtext += "B"
    else:
            outtext += "A"

print outtext
'ABBAABBAAABBABBBBABABABAABBBBBBBAABBABBBABBABBBBBBABBABABBAAABBBABBABBBBABBABBAABBBABBBBBBABBBABAABABBBBBBAABBBBABBBBBAABBBAABBABBABBBBBABBBABBBABBABBBBB'

Crypto_101_凱薩密碼擴充版

import string

caesaralpha = "abcdefghijklmnopqrstuvwxyz0123456789"

def caesar(input_string, rot):
    output_string = ""
    for i in range(len(input_string)):
        if input_string[i].isalnum():
            idx = (caesaralpha.find(input_string[i]) + rot) % len(caesaralpha)
            output_string += caesaralpha[idx]
        else:
            output_string += input_string[i]
    return output_string

enc = '7sj-ighm-742q3w4t' # encrypt data

for i in range(len(caesaralpha)):
    print caesar(enc, i)

Transposition cipher

https://en.wikipedia.org/wiki/Transposition_cipher

Crypto_102_Transposition cipher

解題步驟1:

file fore1.core

解題步驟2:

$ strings fore1.core

….
cvqAeqacLtqazEigwiXobxrCrtuiTzahfFreqc{bnjrKwgk83kgd43j85ePgb_e_rwqr7fvbmHjklo3tews_hmkogooyf0vbnk0ii87Drfgh_n kiwutfb0ghk9ro987k5tfb_hjiouo087ptfcv}
….

解題步驟3:使用python解題

sol

cipher='cvqAeqacLtqazEigwiXobxrCrtuiTzahfFreqc{bnjrKwgk83kgd43j85ePgb_e_rwqr7fvbmHjklo3tews_hmkogooyf0vbnk0ii87Drfgh_n kiwutfb0ghk9ro987k5tfb_hjiouo087ptfcv}'

cipher=cipher[3:]
flag = ''
for x in range(0,len(cipher),1):
    if x%5==0:
        flag+=cipher[x]
print flag


cipher='cvqAeqacLtqazEigwiXobxrCrtuiTzahfFreqc{bnjrKwgk83kgd43j85ePgb_e_rwqr7fvbmHjklo3tews_hmkogooyf0vbnk0ii87Drfgh_n kiwutfb0ghk9ro987k5tfb_hjiouo087ptfcv}'

''.join(cipher[3 : : 5])

s = 'cvqAeqacLtqazEigwiXobxrCrtuiTzahfFreqc{bnjrKwgk83kgd43j85ePgb_e_rwqr7fvbmHjklo3tews_hmkogooyf0vbnk0ii87Drfgh_n kiwutfb0ghk9ro987k5tfb_hjiouo087ptfcv}'
print s[3::5]

python sol.py

Crypto_103_affine-cipher

解題:使用python程式解題

import string

s = string.ascii_lowercase # a-z
s += '_'
d = {}
for c in range(len(s)):
	d[s[(c*4 + 15)%27]] = s[c]
ciphertext = 'ifpmluglesecdlqp_rclfrseljpkq'
s1 = ''
for x in cr:
	s1 += d[x]
print s1