简单替代密码
简单替换密码是最常用的密码，包括为每个密文文本字符替换每个纯文本字符的算法.在这个过程中，与凯撒密码算法相比，字母表是混乱的.
示例
简单替换密码的密钥通常由26个字母组成.一个示例键是 :
plain?alphabet?:?abcdefghijklmnopqrstuvwxyz cipher?alphabet:?phqgiumeaylnofdxjkrcvstzwb
使用上述密钥的示例加密是 :
plaintext?:?defend?the?east?wall?of?the?castle ciphertext:?giuifg?cei?iprc?tpnn?du?cei?qprcni
以下代码显示了一个实现简单替换密码的程序;
import?random,?sys
LETTERS?=?'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
def?main():
???message?=?''
???if?len(sys.argv)?>?1:
??????with?open(sys.argv[1],?'r')?as?f:
?????????message?=?f.read()
???else:
??????message?=?raw_input("Enter?your?message:?")
???mode?=?raw_input("E?for?Encrypt,?D?for?Decrypt:?")
???key?=?''
???
???while?checkKey(key)?is?False:
??????key?=?raw_input("Enter?26?ALPHA?key?(leave?blank?for?random?key):?")
??????if?key?==?'':
?????????key?=?getRandomKey()
??????if?checkKey(key)?is?False:
print('There?is?an?error?in?the?key?or?symbol?set.')
???translated?=?translateMessage(message,?key,?mode)
???print('Using?key:?%s'?%?(key))
???
???if?len(sys.argv)?>?1:
??????fileOut?=?'enc.'?+?sys.argv[1]
??????with?open(fileOut,?'w')?as?f:
?????????f.write(translated)
??????print('Success!?File?written?to:?%s'?%?(fileOut))
???else:?print('Result:?'?+?translated)
#?Store?the?key?into?list,?sort?it,?convert?back,?compare?to?alphabet.
def?checkKey(key):
???keyString?=?''.join(sorted(list(key)))
???return?keyString?==?LETTERS
def?translateMessage(message,?key,?mode):
???translated?=?''
???charsA?=?LETTERS
???charsB?=?key
???
???#?If?decrypt?mode?is?detected,?swap?A?and?B
???if?mode?==?'D':
??????charsA,?charsB?=?charsB,?charsA
???for?symbol?in?message:
??????if?symbol.upper()?in?charsA:
?????????symIndex?=?charsA.find(symbol.upper())
?????????if?symbol.isupper():
????????????translated?+=?charsB[symIndex].upper()
?????????else:
????????????translated?+=?charsB[symIndex].lower()
else:
???????????????translated?+=?symbol
?????????return?translated
def?getRandomKey():
???randomList?=?list(LETTERS)
???random.shuffle(randomList)
???return?''.join(randomList)
if?__name__?==?'__main__':
???main()
输出
您可以观察以下内容当你实现上面给出的代码时输出 :
简单替换密码测试
我们将重点介绍如何使用各种方法测试替换密码，这有助于生成随机字符串，如下面所示 :
import?random,?string,?substitution
def?main():
???for?i?in?range(1000):
??????key?=?substitution.getRandomKey()
??????message?=?random_string()
??????print('Test?%s:?String:?"%s.."'?%?(i?+?1,?message[:50]))
??????print("Key:?"?+?key)
??????encrypted?=?substitution.translateMessage(message,?key,?'E')
??????decrypted?=?substitution.translateMessage(encrypted,?key,?'D')
??????
??????if?decrypted?!=?message:
?????????print('ERROR:?Decrypted:?"%s"?Key:?%s'?%?(decrypted,?key))
?????????sys.exit()
??????print('Substutition?test?passed!')
def?random_string(size?=?5000,?chars?=?string.ascii_letters?+?string.digits):
???return?''.join(random.choice(chars)?for?_?in?range(size))
if?__name__?==?'__main__':
???main()
输出
您可以随机观察输出生成的字符串有助于生成随机纯文本消息，如下所示 :
测试成功完成后，我们可以观察输出消息替换测试通过！.
因此，您可以系统地破解替换密码.
简单替换密码解密
您可以了解替换密码的简单实现，它根据简单替换密码技术中使用的逻辑显示加密和解密的消息.这可以被视为一种替代编码方法.
代码
您可以使用以下代码使用简单替换密码来执行解密;
import?random
chars?=?'ABCDEFGHIJKLMNOPQRSTUVWXYZ'?+????'abcdefghijklmnopqrstuvwxyz'?+????'0123456789'?+????':.;,?!@#$%&()+=-*/_<>?[]{}`~^"\'\\'
def?generate_key():
???"""Generate?an?key?for?our?cipher"""
???shuffled?=?sorted(chars,?key=lambda?k:?random.random())
???return?dict(zip(chars,?shuffled))
def?encrypt(key,?plaintext):
???"""Encrypt?the?string?and?return?the?ciphertext"""
???return?''.join(key[l]?for?l?in?plaintext)
def?decrypt(key,?ciphertext):
???"""Decrypt?the?string?and?return?the?plaintext"""
???flipped?=?{v:?k?for?k,?v?in?key.items()}
???return?''.join(flipped[l]?for?l?in?ciphertext)
def?show_result(plaintext):
???"""Generate?a?resulting?cipher?with?elements?shown"""
???key?=?generate_key()
???encrypted?=?encrypt(key,?plaintext)
???decrypted?=?decrypt(key,?encrypted)???
???print?'Key:?%s'?%?key
print?'Plaintext:?%s'?%?plaintext
???print?'Encrypted:?%s'?%?encrypted
???print?'Decrypted:?%s'?%?decrypted
show_result('Hello?World.?This?is?demo?of?substitution?cipher')
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