caesar_cipher 凯撒密码

caesar_cipher 凯撒密码

概念

凯撒密码是一种简单的替代密码，根据苏维托尼乌斯的记载，凯撒密码是由罗马共和国独裁官盖乌斯·尤利乌斯·恺撒发明的，他曾用凯撒密码来加密重要的军事情报。

作为一种替代加密算法，凯撒密码在如今看来，并非那么安全，它的加密方式只是简单的移位和替换，例如，如果明文移位1，则A被B替代，B将变为C，依此类推。

如果知道偏移位密钥，对密文解密是很简单的，只需用移位密钥表替换回正常字母表字母即可
移位密钥表的规律很简单，不管偏移几位数，这些字母都移动到正常字母表的最后。

如果不知道偏移位数密钥，怎么解密密文呢，方式其实也并不困难，因为凯撒密码只有25种偏移位数的可能性，所以，只需要计算出这25种结果，必然有一种结果是明文。

算法

• encrypt 加密

def encrypt(input_string: str, key: int, alphabet: Optional[str] = None) -> str:
    """
    encrypt
    =======
    Encodes a given string with the caesar cipher and returns the encoded
    message

    Parameters:
    -----------
    *   input_string: the plain-text that needs to be encoded
    *   key: the number of letters to shift the message by

    Optional:
    *   alphabet (None): the alphabet used to encode the cipher, if not
        specified, the standard english alphabet with upper and lowercase
        letters is used

    Returns:
    *   A string containing the encoded cipher-text

• decrypt 解密

def decrypt(input_string: str, key: int, alphabet: Optional[str] = None) -> str:

• brute_force 暴力破解

def brute_force(input_string: str, alphabet: Optional[str] = None) -> Dict[int, str]:
    """
    brute_force
    ===========
    Returns all the possible combinations of keys and the decoded strings in the
    form of a dictionary

    Parameters:
    -----------
    *   input_string: the cipher-text that needs to be used during brute-force

    Optional:
    *   alphabet:  (None): the alphabet used to decode the cipher, if not
        specified, the standard english alphabet with upper and lowercase
        letters is used

代码

[caesar_cipher.py]{..\src\ciphers\caesar_cipher.py}

"""
Prepare
   1. sys.path 中增加 TheAlgorithms\src 子模块

"""
import sys
sys.path.append('E:\dev\AI\TheAlgorithms\src')

案例一：

encrypt 加密

from ciphers.caesar_cipher import encrypt,decrypt,brute_force
"""
    
"""

'''
encrypt('The quick brown fox jumps over the lazy dog', 8)
    'bpm yCqks jzwEv nwF rCuxA wDmz Bpm tiHG lwo'
'''
input_string = 'The quick brown fox jumps over the lazy dog'
key= 8+52
result = encrypt(input_string,key)

print(f'input_string:{input_string}' )
print(f'key：{key}' )
print(f'encrypt result:{result}' )
'''
encrypt('A very large key', 8000)
's nWjq dSjYW cWq'
'''

input_string = 'A very large key'
key= 8000
result = encrypt(input_string,key)

print(f'input_string:{input_string}' )
print(f'key：{key}' )
print(f'encrypt result:{result}' )

'''
encrypt('a lowercase alphabet', 5, 'abcdefghijklmnopqrstuvwxyz')
    'f qtbjwhfxj fqumfgjy'
'''

input_string = 'a lowercase alphabet'
key= 5
alphabet ='abcdefghijklmnopqrstuvwxyz'
result = encrypt(input_string,key,alphabet)
print(f'input_string:{input_string}' )
print(f'key：{key}' )
print(f'encrypt result:{result}' )

input_string:The quick brown fox jumps over the lazy dog
key：60
encrypt result:bpm yCqks jzwEv nwF rCuxA wDmz Bpm tiHG lwo
input_string:A very large key
key：8000
encrypt result:s nWjq dSjYW cWq
input_string:a lowercase alphabet
key：5
encrypt result:f qtbjwhfxj fqumfgjy

案例二：

decrypt 解密

from ciphers.caesar_cipher import encrypt,decrypt,brute_force
"""
    
"""
'''
>>> decrypt('bpm yCqks jzwEv nwF rCuxA wDmz Bpm tiHG lwo', 8)
    'The quick brown fox jumps over the lazy dog'
>>> decrypt('s nWjq dSjYW cWq', 8000)
    'A very large key'
>>> decrypt('f qtbjwhfxj fqumfgjy', 5, 'abcdefghijklmnopqrstuvwxyz')
    'a lowercase alphabet'
'''

print(decrypt('bpm yCqks jzwEv nwF rCuxA wDmz Bpm tiHG lwo', 8))
print(decrypt('s nWjq dSjYW cWq', 8000))
print(decrypt('f qtbjwhfxj fqumfgjy', 5, 'abcdefghijklmnopqrstuvwxyz'))

The quick brown fox jumps over the lazy dog
A very large key
a lowercase alphabet

案例三：

brute_force 暴力破解

brute_force(input_string: str, alphabet: Optional[str] = None) -> Dict[int, str]:

from ciphers.caesar_cipher import encrypt,decrypt,brute_force
"""
"""
'''
>>> brute_force("jFyuMy xIH'N vLONy zILwy Gy!")[20]
    "Please don't brute force me!"
'''
s = brute_force("jFyuMy xIH'N vLONy zILwy Gy!")
print(type(s))
print(s)
print(s[20])

<class 'dict'>
{1: "iExtLx wHG'M uKNMx yHKvx Fx!", 2: "hDwsKw vGF'L tJMLw xGJuw Ew!", 3: "gCvrJv uFE'K sILKv wFItv Dv!", 4: "fBuqIu tED'J rHKJu vEHsu Cu!", 5: "eAtpHt sDC'I qGJIt uDGrt Bt!", 6: "dzsoGs rCB'H pFIHs tCFqs As!", 7: "cyrnFr qBA'G oEHGr sBEpr zr!", 8: "bxqmEq pAz'F nDGFq rADoq yq!", 9: "awplDp ozy'E mCFEp qzCnp xp!", 10: "ZvokCo nyx'D lBEDo pyBmo wo!", 11: "YunjBn mxw'C kADCn oxAln vn!", 12: "XtmiAm lwv'B jzCBm nwzkm um!", 13: "Wslhzl kvu'A iyBAl mvyjl tl!", 14: "Vrkgyk jut'z hxAzk luxik sk!", 15: "Uqjfxj its'y gwzyj ktwhj rj!", 16: "Tpiewi hsr'x fvyxi jsvgi qi!", 17: "Sohdvh grq'w euxwh irufh ph!", 18: "Rngcug fqp'v dtwvg hqteg og!", 19: "Qmfbtf epo'u csvuf gpsdf nf!", 20: "Please don't brute force me!", 21: "OkdZrd cnm's aqtsd enqbd ld!", 22: "NjcYqc bml'r Zpsrc dmpac kc!", 23: "MibXpb alk'q Yorqb cloZb jb!", 24: "LhaWoa Zkj'p Xnqpa bknYa ia!", 25: "KgZVnZ Yji'o WmpoZ ajmXZ hZ!", 26: "JfYUmY Xih'n VlonY ZilWY gY!", 27: "IeXTlX Whg'm UknmX YhkVX fX!", 28: "HdWSkW Vgf'l TjmlW XgjUW eW!", 29: "GcVRjV Ufe'k SilkV WfiTV dV!", 30: "FbUQiU Ted'j RhkjU VehSU cU!", 31: "EaTPhT Sdc'i QgjiT UdgRT bT!", 32: "DZSOgS Rcb'h PfihS TcfQS aS!", 33: "CYRNfR Qba'g OehgR SbePR ZR!", 34: "BXQMeQ PaZ'f NdgfQ RadOQ YQ!", 35: "AWPLdP OZY'e McfeP QZcNP XP!", 36: "zVOKcO NYX'd LbedO PYbMO WO!", 37: "yUNJbN MXW'c KadcN OXaLN VN!", 38: "xTMIaM LWV'b JZcbM NWZKM UM!", 39: "wSLHZL KVU'a IYbaL MVYJL TL!", 40: "vRKGYK JUT'Z HXaZK LUXIK SK!", 41: "uQJFXJ ITS'Y GWZYJ KTWHJ RJ!", 42: "tPIEWI HSR'X FVYXI JSVGI QI!", 43: "sOHDVH GRQ'W EUXWH IRUFH PH!", 44: "rNGCUG FQP'V DTWVG HQTEG OG!", 45: "qMFBTF EPO'U CSVUF GPSDF NF!", 46: "pLEASE DON'T BRUTE FORCE ME!", 47: "oKDzRD CNM'S AQTSD ENQBD LD!", 48: "nJCyQC BML'R zPSRC DMPAC KC!", 49: "mIBxPB ALK'Q yORQB CLOzB JB!", 50: "lHAwOA zKJ'P xNQPA BKNyA IA!", 51: "kGzvNz yJI'O wMPOz AJMxz Hz!", 52: "jFyuMy xIH'N vLONy zILwy Gy!"}
Please don't brute force me!