Hashtable查找

Question

下面的代码创建一个包含反向密码的哈希表。我正在尝试对哈希表预先形成一个查找，并返回结果。我正在尝试解密提供给我的XML文件中的内容，下面是我在powershell中创建的脚本。

$translation = [ordered]@{}
$alpha = 'A'..'Z'
For($i=0; $i -lt 26; $i++)
{
 $translation[$alpha[((((-$i + $offset) % 26) + 26) % 26)]] = $alpha[$i]
}

XML文件包含：

<?xml version="1.0" encoding="UTF-8"?>
<translate>
  <caesar_cipher>
    <offset>-7</offset>
    <cipher>
RFGNCTAZITALFGB FG BZRRPBBOZIIV RFHEIPALGN AMP TQYTGRPQ EFXPCBMPII 
TBBLNGHPGA
    </cipher>
  </caesar_cipher>
</translate>

您知道如何在哈希表中预先形成一个查找来解密XML文件中的消息，然后输出到powershell吗？

Answer 1

# The input XML.
$xml = @'
<?xml version="1.0" encoding="UTF-8"?>
<translate>
  <caesar_cipher>
    <offset>-7</offset>
    <cipher>
RFGNCTAZITALFGB FG BZRRPBBOZIIV RFHEIPALGN AMP TQYTGRPQ EFXPCBMPII 
TBBLNGHPGA
    </cipher>
  </caesar_cipher>
</translate>
'@

# Read the XML text into an XML DOM (XmlDocument).
$doc = [xml] $xml

# Extract the offset needed to build the translation hashtable.
$offset = $doc.translate.caesar_cipher.offset

# Build the translation hashtable, which maps a given [char] instance
# to a different [char] instance.
# (The hashtable doesn't strictly need to be *ordered*.)
$translation = [ordered] @{}
# NOTE: 'A'..'Z' only works in PowerShell *Core*.
#       In *Windows PowerShell* you must use construct the array via *code points*, 
#       as shown in the next statement.
$alpha = [char[]] (65..90)
for($i=0; $i -lt 26; $i++) {
  $translation[$alpha[((((-$i + $offset) % 26) + 26) % 26)]] = $alpha[$i]
}
# Add an entry to pass spaces through as-is.
$translation[[char] ' '] = [char] ' '

# Extract the text to be deciphered.
$cipherText = $doc.translate.caesar_cipher.cipher

# Translate the individual characters and reassemble them into a string.
-join $translation[[char[]] $cipherText]

上述收益率：

CONGRATULATIONS ON SUCCESSFULLY COMPLETING THE ADVANCED POWERSHELL ASSIGNMENT    

并祝贺你成功地让我们为你做家庭作业。

注意：

• PowerShell自动提供方便的点表示法 to ，向下钻取到XML 。

- For background information and caveats, see [this answer](https://stackoverflow.com/a/49213568/45375).
- If you need sophisticated _queries_ agains the XML DOM, use the [`Select-Xml` cmdlet](https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.utility/select-xml), which is [XPath](http://en.wikipedia.org/wiki/XPath)-based.

​

• Pitfall：PowerShell通常会根据需要自动将[char]实例视为[string]实例，但在哈希表查找的情况下则不会：哈希表查找必须使用与键的数据类型相同的数据类型，这就是为什么$cipherText被转换为[char[]]来查找[char]实例，以及为什么为上面的空格添加条目使用显式[char]强制转换来定义键。
• Windows PowerShell只支持范围运算符..的数字端点，而PowerShell Core也支持字符。

Answer 2

你的剧本有几个问题。首先，你这一代的密码数学是错误的。您想要从xml中提取偏移量。您还希望捕获散列中的空格字符，否则在执行查找时它将返回$null。这对于任何其他非alpha字符都是正确的，除非您已经定义了它们。一旦解决了这个问题，您所需要做的就是执行查找，并将字符重新组合在一起。您可以在字典中执行多个查找，方法是在PowerShell中传递一个数组，如下所示。

# initialize alpha and hash lookups
$alpha = 'A'..'Z'
$decipher = @{ ' ' = ' ' }

# load prerequisite variables
$xml = [xml]@'
<?xml version="1.0" encoding="UTF-8"?>
<translate>
  <caesar_cipher>
    <offset>-7</offset>
    <cipher>
RFGNCTAZITALFGB FG BZRRPBBOZIIV RFHEIPALGN AMP TQYTGRPQ EFXPCBMPII TBBLNGHPGA
    </cipher>
  </caesar_cipher>
</translate>
'@
$offset = [int]$xml.translate.caesar_cipher.offset
$cipher = $xml.translate.caesar_cipher.cipher

# generate decipher table
0..($alpha.Length - 1) | % {$decipher["$($alpha[(-$_ + $offset) % $alpha.Length])"] = $alpha[$_]}

# perform lookups
-join $decipher[$cipher -split '']

Answer 3

正如TheIncorrigible1所建议的，您可以使用XPath表达式//cipher/text()来选择所需的文本节点。

$xml = [xml](Get-Content path\to\file.xml)

$Ciphers = $xml.SelectNodes('//cipher/text()').InnerText
foreach($Cipher in $Ciphers){
  Write-Host "Cipher text:`n$Cipher" -ForegroundColor Magenta
  Write-Host "Decrypted text:`n$(-join ($Cipher.ToCharArray() |ForEach-Object {
    # if it's in the set A..Z, translate
    if($_ -in $alpha){
      $_ = $translation[$_]
    }
    $_
  }))" -ForegroundColor Green
}