View source for AES256CBCdecrypt and AES256CBCencrypt (String functions)

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<var>AES256CBCdecrypt</var> and <var>AES256CBCencrypt</var> are synonyms for the [[String class]] function that applies the DEA (Data Encryption Algorithm) using a 256-bit symmetric key to decrypt or encrypt each 128-bit block of input text. CBC (Cipher Block Chaining) refers to a randomizing tactic whereby the result of applying the AES cipher to a 128-bit block is combined with the next block before the next block's encryption; and so on for each subsequent block. An initialization vector is used in the first block to make its encryption unique.

For more details about how the algorithm works, see [https://en.wikipedia.org/wiki/Data_Encryption_Standard Data Encryption Standard] and [https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Cipher Block Chaining (CBC) Cipher Block Chaining (CBC)].

The length of the returned string is the same as that of the object string.

AES is a two-way cipher, so encrypting a string with a key and then decrypting the result of that encryption with the same key produces the original string. That is, the following assertion should <b><i>always</i></b> hold:
<p class="code">[[Assert statement|assert]] %string:aes256cbcencrypt(%key):aes256cbcdecrypt(%key) eq %string
</p>
You can use <var>AES256CBCdecrypt</var> to "document" that you are decrypting, and
use <var>AES256CBCencrypt</var> to "document" that you are encrypting. You can use <var>AES256CBCdecrypt</var> and <var>AES256CBCencrypt</var> interchangeably on the rest of this page.

==Syntax==
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{{Template:String:AES256CBCencrypt syntax}}

===Syntax terms===
<table>
<tr><th>%outString</th>
<td>A string variable to receive the encrypted or decrypted method object <var class="term">string</var>. Its length is the same as <var class="term">string</var>.</td></tr>

<tr><th>string</th>
<td>The string to which the method is applied. <var class="term">string</var> must be a multiple of sixteen bytes in length; its  maximum is 32768 bytes. It may be null.</td></tr>

<tr><th>key</th>
<td>A 32-byte (only) string variable whose value is used to encrypt or decrypt the method object, <var class="term">string</var>.</td></tr>

<tr><th>initVector</th>
<td>A 16-byte string that is used to randomize the encryption.
The initialization vector is used to ensure distinct ciphertexts are produced even when the same plaintext is encrypted multiple times independently with the same key.</td></tr>
</table>

==Usage notes==
<ul>
<li>You are <b><i>not</i></b> prevented from creating confusion by encrypting with <var>AES256CBCdecrypt</var> and decrypting with <var>AES256CBCencrypt</var>. </li>

<li>The <var>AES256CBCdecrypt</var> and <var>AES256CBCencrypt</var> functions are available as of <var class="product">Model&nbsp;204</var> 7.6. </li>
</ul>

==Examples==
In the following example, the output string from the <var>AES256CBCencrypt</var> method is converted to hex using the <var>[[StringToHex (String function)|StringToHex]]</var> function to reveal its non-displayable characters, then decrypted to return the original input string:

<p class="code">b                    
%ls is longstring    
%string is longstring
%key is string len 32
%iv is string len 16
%string = 'onetwothreefour0onetwothreefour0'
%key = '12345678161616162424242432323232'
%iv = 'abcdefgh16161616'

%ls = %string:aes256cbcencrypt(%key, %iv)
[[PrintText statement|printText]] {~} is {%ls:stringTohex}
printText {~} is: {%ls:aes256cbcdecrypt(%key, %iv)}
end
</p>
The result is:
<p class="output">%ls:stringTohex is: BD9E29B6AE9F796AECEDFC69ACBF0030AB4CFED68139EB6518262C648D133DF3
%ls:aes256cbcdecrypt(%key, %iv) is: onetwothreefour0onetwothreefour0
</p>

==See also==
<ul>
<li>Additional AES methods:
<ul>
{{Template:AES crypto methods}}
</ul></li>

<li>Additional two-way ciphers: 
<ul>
{{Template:DEA crypto methods}}
<li>[[RC4decrypt and RC4encrypt (String functions)]]</li>
</ul></li>

<li><var>String</var> hashes: 
<ul>
{{Template:Digest methods}} 
</ul></li>
</ul>

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