iv         OCTET STRING DEFAULT 0,  -- Initialization vector
        keyLength  INTEGER                  -- Key length, in bits
    }

 注意：iv是可選的，默認為全0。在編碼后，如果使用全0的iv，那么該參數不
應該出現在參數中。解碼后，如果iv沒有出現在參數列表中，應該解釋為該參數全部
字節都是0。
下面是使用CAST-128對稱塊密碼算法的CBC模式的加密和解密。
cast5MAC OBJECT IDENTIFIER ::= { algorithms cast5MAC(11) }

    Parameters ::= SEQUENCE {
        macLength  INTEGER,       -- MAC length, in bits
        keyLength  INTEGER        -- Key length, in bits
    }
下面是使用CAST-128對稱塊密碼算法的消息驗證。

pbeWithMD5AndCast5CBC OBJECT IDENTIFIER ::=
    { algorithms pbeWithMD5AndCAST5-CBC(12) }

    Parameters ::= SEQUENCE {
        salt            OCTET STRING,
        iterationCount  INTEGER,      -- Total number of hash iterations
        keyLength       INTEGER       -- Key length, in bits
    }

    注意：IV是從哈希過程派生的，因此不必放在參數中。 
這是以CBC模式使用MD5和CAST-128對稱塊密碼的基于密碼的加密和解密。關于
PBE計算的詳細資料參見PKCS #5（它使用了DES密碼）。

2.7	討論
CAST-128是一種12或16循環的Feistel密碼，塊長度是64位，密碼長度最大128位；
它使用旋轉實現對線性和微分分析的內在免疫性；在循環函數中混合使用XOR、模為2**32
的加減法；在加密過程中使用三種不同的循環函數。最后，循環函數中使用的8x32置換箱，
每一個最小的非線性為74，而且不同的分配表中最大項是2。
按照其密碼長度（128）而言，這種加密是很強大的，而且具有很好的加密/解密效率，
在150MHz的奔騰處理器上每秒可以處理3.3M字節。

3	知識產權的問題
本文檔描述的CAST-128加密算法可以在世界范圍內免費用于商業和非商業用途。

4	安全性的問題
本備忘錄完全是關于安全性的，它描述了一種算法專門用于加密的目的。

5	參考

   [Adams] Adams, C., "Constructing Symmetric Ciphers using the CAST
   Design Procedure", Designs, Codes, and Cryptography (to appear).

   [Web1] "Constructing Symmetric Ciphers using the CAST Design
   Procedure" (identical to [Adams] but available on-line) and "CAST
   Design Procedure Addendum", http://www.entrust.com/library.htm.

   [Web2] "CAST Encryption Algorithm Related Publications",
   http://adonis.ee.queensu.ca:8000/cast/cast.html.

6	作者地址

   Carlisle Adams
   Entrust Technologies
   750 Heron Road,
   Ottawa, Canada, K1V 1A7

   E-mail: cadams@entrust.com
   Phone:  +1.613.763.9008

7	附錄A  置換箱（S-Boxes）

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S-Box S3
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S-Box S4
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