• Reading carefully the CWSP Official study guide and other documentations related to security I come into the conclusion that here must be an error within the study guide?¡é?€?|

    They say on page 218 (Encryption chapter)
    Stream cipher is faster than block cipher it operates on smaller units of plaintext.
    The encryption of any particular plaintext with a block cipher will result in the same cipher text when the same key is used.

    With a stream cipher, the transformation of these smaller plaintext units will vary, depending on when they are encountered during the encryption process. "

    Looking at another document about encryption in WLAN made by Cisco I can read :

    The process of encryption described for stream ciphers and block ciphers is known as Electronic Code Book (ECB) mode encryption.With ECB mode encryption, the same plain-text input always generates the same cipher-text output.

    This is a potential security threat because eavesdroppers can see patterns in the cipher-text and start making educated guesses about what the original plain-text is.

    There are two encryption techniques to overcome this issue:
    ?¡é?€?¡é Initialization vectors
    ?¡é?€?¡é Feedback modes

    An initialization vector (IV) is used to alter the key stream. The IV is a numeric value that is concatenated to the base key before the key stream is generated. Every time the IV changes, so does the key stream.

    Feedback modes are modifications to the encryption process to prevent a plain-text message from generating the same cipher-text during encryption. Feedback modes are generally used with block ciphers, and the most common feedback mode is known as cipher block chaining (CBC) mode.

    So, who should I believe ? looking at several documentation it looks like that stream cipher is part of the ECB encryption , that means it will always (by default) generate the same ciphered text.

    Thanks for letting me know your opinion about it... it would help me to prepare the CWSP exam !!



  • Hi Chris of Bordeaux:

    I have always thought of ECB as a block cipher technique and not a stream cipher technique. All my current googling bears this out:,,sid14_gci344944,00.html

    I hope this helps. Thanks. /criss

  • Hi Criss,
    Thanks for these very useful links sent on the forum.

    According to the link there are 4 modes of operation for block cipher :
    * Electronic Code Book (ECB) (which encryption? RC5, DES, 3DES, AES ?)
    * Cipher Block Chaining (CBC) (used by AES or authenticity purpose)
    * Cipher Feedback (CFB)
    * Output Feedback (OFB)

    At least the explanation in this page are clearer to me than the various definitions in the CWSP Guide.

    However the ECB is claimed to be a stream cipher technique as well as a Block cipher technique in the following document issued by Cisco in 2002 :
    White paper "A Comprehensive Review of 802.11 Wireless LAN Security and the Cisco Wireless Security Suite " (page 10, chapter entitled "3.1. Stream Ciphers and Block Ciphers").

    At this point I don't know who is right eventhough I would say I would believe the links you have posted...

    May be a specialist will clear it out definitely.

    Thanks for your contribution !


  • Hi Chris:

    It looks to me like the Cisco writer/editor was making a valid point common to stream and block ciphers and mistakenly used ECB to refer to both.

    I hope this helps. Thanks. /criss

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