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Would it be possible to use a block cipher such as CBC in order to encrypt a wireless communication? For example, could I use CBC-MAC, on each block, for encryption for WiFi?

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  • $\begingroup$ A block cipher with block size of n bits under a user given key is simply a bijective mapping of n bits to n bits. The result of encryption can be transmitted in any kind of channels (including on paper via normal mail). Thus I don't yet understand why "wireless communications" would make any difference as far as the security of encryption processing is concerned. $\endgroup$ – Mok-Kong Shen Nov 10 '16 at 22:15
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    $\begingroup$ CBC isn't a block cipher. $\endgroup$ – user253751 Nov 10 '16 at 23:34
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    $\begingroup$ Your question is like asking whether machine language can be used to build a self-driving car. The answer is yes, but I hope you can see the problem with the question—it leaves out all the critically important stuff in between the primitives and the desired goal. $\endgroup$ – Luis Casillas Nov 11 '16 at 1:42
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Yes, you can encrypt wireless communication using a block cipher in a specific mode of operation to provide confidentiality. Transport modes also require integrity and authentication to protect against active attacks such as man-in-the-middle attacks.

CBC is however not a block cipher, and neither is CBC-MAC. CBC is a block cipher mode of operation used to provide confidentiality while CBC-MAC is a message authentication code used to provide integrity and authenticity. These constructs use a block cipher such as AES to provide this kind of functionality.

AES (and DES, 3DES, blowfish, Serpent, threefish etc. etc.) are block ciphers. They need to be used with a mode of operation such as CBC to provide confidentiality of messages; they cannot provide such functionality without a mode of operation. A mode of operation also requires an IV or nonce if the key is ever reused. In transport protocols the keys are usually kept for the duration of a session.

WPA2 may use the CCMP which combines AES in CTR (counter) mode for encryption and AES in CBC-MAC mode for integrity and authentication of messages.

Note that the protection of messages is just part of the protocol. Entity authentication and session key establishment require additional cryptographic primitives (a cryptographic primitive is an algorithm such as AES or RSA that is used within a larger scheme).

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  • $\begingroup$ Thanks @maartenbodewes, so would it be correct to say that CBC-MAC could not take the place of AES for WPA2? $\endgroup$ – tpm900 Nov 10 '16 at 22:10
  • $\begingroup$ AES is used within CBC-MAC. So that statement would not make sense. CBC-MAC requires a block cipher to operate, and that block cipher is usually AES (although any secure block cipher will do, preferably one with a 128 bits block size such as AES). $\endgroup$ – Maarten Bodewes Nov 10 '16 at 22:11
  • $\begingroup$ I had meant replace AES in CTR mode with CBC-MAC (should have reread the comment before I posted it) $\endgroup$ – tpm900 Nov 10 '16 at 22:16
  • $\begingroup$ CTR mode is used to provide confidentiality of messages, CBC-MAC provides integrity and authenticity. As they provide different functionality altogether, one can not replace the other. $\endgroup$ – Maarten Bodewes Nov 10 '16 at 22:20

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