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I was asked to encrypt/decrypt a string using MACTripleDES. Is there any difference between MACTripleDES and TripleDES? If, where exactly is the difference between both?

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  • $\begingroup$ You mean this thing? If so, this question on SO might be helpful. $\endgroup$ – Ilmari Karonen Jan 7 '16 at 16:24
  • $\begingroup$ thanks @IlmariKaronen, i've seen the msdn but the example showing to encrypt/decrypt the file not string. $\endgroup$ – Balaji Marimuthu Jan 7 '16 at 16:30
  • $\begingroup$ That would be a valid question on Stack Overflow, but not here. (Or you could just look at the documentation, and specifically the ComputeHash(Byte[]) method). Also, you cannot "encrypt" or "decrypt" anything with a MAC; that's not what they're for. $\endgroup$ – Ilmari Karonen Jan 7 '16 at 16:46
  • $\begingroup$ Cross-posted on Stack Overflow: How to encrypt decrypt string using MACTripleDES? $\endgroup$ – Artjom B. Jan 8 '16 at 11:40
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Triple DES is a block cipher. (Specifically, it's a variant of the old DES block cipher with better security, but several times lower performance.) You can use it to encrypt small blocks of data (64 bits = 8 bytes, for Triple DES), but what it's really useful for is as a building block for other cryptographic schemes, such as stream encryption or message authentication codes (MACs).

MACTripleDES is, apparently, a class in the Microsoft .NET framework that provides some kind of a MAC using Triple DES. The documentation doesn't actually seem to say which MAC construction it uses, but this answer on SO implies that it's classic CBC-MAC.

Note that raw CBC-MAC is not, by itself, secure for variable-length messages. To make it secure, you need to use one of the techniques described in the linked Wikipedia article (prepending the length to the message, encrypting the output with a different key, or using a separate MAC key for each message length), or use a more modern MAC algorithm like CMAC instead. (You may also wish to consider using a more modern cipher with a larger key and block size and better performance than Triple DES, such AES.)

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