# No of keys used in Triple DES Algorithm

I am studying Triple DES.

I have got two basic questions. One, why are we following a sequence like encrypt(decrypt(encrypt)); what is the problem using a sequence encrypt(encrypt(encrypt))?

Second, why are we not using a single long key (say 168 independent key bits) in lieu of three individual 56 bits keys?

Thanks.

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For the second question, a single key $k \in \left\{0,1\right\}^{168}$ can be trivially converted back and forth from three keys $k_1, k_2, k_3 \in \left\{0,1\right\}^{56}$ – there is no semantic difference between the two. DES itself operates only on 56-bit keys, and triple-DES requires three independent DES operations. Software that implements triple-DES can trivially be written to either accept a single 168-bit key or three 56-bit keys.