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Is the 3DES encryption algorithm the best choice for S/MIME protocol?

The triple DES encryption algorithm was originally designed for the S/MIME protocol, but is it still the best choice for encryption? In this expert response, Randall Gamby describes the advantages and disadvantages to using 3DES.

How can 3DES symmetric encryption be implemented in the S/MIME protocol?
Actually, the 3DES encryption algorithm was part of the original S/MIME protocol. However, 3DES -- also known as Triple DES, or the Triple Data Encryption Standard -- is based on the DES algorithm developed by an IBM team in 1974. Triple DES was originally designed to run in specialized hardware, so it's considered computationally expensive on general-purpose processors.

Because of the limitations of the key lengths used in 3DES and its poor execution on general-purpose computers, S/MIME eventually adopted AES as the standard for its encryption. AES, also known as Rijndael and FIPS-197, is a symmetric block cipher that can accept variable block and key lengths up to 256-bits and isn't restricted to the less secure 64-bit key lengths of 3DES. Plus, it would probably run a bit better on your server than 3DES. Because of this, it's hard to recommend using 3DES (even though it should be technically possible) because ultimately you'll be taking a giant step backward. But assuming you have a requirement due to a legacy system, I'd recommend doing some research on the Internet to find an old copy of the S/MIME protocol standard for guidance on how to integrate a 3DES encryption key into it.

This was last published in April 2010

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