On Wed, Sep 11, 2013 at 9:56 AM, Mike Miller <mbmiller+l at gmail.com> wrote: > On Wed, 11 Sep 2013, Jay Kline wrote: > >> On Wed, Sep 11, 2013 at 8:50 AM, Michael Greenly <mgreenly at gmail.com> >> wrote: >> >>> S/Mime uses a centralized certificate authority. PGP/GPG is >>> decentralized. There's no question that PGP/GPG is preferable over S/Mime >>> because of this >> >> >> S/MIME and GPG/GPG use the same crypto. > > > What do they use? Is it very strong? > They both (generally) support RSA for the public/private keypairs (varying sizes are supported), which will be used for digital signatures and block cipher key wrapping. For the block cyphers, 3DES and AES are common. Both S/MIME and GPG support more algorithms (you would need to go look ad the documentation for specific software versions to see what is supported). What I was getting at, though, was the crypto-security of the two are based more on which algorithms and keys you choose than S/MIME vs GPG itself. I would think more about how you perceive trust between end users of the system and how that fits your needs. S/MIME will be more centralized, and can be good when you have a trusted issuer you can take advantage of. A corporate entity is a good example- a CA for the company means any employee can trust the credentials of another employee issued by that CA. S/MIME is also good if you already have an existing SSL-based infrastructure in place, you can use it without adding many new parts. GPG is decentralized forming a "web of trust", and is better when you have ad-hoc communications or dont trust a central authority (like Comodo CAs, for example). Interestingly, GPG actually supports the S/MIME format, showing how interchangeable the systems can be. Are they strong? As long as you avoid known bad ciphers (3DES is fairly weak by todays standards) and sufficient key sizes (RSA should be 2048bit and AES 256bit) they are "strong" . Strong enough to stop the NSA? I wont venture a guess on that- plenty of speculation in the news lately about it. The NSA maintains two "suites" of algorithms, Suite A and Suite B. Suite A is classified, so we dont really know what is there. Suite B is publicly released, and is the reference for US Gov't agencies and partners for encrypting various kinds of data. Sticking with Suite B algorithms is a pretty safe bet that even if the NSA *can* break them, it takes considerable effort to do so, and generally there are no other groups capable of breaking them. Jay