Javascript crypto lib performance comparison

[nilstoedtmann]

CC @jhb

As long as WebCrypto hasn't arrived, we have to use other libs for JS clients. Accidentally, we are using Leemon Baird's BigInt library, but we are not too happy with it, and we need other stuff as well (e.g. sha256 and PKCS1).

We should do performance tests with the most promising JS crypto libs:

• BigInt encoding/decoding, BigInt inversion (= calculate unblinder) and low-exponent exponentiation (blinding) with these libs: Baird, Wu, Shapiro, Shop-js (Hanewinkel says that was the fastest RSA he found) and (RSA test only) OpenPGP.js and Forge
• Sha256 tests with SJCL, Crypto-js, jsSHA/OpenPGP.js and Forge