# Prime computation for Diffie Hellman

While reading some cryptographic RFCs, came across the Diffie Hellman prime computation formula:

2^1024 - 2^960 - 1 + 2^64 * { [2^894 pi] + 129093 }

I am curious what the expression [2^894 pi] means here. The part specifically confusing me is the space between 2^894 and pi. It cannot be a multiplication operation as that does not give me the correct result. I am sure the answer is straightforward for someone with mathematical background...

It's multiplication of 2^894 and pi.
(2^1024 - 2^960 - 1 + 2^64 * ( (2^894 * pi) + 129093))

• The bits aren't ignored. It's just not an integer as given. Add floor() and you'll see it's the same size: wolframalpha.com/input/…*+%28+%282%5E894+*pi%29+%2B+129093+%29%29+in+hexadecimal – Rob Napier Mar 9 at 0:28