next up previous
Next: Nikita and Michael Up: Microsoft Digital Rights Management Previous: Microsoft Digital Rights Management

Microsoft's Favorite Elliptic Curve

The elliptic curve used in MS-DRM is an elliptic curve over the finite field $ k=\mathbb{Z}/p\mathbb{Z}$, where

$\displaystyle p=785963102379428822376694789446897396207498568951.
$

As Beale Screamer remarks, this modulus has high nerd appeal because in hexadecimal it is
89ABCDEF012345672718281831415926141424F7,
which includes counting in hexadecimal, and digits of $ e$, $ \pi$, and $ \sqrt{2}$. The Microsoft elliptic curve $ E$ is

$\displaystyle y^2 = x^3$ $\displaystyle + 317689081251325503476317476413827693272746955927x$    
  $\displaystyle \qquad +79052896607878758718120572025718535432100651934.$    

We have

$\displaystyle \char93  E(k) = 785963102379428822376693024881714957612686157429,$

and the group $ E(k)$ is cyclic with generator

$\displaystyle B$ $\displaystyle = (771507216262649826170648268565579889907769254176,$    
  $\displaystyle \qquad 390157510246556628525279459266514995562533196655).$    



William A Stein 2001-11-20