Scientists at Northwestern University say they have harnessed the properties of light to encrypt information into code that can be cracked only one way: by breaking the physical laws of nature. There is growing interest in using quantum cryptography for commercial and military applications because of the technology’s apparent ability to guarantee invulnerability. Quantum cryptography, however, still suffers from one major limitation. As it stands today, all quantum cryptography techniques only work over dedicated fiber-optic lines–not over the Internet–and over distances no greater than about 90 kilometers from one point to another. That may be changing.