Today's systems must anticipate future attacks. Any comprehensive system – whether for authenticated communications, secure data storage, or electronic commerce – is likely to remain in use for five years or more. It must be able to withstand the future: smarter attackers, more computational power, and greater incentives to subvert a widespread system. There won't be time to upgrade it in the field.

History has taught us: never underestimate the amount of money, time, and effort someone will expend to thwart a security system. It's always better to assume the worst. Assume your adversaries are better than they are. Assume science and technology will soon be able to do things they cannot yet. Give yourself a margin for error. Give yourself more security than you need today. When the unexpected happens, you'll be glad you did. — Bruce Schneier, "Why Cryptography Is Harder Than It Looks" 1997