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"RSA-640", a 640 bit (193-digits) number was factored in 2005 using 30 CPU-years on a cluster of 2.2 GHz Opterons (5 months elapsed). The graph below extrapolates this to other lengths, assuming complexity scales as:
64 9 n log2HnL
3
In[150]:= f@n_D := Exp@H64 ê 9 * n * Log@nD^2L^H1 ê 3LDShow@LogPlot@f@nD ê f@640D * 30, 8n, 350, 640 * 2<, AxesLabel Ø 8"Length HbitsL", "Effort HCPU-yearsL"<D, ListLogPlot@88640, 30<<, PlotMarkers Ø 8Automatic, Medium<DD
Out[151]=Ê
400 600 800 1000 1200 Length HbitsL 0.1 100 105 108 Effort HCPU-yearsL
If you're worried about someone spending 30 CPU-years to crack your email chatter, what could you do? Double your key length. That will slow en-/decryption by < 8 x (they're sub-cubic algorithms), but slow factoring by 10^8 x.
'Eqf-640", a 640.bit (1g3-digits) number was factored in 2OO5 using gO CPU-years
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lf you?e worried about someone spending g0 Cpu-years to crack your emaif chatter, what could vou do? Double vour kei lenoth. That n;ill slow en-/decryption by **i (rhey?e g.glklic atgoritnmS;, but stow
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