Key Length VS. Cryptographic Strength

Comparison of Time and Money Needed to Break Different Length Keys

Length of Crytographic Key

$0.1 M2 sec.35 hrs.1 yr.70000 yrs.10E19 yrs.
$1.0 M.2 sec.3.5 hrs.37 days7000 yrs.10E18 yrs.
$100 M2 millisec.2 min.9 hrs.70 yrs.10E16 yrs.
$1.0 B.2 millisec.13 sec.1 hr.7 yrs.10E15 yrs.
$100 B2 microsec.1 sec.32 sec.24 days10E13 yrs.
Source: B. Schneier, Applied Cryptography, 2nd ed., 1996.

Secret-Key and Public-Key Lengths for Equivalent Levels of Security

Secret-Key LengthPublic-Key Length
56 bits384 bits
64 bits512 bits
80 bits768 bits
112 bits1792 bits
128 bits2304 bits