Re:CTTK: Constant-Time Toolkit
by userbinator on Sunday February 25, 2018 @10:24PM
(#16462837)
Many X86 instructions appear to be constant time, but under certain conditions are not.
One not-so-well-known and possibly surprising fact is that on the NetBurst (P4) microarchitecture, 32-bit arithmetic operations that produce a carry/borrow between the two 16-bit halves introduce an extra clock cycle of latency, because the ALUs are only 16 bits wide.
One not-so-well-known and possibly surprising fact is that on the NetBurst (P4) microarchitecture, 32-bit arithmetic operations that produce a carry/borrow between the two 16-bit halves introduce an extra clock cycle of latency, because the ALUs are only 16 bits wide.