pub struct Choice(_);
Expand description
The Choice
struct represents a choice for use in conditional assignment.
It is a wrapper around a u8
, which should have the value either 1
(true)
or 0
(false).
The conversion from u8
to Choice
passes the value through an optimization
barrier, as a best-effort attempt to prevent the compiler from inferring that
the Choice
value is a boolean. This strategy is based on Tim Maclean’s
work on rust-timing-shield
, which attempts to provide
a more comprehensive approach for preventing software side-channels in Rust
code.
The Choice
struct implements operators for AND, OR, XOR, and NOT, to allow
combining Choice
values. These operations do not short-circuit.
Implementations§
Trait Implementations§
source§impl BitAndAssign<Choice> for Choice
impl BitAndAssign<Choice> for Choice
source§fn bitand_assign(&mut self, rhs: Choice)
fn bitand_assign(&mut self, rhs: Choice)
&=
operation. Read moresource§impl BitOrAssign<Choice> for Choice
impl BitOrAssign<Choice> for Choice
source§fn bitor_assign(&mut self, rhs: Choice)
fn bitor_assign(&mut self, rhs: Choice)
|=
operation. Read moresource§impl BitXorAssign<Choice> for Choice
impl BitXorAssign<Choice> for Choice
source§fn bitxor_assign(&mut self, rhs: Choice)
fn bitxor_assign(&mut self, rhs: Choice)
^=
operation. Read moresource§impl ConditionallySelectable for Choice
impl ConditionallySelectable for Choice
source§impl ConstantTimeEq for Choice
impl ConstantTimeEq for Choice
source§impl From<Choice> for bool
impl From<Choice> for bool
source§fn from(source: Choice) -> bool
fn from(source: Choice) -> bool
Convert the Choice
wrapper into a bool
, depending on whether
the underlying u8
was a 0
or a 1
.
Note
This function exists to avoid having higher-level cryptographic protocol implementations duplicating this pattern.
The intended use case for this conversion is at the end of a
higher-level primitive implementation: for example, in checking a keyed
MAC, where the verification should happen in constant-time (and thus use
a Choice
) but it is safe to return a bool
at the end of the
verification.