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).
With the nightly
feature enabled, 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 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.