pub struct Choice(/* private fields */);
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 for Choice
impl BitAndAssign for Choice
source§fn bitand_assign(&mut self, rhs: Choice)
fn bitand_assign(&mut self, rhs: Choice)
&=
operation. Read moresource§impl BitOrAssign for Choice
impl BitOrAssign for Choice
source§fn bitor_assign(&mut self, rhs: Choice)
fn bitor_assign(&mut self, rhs: Choice)
|=
operation. Read moresource§impl BitXorAssign for Choice
impl BitXorAssign 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§fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self
fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self
source§fn conditional_assign(&mut self, other: &Self, choice: Choice)
fn conditional_assign(&mut self, other: &Self, choice: Choice)
source§fn conditional_swap(a: &mut Self, b: &mut Self, choice: Choice)
fn conditional_swap(a: &mut Self, b: &mut Self, choice: Choice)
self
and other
if choice == 1
; otherwise,
reassign both unto themselves. Read moresource§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.
impl Copy for Choice
Auto Trait Implementations§
impl Freeze for Choice
impl RefUnwindSafe for Choice
impl Send for Choice
impl Sync for Choice
impl Unpin for Choice
impl UnwindSafe for Choice
Blanket Implementations§
source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
source§impl<T> CloneToUninit for Twhere
T: Clone,
impl<T> CloneToUninit for Twhere
T: Clone,
source§unsafe fn clone_to_uninit(&self, dst: *mut T)
unsafe fn clone_to_uninit(&self, dst: *mut T)
clone_to_uninit
)