Struct Hints 

pub struct Hints<H, const S: usize> { /* private fields */ }

Batch of Hints that enforces inner vector size. In addition, Hints::new shuffles inputs, and also mitigates some timing leaks, while all constructors ensure uniqueness of supplied blinded public keys.

1. If fewer HintSeed items than S are supplied during creation, decoy HintSeeds will fill the remaining slots.
2. A new temporary K::SecretKey is generated, which is used as a one-off contribution to the group secrets used to encrypt the respective Hint’s messages.
3. In order to make sure passive attackers don’t know which Hint to brute force, the Hints order should not be deterministic, so decoy and real Hints get shuffled before the result is returned.
4. Before a Hints batch gets constructed, all the supplied HintSeeds are checked for duplicate K::PublicKeys.

In aggregate, this ensures that even if the same HintSeed set is used to create multiple Hints instances, they are indistinguishable to passive observers that want to infer communication patterns by repeatedly polling a server or other intermediary.

Implementations

impl<K: KeyPair, A: Aead + KeyInit, L: ArraySize, const S: usize> Hints<Hint<K, A, L>, S>

where Hint<K, A, L>: HintSized<K, A, L> + Hinting<K, L>,

pub fn new( hint_seeds: &[HintSeed<K, L>], context: &[u8], csprng: &mut impl CryptoRng, ) -> Result<Self, Error>

where HintSeed<K, L>: Decoy, BlindedPublicKey<K>: Blinded,

Build shuffled batch of Hint instances from a HintSeed slice containing at most S items, context, and an RNG, resulting in Hints with size S.

Security

Although this method mitigates leaking execution timing as best as feasible and can be broadly described as having O(1) complexity, it also dynamically creates decoy hint seeds, which forces access patterns over non-contigouos memory and in turn cannot provide resistance to various side channel attacks. It should only be used in settings where your threat model does not include local adversaries.

pub fn from_pre_shuffled<V: Validation>( hint_seeds: &[&HintSeed<K, L>], context: &[u8], csprng: &mut impl CryptoRng, ) -> Result<Self, Error>

where BlindedPublicKey<K>: Blinded,

Build batch of Hint instances from a pre-shuffled HintSeed slice with length of S, context, and an RNG.

Security

Requires supplying either Validate or, if the hazmat feature is enabled, hazmat::Passthru as a type parameter. The former ensures inputs do not risk accidental disclosure, the latter skips validation altogether and may leak information.

Note: Even when validating the supplied hint seeds slice, it cannot test whether inputs are pre-shuffled, hence it merely checks if the inputs have the expected length and don’t contain duplicates. However, provided the input’s memory layout is contiguous and underlying primitives used have constant-time implementations, this method inherits the properties of the cryptographic libraries used with the input types.

pub fn validate_hint_seeds(hint_seeds: &[&HintSeed<K, L>]) -> Result<(), Error>

where BlindedPublicKey<K>: Blinded,

Validate that the supplied slice of HintSeeds only contains BlindedPublicKeys

pub fn as_slice(&self) -> &[Hint<K, A, L>]

View as slice.

pub fn from_bytes(bytes: &[u8]) -> Result<Self, Error>

Deserialize from byte slice.

pub fn to_bytes(self) -> Vec<u8>

Serialize to byte vector.

Trait Implementations

impl<H: Clone, const S: usize> Clone for Hints<H, S>

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<H: Debug, const S: usize> Debug for Hints<H, S>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.