Enum NoncePolicy 

pub enum NoncePolicy {
    RandomStored,
    DerivedFromContext {
        context: Vec<u8>,
    },
}

Where a sealed payload’s base nonce comes from — the choice every caller that seals or opens one states outright.

Invariant: a derived base must be unique per plaintext

XChaCha20-Poly1305 offers no margin for nonce reuse. Two different plaintexts sealed under one key and one nonce leak their XOR and forfeit authentication, and that failure is silent — everything still encrypts, decrypts, and round-trips. Self::DerivedFromContext is therefore only safe while its context differs whenever the plaintext does, which is why the context is part of the policy rather than something a caller can forget to pass, and why the choice is a named variant rather than a flag or a default.

Variants

RandomStored

A base nonce drawn at random and written into the header, ahead of the chunks. Safe however the payload is addressed, at the cost of 24 stored bytes and a base only the stored header carries.

DerivedFromContext

A base nonce derived by HKDF from the sealing key and context, stored nowhere, so the same payload always seals to the same bytes and a reader that knows the context can open any chunk without reading a base first.

context must differ whenever the plaintext does. It holds for a blob because the context is minted from the blob’s semantic key, which for an opaque blob is {namespace}/opaque/{locator_hash}, and the locator hash covers the plaintext hash — so two different plaintexts cannot share a context without a SHA-256 collision. Re-sealing identical bytes under an identical context reproduces an identical base, which is fine: it reproduces identical ciphertext, not a second message under one nonce.

Any change to how a payload is addressed must preserve that. A locator that stopped folding in the plaintext hash, or a context minted from something that outlives the payload’s content (a bare row id, a stable path), would let one key seal two different plaintexts under one nonce.

Fields

context: Vec<u8>

Trait Implementations

impl Clone for NoncePolicy

fn clone(&self) -> NoncePolicy

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for NoncePolicy

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

Formats the value using the given formatter.

impl PartialEq for NoncePolicy

fn eq(&self, other: &NoncePolicy) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Eq for NoncePolicy

impl StructuralPartialEq for NoncePolicy