Struct StaticCodex 

pub struct StaticCodex { /* private fields */ }

Involution-based byte-swap codex backed by a 256-byte lookup table.

The table is held in a crate-internal LockedBytes buffer (mlock’d, zeroed on drop) since knowledge of the table is equivalent to knowledge of the transformation.

Implementations

impl StaticCodex

pub fn from_swaps(swaps: &[(u8, u8)]) -> Result<Self>

Construct a codex from a list of swap pairs.

Each (a, b) in swaps means “byte a encodes to b and b encodes to a.” Bytes not mentioned in any pair are fixed points (encode to themselves). Self-swaps ((x, x)) are accepted as no-ops.

Errors

Returns Error::Codex if a byte appears in more than one swap pair — that would force the table to disagree with itself and break the involution property.

Examples

use key_vault::{Codex, StaticCodex};

// Swap the ASCII digit '0' with '#' and 'A' with '@'.
let codex = StaticCodex::from_swaps(&[(b'0', b'#'), (b'A', b'@')]).unwrap();
assert_eq!(codex.encode(b'0'), b'#');
assert_eq!(codex.encode(b'#'), b'0');
assert_eq!(codex.encode(b'B'), b'B'); // not in any swap, fixed point
// Involution holds:
for byte in 0u8..=255 {
    assert_eq!(codex.decode(codex.encode(byte)), byte);
}

pub fn random_involution() -> Result<Self>

Generate a random involution with no fixed points.

Pairs up all 256 bytes uniformly at random and writes the resulting permutation into the lookup table. Every byte transforms to a different byte.

Errors

Returns Error::Internal if the OS CSPRNG fails — same failure mode as everywhere else in the crate.

Examples

use key_vault::{Codex, StaticCodex};

let codex = StaticCodex::random_involution().unwrap();
// Involution: applying it twice returns the original byte.
for byte in 0u8..=255 {
    assert_eq!(codex.decode(codex.encode(byte)), byte);
}
// No fixed points: every byte transforms to a different byte.
for byte in 0u8..=255 {
    assert_ne!(codex.encode(byte), byte);
}

Trait Implementations

impl Codex for StaticCodex

fn encode(&self, byte: u8) -> u8

Transform a byte on the way into storage.

fn decode(&self, byte: u8) -> u8

Transform a byte on the way out of storage.

impl Debug for StaticCodex

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

Formats the value using the given formatter.