secure-gate 0.9.0-rc.13

Secure wrappers for secrets with explicit access and mandatory zeroization — no_std-compatible, zero-overhead library with audit-friendly access patterns.
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//! Hexadecimal encoding trait.
//!
//! > **Import path:** `use secure_gate::ToHex;`
//!
//! This trait provides secure, explicit encoding of byte data to lowercase
//! (or uppercase) hexadecimal strings. It is intended for intentional export
//! only (QR codes, audited logs, API responses).
//!
//! Requires the `encoding-hex` feature.
//!
//! # Security Notes
//!
//! - **Full secret exposure**: The resulting string contains the **entire** secret.
//!   Always treat output as sensitive; do not log or persist without protection.
//! - **Always wiped**: `to_hex()` / `to_hex_upper()` return
//!   [`EncodedSecret`](crate::EncodedSecret), which wraps `Zeroizing<String>`, redacts
//!   its `Debug`, and wipes on drop.
//!   There is no unprotected variant. `.into_inner()` is the named point where that
//!   protection ends.
//! - **Audit visibility**: Direct calls (`key.to_hex()` / `key.to_hex_upper()`) do **not** appear in
//!   `grep expose_secret` / `grep with_secret` audit sweeps. For audit-first teams or
//!   multi-step operations, prefer `with_secret(|b| b.to_hex())` — the borrow checker
//!   enforces the reference cannot escape the closure.
//! - **Decoding lives elsewhere**: this module encodes. For the reverse direction and
//!   its untrusted-input rules see `FromHexStr`; validate hex
//!   strings upstream before wrapping
//!   in secrets.
//!
//! # Example
//!
//! ```rust
//! # #[cfg(feature = "encoding-hex")]
//! use secure_gate::{Fixed, ToHex, RevealSecret};
//! # #[cfg(feature = "encoding-hex")]
//! {
//! let secret = Fixed::new([0x0au8, 0x0bu8, 0x0cu8, 0x0du8]);
//!
//! // Blanket impl on the inner byte array (via with_secret):
//! let hex = secret.with_secret(|s| s.to_hex());
//! assert_eq!(&*hex, "0a0b0c0d");
//!
//! let hex_upper = secret.with_secret(|s| s.to_hex_upper());
//! assert_eq!(&*hex_upper, "0A0B0C0D");
//!
//! // Wrapper method (Direct Fixed<[u8; N]> API — same result):
//! assert_eq!(&*secret.to_hex(), "0a0b0c0d");
//! }
//! ```
#[cfg(all(feature = "encoding-hex", feature = "alloc"))]
use base16ct;

/// Extension trait for encoding byte data as hexadecimal strings.
///
/// *Requires feature `encoding-hex`.*
///
/// Blanket-implemented for `AsRef<[u8]>` + [`EncodableBytes`](super::EncodableBytes) (byte slices, arrays, `Vec<u8>`),
/// and implemented directly on the byte-shaped wrappers (`Fixed<[u8; N]>`,
/// `Dynamic<Vec<u8>>`). To encode a secret wrapper, call `key.to_hex()` with this
/// trait in scope (ergonomically safest for single operations — no reference in the
/// caller's hands), or use `with_secret(|b| b.to_hex())` for multi-step operations
/// or when audit-greppability matters.
#[cfg(all(feature = "encoding-hex", feature = "alloc"))]
pub trait ToHex {
    /// Encode bytes as lowercase hexadecimal.
    fn to_hex(&self) -> crate::EncodedSecret;

    /// Encode bytes as uppercase hexadecimal.
    fn to_hex_upper(&self) -> crate::EncodedSecret;
}

// Blanket impl over AsRef<[u8]> + EncodableBytes (e.g. &[u8], Vec<u8>, [u8; N]).
// encode_string requires alloc — the trait itself is alloc-gated.
#[cfg(all(feature = "encoding-hex", feature = "alloc"))]
impl<T: AsRef<[u8]> + super::EncodableBytes + ?Sized> ToHex for T {
    #[inline(always)]
    fn to_hex(&self) -> crate::EncodedSecret {
        crate::EncodedSecret::new(base16ct::lower::encode_string(self.as_ref()))
    }

    #[inline(always)]
    fn to_hex_upper(&self) -> crate::EncodedSecret {
        crate::EncodedSecret::new(base16ct::upper::encode_string(self.as_ref()))
    }
}