xtax-encryption 0.1.2

Trait-only encryption provider interface — used by xtax-blob-storage and other crates.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130

//! # xtax-encryption
//!
//! Trait-only encryption provider interface — no backend, no storage, no I/O
//! decisions. Implement [`EncryptionProvider`] to plug any encryption scheme
//! into crates like `xtax-blob-storage`.
//!
//! ## Crate architecture
//!
//! ```text
//! xtax-encryption               ←  this crate (trait + error types only)
//!      ↑
//! xtax-blob-storage             ←  re-exports and uses the trait
//! ```
//!
//! ## Usage
//!
//! ```rust,no_run
//! use async_trait::async_trait;
//! use tokio::io::{AsyncRead, AsyncWrite};
//! use xtax_encryption::{EncryptionProvider, EncryptionResult};
//!
//! struct NoopEncryption;
//!
//! #[async_trait]
//! impl EncryptionProvider for NoopEncryption {
//!     async fn encrypt_stream(
//!         &self,
//!         _input: &mut (dyn AsyncRead + Send + Unpin),
//!         _output: &mut (dyn AsyncWrite + Send + Unpin),
//!     ) -> EncryptionResult<Vec<u8>> {
//!         Ok(vec![])
//!     }
//!
//!     async fn decrypt_stream(
//!         &self,
//!         _input: &mut (dyn AsyncRead + Send + Unpin),
//!         _output: &mut (dyn AsyncWrite + Send + Unpin),
//!         _header_bytes: &[u8],
//!     ) -> EncryptionResult<()> {
//!         Ok(())
//!     }
//!
//!     async fn rekey_header(&self, _header_bytes: &[u8]) -> EncryptionResult<Option<Vec<u8>>> {
//!         Ok(None)
//!     }
//! }
//! ```
//!
//! ## Feature flags
//!
//! This crate has no features — it's a minimal dependency.

use async_trait::async_trait;
use tokio::io::{AsyncRead, AsyncWrite};

// ---------------------------------------------------------------------------
// Error type
// ---------------------------------------------------------------------------

/// An error returned by [`EncryptionProvider`] methods.
#[derive(Debug, thiserror::Error)]
#[non_exhaustive]
pub enum EncryptionError {
    /// Encrypt or decrypt operation failed.
    #[error("encryption operation failed: {message}")]
    Operation {
        /// Human-readable description of the failure.
        message: String,
        /// Optional underlying cause.
        #[source]
        source: Option<Box<dyn std::error::Error + Send + Sync + 'static>>,
    },

    /// Invalid or corrupted header data.
    #[error("invalid encryption header: {0}")]
    InvalidHeader(String),

    /// I/O error during encryption or decryption.
    #[error(transparent)]
    Io(#[from] std::io::Error),
}

/// Convenience alias for `Result<T, EncryptionError>`.
pub type EncryptionResult<T> = Result<T, EncryptionError>;

// ---------------------------------------------------------------------------
// EncryptionProvider trait
// ---------------------------------------------------------------------------

/// Encryption provider — abstracts the encryption operations needed
/// by encrypted storage layers.
///
/// This trait allows any crate to work with a pluggable encryption backend
/// that supports detached-header stream encryption.
///
/// # Implementations
///
/// - Must be [`Send`] + [`Sync`] (required by async storage layers).
/// - The [`encrypt_stream`](EncryptionProvider::encrypt_stream) method
///   **must** flush the output stream before returning.
/// - The returned header bytes are stored separately from the encrypted data
///   and later passed back to [`decrypt_stream`](EncryptionProvider::decrypt_stream).
#[async_trait]
pub trait EncryptionProvider: Send + Sync {
    /// Encrypt data from `input` and write the encrypted stream to `output`.
    ///
    /// Returns the serialisable encryption header that must be stored
    /// alongside the data (e.g. as a separate blob).
    async fn encrypt_stream(
        &self,
        input: &mut (dyn AsyncRead + Send + Unpin),
        output: &mut (dyn AsyncWrite + Send + Unpin),
    ) -> EncryptionResult<Vec<u8>>;

    /// Decrypt data from `input` using the previously stored `header_bytes`
    /// and write plaintext to `output`.
    async fn decrypt_stream(
        &self,
        input: &mut (dyn AsyncRead + Send + Unpin),
        output: &mut (dyn AsyncWrite + Send + Unpin),
        header_bytes: &[u8],
    ) -> EncryptionResult<()>;

    /// Try to re-key (re-wrap) an existing encryption header with the
    /// current master key.
    ///
    /// - Returns `None` if the header is already using the current key.
    /// - Returns `Some(new_header_bytes)` if the header was re-wrapped.
    async fn rekey_header(&self, header_bytes: &[u8]) -> EncryptionResult<Option<Vec<u8>>>;
}