Add tlog_mirror crate with wire format and default ticket authenticator

Cargo.toml

@@ -20,6 +20,7 @@ members = [
     "crates/tlog_core",
     "crates/tlog_cosignature",
     "crates/tlog_entry",
+    "crates/tlog_mirror",
     "crates/tlog_tiles",
     "crates/tlog_tiles_wasm",
     "crates/tlog_witness",
@@ -49,6 +50,7 @@ default-members = [
     "crates/tlog_core",
     "crates/tlog_cosignature",
     "crates/tlog_entry",
+    "crates/tlog_mirror",
     "crates/tlog_tiles",
     "crates/tlog_tiles_wasm",
     "crates/tlog_witness",
@@ -80,6 +82,10 @@ opt-level = 3
 debug = 1
 
 [workspace.dependencies]
+# aes-gcm-siv has no stable release on the current RustCrypto trait
+# batch (aead 0.6), so it stays on a pre-release (as does rsa, below);
+# the rc still resolves aead/cipher up to their stable releases.
+aes-gcm-siv = { version = "0.12.0-rc.3", default-features = false, features = ["aes", "alloc"] }
 anyhow = "1.0"
 axum = { version = "0.8", default-features = false, features = ["json", "matched-path"] }
 base64 = "0.22"
@@ -132,6 +138,7 @@ tlog_checkpoint = { path = "crates/tlog_checkpoint", version = "0.2.0" }
 tlog_core = { path = "crates/tlog_core", version = "0.2.0" }
 tlog_cosignature = { path = "crates/tlog_cosignature", version = "0.2.0" }
 tlog_entry = { path = "crates/tlog_entry", version = "0.2.0" }
+tlog_mirror = { path = "crates/tlog_mirror", version = "0.2.0" }
 tlog_tiles = { path = "crates/tlog_tiles", version = "0.2.0" }
 tlog_witness = { path = "crates/tlog_witness", version = "0.2.0" }
 tokio = { version = "1", features = ["sync"] }

crates/tlog_mirror/Cargo.toml

@@ -0,0 +1,29 @@
+[package]
+name = "tlog_mirror"
+# Held back from crates.io while c2sp.org/tlog-mirror stabilizes. Lift
+# the publish gate (and remove this comment) once the spec is final.
+publish = false
+version.workspace = true
+authors.workspace = true
+edition.workspace = true
+license.workspace = true
+readme.workspace = true
+homepage.workspace = true
+repository.workspace = true
+description = "An implementation of c2sp.org/tlog-mirror"
+categories = ["cryptography"]
+keywords = ["transparency", "mirror", "checkpoint", "crypto", "pki"]
+
+[package.metadata.release]
+release = false
+
+[lib]
+crate-type = ["rlib"]
+
+[dependencies]
+aes-gcm-siv.workspace = true
+base64.workspace = true
+byteorder.workspace = true
+rand.workspace = true
+thiserror.workspace = true
+tlog_core.workspace = true

crates/tlog_mirror/LICENSE

@@ -0,0 +1 @@
+../../LICENSE

crates/tlog_mirror/src/error.rs

@@ -0,0 +1,81 @@
+// Copyright (c) 2025-2026 Cloudflare, Inc. All rights reserved.
+// SPDX-License-Identifier: BSD-3-Clause
+
+//! Error types for `tlog_mirror`.
+
+use thiserror::Error;
+
+/// Errors returned when parsing tlog-mirror wire-format messages.
+#[derive(Debug, Error)]
+pub enum ParseError {
+    /// An IO error occurred while reading from the input stream.
+    #[error("io: {0}")]
+    Io(#[from] std::io::Error),
+
+    /// The `log_origin_size` u16 prefix advertised more bytes than were
+    /// available in the input.
+    #[error("log_origin truncated: advertised {advertised} bytes")]
+    LogOriginTruncated {
+        /// Size advertised by the wire `log_origin_size` u16.
+        advertised: u16,
+    },
+
+    /// The `log_origin` bytes were not valid UTF-8.
+    #[error("log_origin is not valid UTF-8")]
+    LogOriginNotUtf8,
+
+    /// `upload_start` was greater than `upload_end`.
+    #[error("upload_start ({start}) > upload_end ({end})")]
+    UploadRangeInverted {
+        /// `upload_start` from the wire.
+        start: u64,
+        /// `upload_end` from the wire.
+        end: u64,
+    },
+
+    /// `num_hashes` for a subtree consistency proof exceeded the spec's
+    /// maximum of 63.
+    #[error("num_hashes {0} exceeds spec maximum of 63")]
+    TooManyHashes(u8),
+
+    /// An entry package's entry count exceeded the spec's per-package
+    /// maximum of [`PACKAGE_ALIGNMENT`](crate::PACKAGE_ALIGNMENT) (256).
+    #[error("entry package has {0} entries, spec maximum is 256")]
+    TooManyEntries(u64),
+
+    /// The `text/x.tlog.mirror-info` body did not have exactly three
+    /// newline-terminated lines.
+    #[error("mirror-info body is malformed: {0}")]
+    MalformedMirrorInfo(&'static str),
+
+    /// A decimal field in the `text/x.tlog.mirror-info` body could not be
+    /// parsed as a `u64`.
+    #[error("mirror-info decimal field {field} could not be parsed: {value:?}")]
+    InvalidDecimal {
+        /// Field name (`tree_size` or `next_entry`).
+        field: &'static str,
+        /// Verbatim bytes from the wire.
+        value: String,
+    },
+
+    /// The base64-encoded ticket in a `text/x.tlog.mirror-info` body could
+    /// not be decoded.
+    #[error("mirror-info ticket is not valid base64")]
+    InvalidTicketBase64,
+}
+
+/// Errors returned by [`TicketSealer`](crate::TicketSealer).
+#[derive(Debug, Error)]
+pub enum TicketError {
+    /// The sealed ticket was shorter than the prepended nonce
+    /// ([`NONCE_LEN`](crate::NONCE_LEN), 12 bytes) plus the AEAD tag
+    /// ([`TAG_LEN`](crate::TAG_LEN), 16 bytes), so it cannot possibly be a
+    /// valid ticket.
+    #[error("sealed ticket too short: {0} bytes, need at least 28")]
+    TooShort(usize),
+
+    /// AEAD decryption failed: the ticket, tag, key, or associated data
+    /// (`aad`) did not match.
+    #[error("ticket authentication failed")]
+    AuthenticationFailed,
+}

crates/tlog_mirror/src/lib.rs

@@ -0,0 +1,29 @@
+// Copyright (c) 2025-2026 Cloudflare, Inc. All rights reserved.
+// SPDX-License-Identifier: BSD-3-Clause
+
+//! An implementation of [c2sp.org/tlog-mirror](https://c2sp.org/tlog-mirror).
+//!
+//! Wire-format pieces for building a tlog mirror, scoped to spec-level
+//! concerns:
+//!
+//! * [`wire::AddEntriesRequestHeader`] and [`wire::EntryPackage`] for the
+//!   `add-entries` request body.
+//! * [`wire::MirrorInfo`] for the `text/x.tlog.mirror-info` 409 Conflict
+//!   response body.
+//! * [`TicketSealer`] for the default opaque-ticket scheme.
+//!
+//! A mirror's `add-checkpoint` endpoint is expected to reuse the witness
+//! wire format via the `tlog_witness` crate. Storage, retention, and
+//! pruning policy are out of scope.
+
+pub mod ticket;
+pub mod wire;
+
+mod error;
+
+pub use error::{ParseError, TicketError};
+pub use ticket::{NONCE_LEN, TAG_LEN, TicketSealer};
+pub use wire::{
+    AddEntriesRequestHeader, EntryPackage, MAX_HASHES_PER_PROOF, MIRROR_INFO_CONTENT_TYPE,
+    MirrorInfo, PACKAGE_ALIGNMENT, PackageRanges, package_ranges,
+};