From 89ca965d2a831fe7b515cf83175652db1d0ecdc9 Mon Sep 17 00:00:00 2001
From: Gabriela Moldovan <gabi@torproject.org>
Date: Fri, 17 Mar 2023 20:19:22 +0000
Subject: [PATCH] Define constants for `AuthClient` field lengths.

These are used in multiple places (and will also be used by the HS
descriptor encoder later on), so let's make them named constants.

Signed-off-by: Gabriela Moldovan <gabi@torproject.org>
---
 crates/tor-netdoc/src/doc/hsdesc/desc_enc.rs | 11 ++++++++++-
 crates/tor-netdoc/src/doc/hsdesc/middle.rs   | 15 +++++++++------
 2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/crates/tor-netdoc/src/doc/hsdesc/desc_enc.rs b/crates/tor-netdoc/src/doc/hsdesc/desc_enc.rs
index fe00d505f..89452c6ed 100644
--- a/crates/tor-netdoc/src/doc/hsdesc/desc_enc.rs
+++ b/crates/tor-netdoc/src/doc/hsdesc/desc_enc.rs
@@ -41,13 +41,22 @@ pub(super) struct HsDescEncryption<'a> {
     pub(super) string_const: &'a [u8],
 }
 
+/// The length of a client ID.
+pub(crate) const HS_DESC_MIDDLE_CLIENT_ID_LEN: usize = 8;
+
+/// The length of the the `AuthClient` IV.
+pub(crate) const HS_DESC_MIDDLE_IV_LEN: usize = 16;
+
+/// The length of an `N_hs_desc_enc` nonce (also known as a "descriptor cookie").
+pub(crate) const HS_DESC_MIDDLE_ENC_NONCE_LEN: usize = 16;
+
 /// A value used in deriving the encryption key for the inner (encryption) layer
 /// of onion service encryption.
 ///
 /// This is  `N_hs_desc_enc` in the spec, where sometimes we also call it a
 /// "descriptor cookie".
 #[derive(derive_more::AsRef, derive_more::From)]
-pub(super) struct HsDescEncNonce([u8; 16]);
+pub(super) struct HsDescEncNonce([u8; HS_DESC_MIDDLE_ENC_NONCE_LEN]);
 
 /// Length of our cryptographic salt.
 const SALT_LEN: usize = 16;
diff --git a/crates/tor-netdoc/src/doc/hsdesc/middle.rs b/crates/tor-netdoc/src/doc/hsdesc/middle.rs
index ff9cdb0c5..b3df1ca2c 100644
--- a/crates/tor-netdoc/src/doc/hsdesc/middle.rs
+++ b/crates/tor-netdoc/src/doc/hsdesc/middle.rs
@@ -12,7 +12,10 @@ use crate::parse::{keyword::Keyword, parser::SectionRules};
 use crate::types::misc::B64;
 use crate::{Pos, Result};
 
-use super::desc_enc::{HsDescEncNonce, HsDescEncryption};
+use super::desc_enc::{
+    HsDescEncNonce, HsDescEncryption, HS_DESC_MIDDLE_CLIENT_ID_LEN, HS_DESC_MIDDLE_ENC_NONCE_LEN,
+    HS_DESC_MIDDLE_IV_LEN,
+};
 use super::DecryptionError;
 
 /// A more-or-less verbatim representation of the middle document of an onion
@@ -67,7 +70,7 @@ impl HsDescMiddle {
     }
 
     /// Use a `ClientDescAuthSecretKey` (`KS_hsc_desc_enc`) to see if there is any `auth-client`
-    /// entry for us (a client who holds that secret key) in this descriptor.  
+    /// entry for us (a client who holds that secret key) in this descriptor.
     /// If so, decrypt it and return its
     /// corresponding "Descriptor Cookie" (`N_hs_desc_enc`)
     ///
@@ -135,11 +138,11 @@ struct AuthClient {
     /// A check field that clients can use to see if this [`AuthClient`] entry corresponds to a key they hold.
     ///
     /// This is the first part of the `auth-client` line.
-    client_id: CtByteArray<8>,
+    client_id: CtByteArray<HS_DESC_MIDDLE_CLIENT_ID_LEN>,
     /// An IV used to decrypt `encrypted_cookie`.
     ///
     /// This is the second item on the `auth-client` line.
-    iv: [u8; 16],
+    iv: [u8; HS_DESC_MIDDLE_IV_LEN],
     /// An encrypted value used to find the descriptor cookie `N_hs_desc_enc`,
     /// which in turn is
     /// needed to decrypt the [HsDescMiddle]'s `encrypted_body`.
@@ -147,7 +150,7 @@ struct AuthClient {
     /// This is the third item on the `auth-client` line.  When decrypted, it
     /// reveals a `DescEncEncryptionCookie` (`N_hs_desc_enc`, not yet so named
     /// in the spec).
-    encrypted_cookie: [u8; 16],
+    encrypted_cookie: [u8; HS_DESC_MIDDLE_ENC_NONCE_LEN],
 }
 
 impl AuthClient {
@@ -203,7 +206,7 @@ impl HsDescMiddle {
         Ok(result)
     }
 
-    /// Extract an HsDescMiddle from a reader.  
+    /// Extract an HsDescMiddle from a reader.
     ///
     /// The reader must contain a single HsDescOuter; we return an error if not.
     fn take_from_reader(reader: &mut NetDocReader<'_, HsMiddleKwd>) -> Result<HsDescMiddle> {