From 9e9127d49e321e42e478933ee00f86232e4ea010 Mon Sep 17 00:00:00 2001
From: Rich Logan <rich@richlogan.co.uk>
Date: Fri, 30 May 2025 08:13:26 +0100
Subject: [PATCH] Add error descriptions

---
 Sources/SFrame/MLS.swift           | 16 ++++++++++++++++
 Sources/SFrame/Provider.swift      |  7 +++++++
 Sources/SFrame/SFrame.swift        | 17 ++++++++++++++++-
 Sources/SFrame/SyntheticAEAD.swift | 13 +++++++++++++
 Sources/SFrame/Utilities.swift     | 15 +++++++++++----
 Tests/SFrameTests/Utilities.swift  | 10 ++++++++++
 6 files changed, 73 insertions(+), 5 deletions(-)

diff --git a/Sources/SFrame/MLS.swift b/Sources/SFrame/MLS.swift
index de95880..607bc81 100644
--- a/Sources/SFrame/MLS.swift
+++ b/Sources/SFrame/MLS.swift
@@ -15,6 +15,22 @@ public enum MLSError: Error {
     case contextOverflow
     /// Epoch bits must be 0 < x < 64.
     case badEpochBits
+
+    public var localizedDescription: String {
+        switch self {
+        case .unknownEpoch:
+            return "Unknown epoch."
+
+        case .senderOverflow:
+            return "Sender ID exceeds maximum allowed."
+
+        case .contextOverflow:
+            return "Context ID exceeds maximum allowed."
+
+        case .badEpochBits:
+            return "Epoch bits must be between 1 and 63."
+        }
+    }
 }
 
 /// Provides an interface to utilize SFrame with MLS keying.
diff --git a/Sources/SFrame/Provider.swift b/Sources/SFrame/Provider.swift
index 51640f3..065a4f6 100644
--- a/Sources/SFrame/Provider.swift
+++ b/Sources/SFrame/Provider.swift
@@ -76,4 +76,11 @@ public protocol CryptoProvider {
 public enum CryptoProviderError: Error {
     /// This provider does not support the requested cipher suite.
     case unsupportedCipherSuite
+
+    public var localizedDescription: String {
+        switch self {
+        case .unsupportedCipherSuite:
+            return "This provider does not support the requested cipher suite."
+        }
+    }
 }
diff --git a/Sources/SFrame/SFrame.swift b/Sources/SFrame/SFrame.swift
index 51b0855..713e2c9 100644
--- a/Sources/SFrame/SFrame.swift
+++ b/Sources/SFrame/SFrame.swift
@@ -17,7 +17,22 @@ public enum SFrameError: Error {
     case existingKey
     case badParameter
     case malformedCipherText
-    case keyMisuse
+
+    public var localizedDescription: String {
+        switch self {
+        case .missingKey:
+            return "The required key is missing."
+
+        case .existingKey:
+            return "This key already exists."
+
+        case .badParameter:
+            return "A bit size parameter was invalid."
+
+        case .malformedCipherText:
+            return "The ciphertext is malformed."
+        }
+    }
 }
 
 /// The operation this key is to be used for.
diff --git a/Sources/SFrame/SyntheticAEAD.swift b/Sources/SFrame/SyntheticAEAD.swift
index 9045f72..c4de2ee 100644
--- a/Sources/SFrame/SyntheticAEAD.swift
+++ b/Sources/SFrame/SyntheticAEAD.swift
@@ -9,6 +9,19 @@ public enum SyntheticAEADError: Error {
     case missingKeySize
     case authenticationFailure
     case badKeySize
+
+    public var localizedDescription: String {
+        switch self {
+        case .missingKeySize:
+            return "The cipher suite does not specify a key size."
+
+        case .authenticationFailure:
+            return "Authentication failed."
+
+        case .badKeySize:
+            return "The provided key size does not match the cipher suite requirements."
+        }
+    }
 }
 
 /// SFrame AES-CTR with SHA2 implementation.
diff --git a/Sources/SFrame/Utilities.swift b/Sources/SFrame/Utilities.swift
index ce37ebe..4406d07 100644
--- a/Sources/SFrame/Utilities.swift
+++ b/Sources/SFrame/Utilities.swift
@@ -4,10 +4,6 @@
 
 import Foundation
 
-public enum DataError: Error {
-    case lengthMismatch
-}
-
 // SealedBox implementation.
 internal struct SealedDataBox: SealedBox {
     internal let authTag: Data
@@ -15,6 +11,17 @@ internal struct SealedDataBox: SealedBox {
     internal let nonceBytes: Data
 }
 
+public enum DataError: Error {
+    case lengthMismatch
+
+    public var localizedDescription: String {
+        switch self {
+        case .lengthMismatch:
+            return "XOR requires buffers of equal length."
+        }
+    }
+}
+
 extension Data {
     /// Initialize a view into a contiguous byte buffer.
     /// - Parameter bytes: The contiguous byte buffer to expose a view into.
diff --git a/Tests/SFrameTests/Utilities.swift b/Tests/SFrameTests/Utilities.swift
index 56d4005..dfb61ba 100644
--- a/Tests/SFrameTests/Utilities.swift
+++ b/Tests/SFrameTests/Utilities.swift
@@ -176,6 +176,16 @@ internal func hexToData(_ hex: String) -> Data {
 internal enum TestError: Error {
     case missingVectors
     case unsupportedCipherSuite
+
+    internal var localizedDescription: String {
+        switch self {
+        case .missingVectors:
+            return "Test vectors are missing."
+
+        case .unsupportedCipherSuite:
+            return "The cipher suite is not supported."
+        }
+    }
 }
 
 internal func loadTestVectors() throws -> TestVectors {