From 66fb09d98c688744266b4fbe329e27cdf2cb3c41 Mon Sep 17 00:00:00 2001
From: David Drysdale <drysdale@google.com>
Date: Tue, 4 Nov 2025 15:34:58 +0000
Subject: [PATCH 1/2] Move MSRV to 1.81

1.81 is the Rust version that includes `core::error::Error`, released
2024-09-05.
---
 .github/workflows/ci.yml | 2 +-
 Cargo.lock               | 2 +-
 Cargo.toml               | 1 +
 README.md                | 2 +-
 4 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index cb10811..ace4a39 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -93,7 +93,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [1.58.0, 1.59.0]
+        rust: [1.81.0, 1.82.0]
     steps:
       - uses: actions/checkout@8e5e7e5ab8b370d6c329ec480221332ada57f0ab # v3.5.2
         with:
diff --git a/Cargo.lock b/Cargo.lock
index 3fe2a01..9c1283c 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1,6 +1,6 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
-version = 3
+version = 4
 
 [[package]]
 name = "ciborium"
diff --git a/Cargo.toml b/Cargo.toml
index 1ce175c..fe72a00 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -8,6 +8,7 @@ description = "Set of types for supporting COSE"
 repository = "https://github.com/google/coset"
 keywords = ["cryptography", "cose"]
 categories = ["cryptography"]
+rust-version = "1.81"
 
 [features]
 default = []
diff --git a/README.md b/README.md
index 5fb69b6..7cdbe6a 100644
--- a/README.md
+++ b/README.md
@@ -23,7 +23,7 @@ This crate supports `no_std` (when the `std` feature is not set, which is the de
 
 ## Minimum Supported Rust Version
 
-MSRV is 1.58.
+MSRV is 1.81.
 
 ## Integer Ranges
 

From c21a25dd743fe4bc9ea7be8876603a1106b01308 Mon Sep 17 00:00:00 2001
From: David Drysdale <drysdale@google.com>
Date: Tue, 4 Nov 2025 15:26:40 +0000
Subject: [PATCH 2/2] Move to use core version of Error

Also removes the `std` feature.
---
 Cargo.lock        | 2 +-
 Cargo.toml        | 7 +++++--
 README.md         | 4 +++-
 src/common/mod.rs | 3 +--
 src/lib.rs        | 2 +-
 src/util/mod.rs   | 1 -
 6 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 9c1283c..c484aaf 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -31,7 +31,7 @@ dependencies = [
 
 [[package]]
 name = "coset"
-version = "0.4.0"
+version = "0.4.1"
 dependencies = [
  "ciborium",
  "ciborium-io",
diff --git a/Cargo.toml b/Cargo.toml
index fe72a00..7df7c90 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "coset"
-version = "0.4.0"
+version = "0.4.1"
 authors = ["David Drysdale <drysdale@google.com>", "Paul Crowley <paulcrowley@google.com>"]
 edition = "2018"
 license = "Apache-2.0"
@@ -12,7 +12,10 @@ rust-version = "1.81"
 
 [features]
 default = []
-# `std` feature enables an `Error` impl for `CoseError`
+
+# The `std` feature is maintained for back-compatibility; it previously enabled a
+# `std::error::Error` impl for `CoseError`, but the code now (always) has a
+# `core::error::Error` impl.
 std = []
 
 [dependencies]
diff --git a/README.md b/README.md
index 7cdbe6a..54994aa 100644
--- a/README.md
+++ b/README.md
@@ -15,7 +15,9 @@ example](examples/signature.rs) for documentation on how to use the code.
 
 ## Features
 
-The `std` feature of the crate enables an implementation of `std::error::Error` for `CoseError`.
+The `std` feature of the crate does nothing, and is maintained for back-compatibility.  (It previously
+enabled an implementation of `std::error::Error` for `CoseError`, but there is now an implementation
+of `core::error::Error` that is always present.)
 
 ## `no_std` Support
 
diff --git a/src/common/mod.rs b/src/common/mod.rs
index b2c6b78..3d9c630 100644
--- a/src/common/mod.rs
+++ b/src/common/mod.rs
@@ -95,8 +95,7 @@ impl core::fmt::Display for CoseError {
     }
 }
 
-#[cfg(feature = "std")]
-impl std::error::Error for CoseError {}
+impl core::error::Error for CoseError {}
 
 impl CoseError {
     fn fmt_msg(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
diff --git a/src/lib.rs b/src/lib.rs
index 1d1eed5..4ce9c93 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -96,7 +96,7 @@
 //! [COSE]: https://tools.ietf.org/html/rfc8152
 //! [CBOR]: https://tools.ietf.org/html/rfc7049
 
-#![cfg_attr(not(feature = "std"), no_std)]
+#![no_std]
 #![deny(rustdoc::broken_intra_doc_links)]
 extern crate alloc;
 
diff --git a/src/util/mod.rs b/src/util/mod.rs
index 6da9bf4..79d6b1a 100644
--- a/src/util/mod.rs
+++ b/src/util/mod.rs
@@ -164,7 +164,6 @@ pub fn expect_err<T: core::fmt::Debug, E: core::fmt::Debug + core::fmt::Display>
     result: Result<T, E>,
     err_msg: &str,
 ) {
-    #[cfg(not(feature = "std"))]
     use alloc::format;
     match result {
         Ok(_) => {