From c7aa037f3e58b7cf7c42b6f1034de03832f535c1 Mon Sep 17 00:00:00 2001
From: Steven Collison <soco@amazon.com>
Date: Tue, 21 May 2024 13:20:51 -0700
Subject: [PATCH] Add s2n_signature_preferences_20240521

This preference list is to allow ECDSA sigalgs to be prioritized for
policies that need legacy sigalg(SHA1) support.

This change is needed because TLS1.3 is reliant on the sigalg
preferences to drive server certificate preference selection.
---
 tls/s2n_signature_scheme.c | 35 +++++++++++++++++++++++++++++++++++
 tls/s2n_signature_scheme.h |  1 +
 2 files changed, 36 insertions(+)

diff --git a/tls/s2n_signature_scheme.c b/tls/s2n_signature_scheme.c
index f8af64e5d66..5349ff991bd 100644
--- a/tls/s2n_signature_scheme.c
+++ b/tls/s2n_signature_scheme.c
@@ -435,6 +435,41 @@ const struct s2n_signature_preferences s2n_certificate_signature_preferences_rfc
     .signature_schemes = s2n_cert_sig_scheme_pref_list_rfc9151
 };
 
+/*
+ * Legacy compatibility policy based on s2n_sig_scheme_pref_list_20201021 with ECDSA prioritized.
+ * This list also removes ECDSA+SHA224, which is not known to be relied on by any legitimate
+ * use cases.
+ */
+const struct s2n_signature_scheme* const s2n_sig_scheme_pref_list_20240521[] = {
+    /* ECDSA */
+    &s2n_ecdsa_sha256,
+    &s2n_ecdsa_sha384,
+    &s2n_ecdsa_sha512,
+
+    /* RSA PSS */
+    &s2n_rsa_pss_pss_sha256,
+    &s2n_rsa_pss_pss_sha384,
+    &s2n_rsa_pss_pss_sha512,
+    &s2n_rsa_pss_rsae_sha256,
+    &s2n_rsa_pss_rsae_sha384,
+    &s2n_rsa_pss_rsae_sha512,
+
+    /* RSA PKCS1 */
+    &s2n_rsa_pkcs1_sha256,
+    &s2n_rsa_pkcs1_sha384,
+    &s2n_rsa_pkcs1_sha512,
+    &s2n_rsa_pkcs1_sha224,
+
+    /* SHA-1 Legacy */
+    &s2n_rsa_pkcs1_sha1,
+    &s2n_ecdsa_sha1,
+};
+
+const struct s2n_signature_preferences s2n_signature_preferences_20240521 = {
+    .count = s2n_array_len(s2n_sig_scheme_pref_list_20240521),
+    .signature_schemes = s2n_sig_scheme_pref_list_20240521
+};
+
 const struct s2n_signature_scheme* const s2n_sig_scheme_pref_list_test_all_fips[] = {
     /* RSA PSS */
     &s2n_rsa_pss_pss_sha256,
diff --git a/tls/s2n_signature_scheme.h b/tls/s2n_signature_scheme.h
index 8b72d1086db..39d0c239fd4 100644
--- a/tls/s2n_signature_scheme.h
+++ b/tls/s2n_signature_scheme.h
@@ -75,6 +75,7 @@ extern const struct s2n_signature_preferences s2n_signature_preferences_20140601
 extern const struct s2n_signature_preferences s2n_signature_preferences_20200207;
 extern const struct s2n_signature_preferences s2n_signature_preferences_20201021;
 extern const struct s2n_signature_preferences s2n_signature_preferences_20210816;
+extern const struct s2n_signature_preferences s2n_signature_preferences_20240521;
 extern const struct s2n_signature_preferences s2n_signature_preferences_rfc9151;
 extern const struct s2n_signature_preferences s2n_certificate_signature_preferences_rfc9151;
 extern const struct s2n_signature_preferences s2n_signature_preferences_default_fips;