From 661631138a14b0c1f2106595a2227543cd1a39a4 Mon Sep 17 00:00:00 2001
From: Vladimir Dubrovin <3proxy@3proxy.ru>
Date: Wed, 26 Aug 2026 16:55:37 +0300
Subject: [PATCH] Give an intercepted certificate its key identifiers

A verifier following RFC 5280 strictly looks for the issuer through a key
identifier and refuses a certificate carrying none: OpenSSL does with
x509_strict, and Python has since 3.13, so a current client rejects an
intercepted connection outright. Working around that by turning verification
off in the client removes the protection interception was meant to preserve.

Generate the identifiers rather than copying them, so they name the CA
signing here and not the one that signed upstream. wolfSSL cannot generate
extensions, so this is in the branch that already depends on that.
---
 src/ssllib.c | 28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/src/ssllib.c b/src/ssllib.c
index 5122e99..f9f5e6c 100644
--- a/src/ssllib.c
+++ b/src/ssllib.c
@@ -84,7 +84,11 @@ static int copy_ext(X509 *dst_cert, X509 *src_cert, int nid)
 }
 
 #ifndef WITH_WOLFSSL
-static int add_ext(X509 *cert, int nid, const char *value)
+/* issuer is the certificate the extension should describe as the issuer,
+ * which matters for an authority key identifier: it names the key that
+ * signs, not the key being signed.
+ */
+static int add_ext_issuer(X509 *cert, X509 *issuer, int nid, const char *value)
 {
 	X509_EXTENSION *ex;
 	X509V3_CTX ctx;
@@ -92,10 +96,8 @@ static int add_ext(X509 *cert, int nid, const char *value)
 	/* This sets the 'context' of the extensions. */
 	/* No configuration database */
 	X509V3_set_ctx_nodb(&ctx);
-	/* Issuer and subject certs: both the target since it is self signed,
-	 * no request and no CRL
-	 */
-	X509V3_set_ctx(&ctx, cert, cert, NULL, NULL, 0);
+	/* No request and no CRL */
+	X509V3_set_ctx(&ctx, issuer, cert, NULL, NULL, 0);
 	/* value is char * prior to OpenSSL 1.1.0 */
 	ex = X509V3_EXT_conf_nid(NULL, &ctx, nid, (char *)value);
 	if (!ex)
@@ -105,6 +107,12 @@ static int add_ext(X509 *cert, int nid, const char *value)
 	X509_EXTENSION_free(ex);
 	return err > 0;
 }
+
+static int add_ext(X509 *cert, int nid, const char *value)
+{
+	/* Issuer and subject: both the target, for a self signed certificate */
+	return add_ext_issuer(cert, cert, nid, value);
+}
 #endif
 
 SSL_CERT ssl_copy_cert(SSL_CERT cert, SSL_CONFIG *config)
@@ -199,6 +207,16 @@ SSL_CERT ssl_copy_cert(SSL_CERT cert, SSL_CONFIG *config)
 		add_ext(dst_cert, NID_basic_constraints, "critical,CA:FALSE");
 	if(!copy_ext(dst_cert, src_cert, NID_ext_key_usage))
 		add_ext(dst_cert, NID_ext_key_usage, "serverAuth");
+	/* A verifier following RFC 5280 strictly looks for the issuer through a
+	 * key identifier and refuses a certificate carrying none: OpenSSL does
+	 * with x509_strict, and Python has since 3.13. The identifiers are
+	 * generated rather than copied, so they name the CA signing here
+	 * instead of the one that signed upstream. keyid,issuer keeps working
+	 * when the CA certificate has no subject key identifier of its own.
+	 */
+	add_ext(dst_cert, NID_subject_key_identifier, "hash");
+	add_ext_issuer(dst_cert, config->CA_cert, NID_authority_key_identifier,
+		"keyid,issuer");
 #else
 	copy_ext(dst_cert, src_cert, NID_basic_constraints);
 	copy_ext(dst_cert, src_cert, NID_ext_key_usage);