allow SPKI RSA keys to be parsed even if they have an incorrect delimiter

docs/development/test-vectors.rst

@@ -78,6 +78,9 @@ Custom asymmetric vectors
 * ``asymmetric/PEM_Serialization/rsa_public_key.pem`` and
   ``asymmetric/DER_Serialization/rsa_public_key.der``- Contains an RSA 2048
   bit public generated using OpenSSL from ``rsa_private_key.pem``.
+* ``asymmetric/PEM_Serialization/rsa_wrong_delimiter_public_key.pem`` - Contains
+  an RSA 2048 bit public key generated from ``rsa_private_key.pem``, but with
+  the wrong PEM delimiter (``RSA PUBLIC KEY`` when it should be ``PUBLIC KEY``).
 * ``asymmetric/PEM_Serialization/dsa_4096.pem`` - Contains a 4096-bit DSA
   private key generated using OpenSSL.
 * ``asymmetric/PEM_Serialization/dsaparam.pem`` - Contains 2048-bit DSA

src/rust/src/backend/keys.rs

@@ -165,7 +165,15 @@ fn load_pem_public_key(
     let _ = backend;
     let p = pem::parse(data.as_bytes())?;
     let pkey = match p.tag() {
-        "RSA PUBLIC KEY" => cryptography_key_parsing::rsa::parse_pkcs1_public_key(p.contents())?,
+        "RSA PUBLIC KEY" => {
+            // We try to parse it as a PKCS1 first since that's the PEM delimiter, and if
+            // that fails we try to parse it as an SPKI. This is to match the permissiveness
+            // of OpenSSL, which doesn't care about the delimiter.
+            match cryptography_key_parsing::rsa::parse_pkcs1_public_key(p.contents()) {
+                Ok(pkey) => pkey,
+                Err(_) => cryptography_key_parsing::spki::parse_public_key(p.contents())?,
+            }
+        }
         "PUBLIC KEY" => cryptography_key_parsing::spki::parse_public_key(p.contents())?,
         _ => return Err(CryptographyError::from(pem::PemError::MalformedFraming)),
     };

tests/hazmat/primitives/test_serialization.py

@@ -506,6 +506,11 @@ def test_load_pem_ec_private_key(self, key_path, password, backend):
                 "asymmetric", "PEM_Serialization", "rsa_public_key.pem"
             ),
             os.path.join("asymmetric", "public", "PKCS1", "rsa.pub.pem"),
+            os.path.join(
+                "asymmetric",
+                "PEM_Serialization",
+                "rsa_wrong_delimiter_public_key.pem",
+            ),
         ],
     )
     def test_load_pem_rsa_public_key(self, key_file, backend):

vectors/cryptography_vectors/asymmetric/PEM_Serialization/rsa_wrong_delimiter_public_key.pem

@@ -0,0 +1,9 @@
+-----BEGIN RSA PUBLIC KEY-----
+MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAnR4AZ+tgWYql+S3MaTQ6
+zeIO1fKzFIoau9Q0zGuv/1oCAewXwxeDSSxw+/Z3GL1NpuuS9CpbR5EQ3d71bD0v
+0G+Sf+mShSl0oljG7YqnNSPzKl+EQ3/KE+eEButcwas6KGof2BA4bFNCw/fPbuhk
+u/d8sIIEgdzBMiGRMdW33uci3rsdOenMZQA7uWsM/q/pu85YLAVOxq6wlUCzP4FM
+Tw/RKzayrPkn3Jfbqcy1aM2HDlFVx24vaN+RRbPSnVoQbo5EQYkUMXE8WmadSyHl
+pXGRnWsJSV9AdGyDrbU+6tcFwcIwnW22jb/OJy8swHdqKGkuR1kQ0XqokK1yGKFZ
+8wIDAQAB
+-----END RSA PUBLIC KEY-----