Add Linux support for PKCS#1 RSA public keys (#135)

Motivation

The init(derRepresentation:) and init(pemRepresentation:) constructors
for RSA public keys support both PKCS#8 and PKCS#1 key formats on
Darwin. This support was missing from Linux, with only PKCS#8 support.
This patch brings the two platforms into parity.

Modifications

Add code to try both versions on Linux.
Add tests.

Results

PKCS#1 keys are supported on Linux too!

Sources/_CryptoExtras/RSA/RSA_boring.swift

@@ -106,13 +106,26 @@ extension BoringSSLRSAPublicKey {
         fileprivate init(pemRepresentation: String) throws {
             var pemRepresentation = pemRepresentation
 
-            self.pointer = try pemRepresentation.withUTF8 { utf8Ptr in
-                return try BIOHelper.withReadOnlyMemoryBIO(wrapping: utf8Ptr) { bio in
-                    guard let key = CCryptoBoringSSL_PEM_read_bio_RSA_PUBKEY(bio, nil, nil, nil) else {
-                        throw CryptoKitError.internalBoringSSLError()
+            // There are two encodings for RSA public keys: PKCS#1 and the SPKI form.
+            // The SPKI form is what we support for EC keys, so we try that first, then we
+            // fall back to the PKCS#1 form if that parse fails.
+            do {
+                self.pointer = try pemRepresentation.withUTF8 { utf8Ptr in
+                    return try BIOHelper.withReadOnlyMemoryBIO(wrapping: utf8Ptr) { bio in
+                        guard let key = CCryptoBoringSSL_PEM_read_bio_RSA_PUBKEY(bio, nil, nil, nil) else {
+                            throw CryptoKitError.internalBoringSSLError()
+                        }
+                        return key
+                    }
+                }
+            } catch {
+                self.pointer = try pemRepresentation.withUTF8 { utf8Ptr in
+                    return try BIOHelper.withReadOnlyMemoryBIO(wrapping: utf8Ptr) { bio in
+                        guard let key = CCryptoBoringSSL_PEM_read_bio_RSAPublicKey(bio, nil, nil, nil) else {
+                            throw CryptoKitError.internalBoringSSLError()
+                        }
+                        return key
                     }
-
-                    return key
                 }
             }
         }
@@ -127,12 +140,26 @@ extension BoringSSLRSAPublicKey {
         }
 
         private init<Bytes: ContiguousBytes>(contiguousDerRepresentation: Bytes) throws {
-            self.pointer = try contiguousDerRepresentation.withUnsafeBytes { derPtr in
-                return try BIOHelper.withReadOnlyMemoryBIO(wrapping: derPtr) { bio in
-                    guard let key = CCryptoBoringSSL_d2i_RSA_PUBKEY_bio(bio, nil) else {
-                        throw CryptoKitError.internalBoringSSLError()
+            // There are two encodings for RSA public keys: PKCS#1 and the SPKI form.
+            // The SPKI form is what we support for EC keys, so we try that first, then we
+            // fall back to the PKCS#1 form if that parse fails.
+            do {
+                self.pointer = try contiguousDerRepresentation.withUnsafeBytes { derPtr in
+                    return try BIOHelper.withReadOnlyMemoryBIO(wrapping: derPtr) { bio in
+                        guard let key = CCryptoBoringSSL_d2i_RSA_PUBKEY_bio(bio, nil) else {
+                            throw CryptoKitError.internalBoringSSLError()
+                        }
+                        return key
+                    }
+                }
+            } catch {
+                self.pointer = try contiguousDerRepresentation.withUnsafeBytes { derPtr in
+                    return try BIOHelper.withReadOnlyMemoryBIO(wrapping: derPtr) { bio in
+                        guard let key = CCryptoBoringSSL_d2i_RSAPublicKey_bio(bio, nil) else {
+                            throw CryptoKitError.internalBoringSSLError()
+                        }
+                        return key
                     }
-                    return key
                 }
             }
         }

Tests/_CryptoExtrasTests/TestRSASigning.swift

@@ -569,6 +569,43 @@ final class TestRSASigning: XCTestCase {
         XCTAssertThrowsError(try _RSA.Signing.PrivateKey(keySize: .init(bitCount: 1016)))
     }
 
+    func testParsingPKCS1PublicKeyKeyDER() throws {
+        let pkcs1Key = Data(base64Encoded:
+            "MIICCgKCAgEAkehUktIKVrGsDSTdxc9EZ3SZKzejfSNwAHG8U9/E+ioSj0t" +
+            "/EFa9n3Byt2F/yUsPF6c947AEYe7/EZfH9IY+Cvo+XPmT5jR62RRr55yzha" +
+            "CCenavcZDX7P0N+pxs+t+wgvQUfvm+xKYvT3+Zf7X8Z0NyvQwA1onrayzT7" +
+            "Y+YHBSrfuXjbvzYqOSSJNpDa2K4Vf3qwbxstovzDo2a5JtsaZn4eEgwRdWt" +
+            "4Q08RWD8MpZRJ7xnw8outmvqRsfHIKCxH2XeSAi6pE6p8oNGN4Tr6MyBSEN" +
+            "nTnIqm1y9TBsoilwie7SrmNnu4FGDwwlGTm0+mfqVF9p8M1dBPI1R7Qu2XK" +
+            "8sYxrfV8g/vOldxJuvRZnio1oktLqpVj3Pb6r/SVi+8Kj/9Lit6Tf7urj0C" +
+            "zr56ENCHonYhMsT8dm74YlguIwoVqwUHZwK53Hrzw7dPamWoUi9PPevtQ0i" +
+            "TMARgexWO/bTouJbt7IEIlKVgJNp6I5MZfGRAy1wdALqi2cVKWlSArvX31B" +
+            "qVUa/oKMoYX9w0MOiqiwhqkfOKJwGRXa/ghgntNWutMtQ5mv0TIZxMOmm3x" +
+            "aG4Nj/QN370EKIf6MzOi5cHkERgWPOGHFrK+ymircxXDpqR+DDeVnWIBqv8" +
+            "mqYqnK8V0rSS527EPywTEHl7R09XiidnMy/s1Hap0flhFMCAwEAAQ=="
+        )!
+        XCTAssertNoThrow(try _RSA.Signing.PublicKey(derRepresentation: pkcs1Key))
+    }
+
+    func testParsingPKCS1PublicKeyKeyPEM() throws {
+        let pemKey = """
+        -----BEGIN RSA PUBLIC KEY-----
+        MIICCgKCAgEAkehUktIKVrGsDSTdxc9EZ3SZKzejfSNwAHG8U9/E+ioSj0t/EFa9
+        n3Byt2F/yUsPF6c947AEYe7/EZfH9IY+Cvo+XPmT5jR62RRr55yzhaCCenavcZDX
+        7P0N+pxs+t+wgvQUfvm+xKYvT3+Zf7X8Z0NyvQwA1onrayzT7Y+YHBSrfuXjbvzY
+        qOSSJNpDa2K4Vf3qwbxstovzDo2a5JtsaZn4eEgwRdWt4Q08RWD8MpZRJ7xnw8ou
+        tmvqRsfHIKCxH2XeSAi6pE6p8oNGN4Tr6MyBSENnTnIqm1y9TBsoilwie7SrmNnu
+        4FGDwwlGTm0+mfqVF9p8M1dBPI1R7Qu2XK8sYxrfV8g/vOldxJuvRZnio1oktLqp
+        Vj3Pb6r/SVi+8Kj/9Lit6Tf7urj0Czr56ENCHonYhMsT8dm74YlguIwoVqwUHZwK
+        53Hrzw7dPamWoUi9PPevtQ0iTMARgexWO/bTouJbt7IEIlKVgJNp6I5MZfGRAy1w
+        dALqi2cVKWlSArvX31BqVUa/oKMoYX9w0MOiqiwhqkfOKJwGRXa/ghgntNWutMtQ
+        5mv0TIZxMOmm3xaG4Nj/QN370EKIf6MzOi5cHkERgWPOGHFrK+ymircxXDpqR+DD
+        eVnWIBqv8mqYqnK8V0rSS527EPywTEHl7R09XiidnMy/s1Hap0flhFMCAwEAAQ==
+        -----END RSA PUBLIC KEY-----
+        """
+        XCTAssertNoThrow(try _RSA.Signing.PublicKey(pemRepresentation: pemKey))
+    }
+
     private func testPKCS1Group(_ group: RSAPKCS1TestGroup) throws {
         let derKey = try _RSA.Signing.PublicKey(derRepresentation: group.keyDerBytes)
         let pemKey = try _RSA.Signing.PublicKey(pemRepresentation: group.keyPem)