ML-KEM: Fix missing check for SubjectPublicKeyInfo size

Author: vcsjones

src/libraries/Common/src/System/Security/Cryptography/MLKem.cs

@@ -1316,7 +1316,14 @@ public static MLKem ImportSubjectPublicKeyInfo(ReadOnlySpan<byte> source)
                         AsnValueReader reader = new(source, AsnEncodingRules.DER);
                         SubjectPublicKeyInfoAsn.Decode(ref reader, manager.Memory, out SubjectPublicKeyInfoAsn spki);
                         MLKemAlgorithm algorithm = GetAlgorithmIdentifier(ref spki.Algorithm);
-                        return MLKemImplementation.ImportEncapsulationKeyImpl(algorithm, spki.SubjectPublicKey.Span);
+                        ReadOnlySpan<byte> subjectPublicKey = spki.SubjectPublicKey.Span;
+
+                        if (subjectPublicKey.Length != algorithm.EncapsulationKeySizeInBytes)
+                        {
+                            throw new CryptographicException(SR.Argument_KemInvalidEncapsulationKeyLength);
+                        }
+
+                        return MLKemImplementation.ImportEncapsulationKeyImpl(algorithm, subjectPublicKey);
                     }
                 }
             }

src/libraries/Common/tests/System/Security/Cryptography/MLKemTests.cs

@@ -164,6 +164,56 @@ public static void ImportSubjectPublicKeyInfo_NullSource()
                 MLKem.ImportSubjectPublicKeyInfo((byte[])null));
         }
 
+        [Fact]
+        public static void ImportSubjectPublicKeyInfo_WrongAlgorithm()
+        {
+            byte[] ecP256Spki = Convert.FromBase64String(@"
+                MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEuiPJ2IV089LVrXZGDo9Mc542UZZE
+                UtPQVd60Ckb/u5OXHAlmITVzFPThKI+N/bUMEnnHEmF8ZDUtLiQPBaKiMQ==");
+            Assert.Throws<CryptographicException>(() => MLKem.ImportSubjectPublicKeyInfo(ecP256Spki));
+        }
+
+        [Fact]
+        public static void ImportSubjectPublicKeyInfo_WrongParameters()
+        {
+            byte[] mlKem512BadParameters = (
+                "30820342301B0609608648016503040401040E62616420706172616D65746572" +
+                "730382032100002645126709F87B5C6DF9116BA175020895C5C3031AFBBFCDF9" +
+                "5AF2839095396A21F23BB1232091EB8F983BCBC95400D4A335C555187FC2311B" +
+                "79402A261AEB276F1DE4CA62458D5AA772F0C25C3A4824DC095AB63584CF863C" +
+                "D4DCA9736CAAFADC1CA2249475946B4BF4B208334EC419C916157E84C9056DE7" +
+                "13CD055D69009D295C1C1A6A07E008297BD1B167D4641ED946E0432CDD285A5E" +
+                "9794E6D3CF7422012999AC50C42CACC68E659C37CDD93A70166192719CC0E22D" +
+                "1317C1A3F00715004D505A2B606055626421611BCC64425D2F1452E32B8D68B2" +
+                "584A66180D648B8925467DB306DFC39859EAC383AB60B1F9793051C8AE215162" +
+                "1166B3F862B52C44CD796602C80F45D3C095749EA9D65EB6024752761B364891" +
+                "C7669441E3AE30E43178D13B2D1C3B3AFC999FD4B444E3591320A766ACCA6C40" +
+                "59B8F34289211F82C5A333EA029154C716B640AAC1BC7D516DFB00881EFA9472" +
+                "725A9BC57DD1781E7A0689C5E399CB1B1F41A031D33C3528D421047A48A29C91" +
+                "222074FCC538814242C78520D201171615518D36CC98BC885F2127CE182BA150" +
+                "41B07737A8ABA7ACC4C0A22624D49C4854674A54F11AFFB03D7AE6B90E7413B8" +
+                "54A131A6496D02744A66BA7E4B8DF973577EA902E7D1B7CA40CA7AA63F2C04B5" +
+                "D6DA87A735148F003F78395010B11AC9C87E1AB7BDCD8B18CEBA7226E6899DD3" +
+                "A7F2937686D52F7BA21D1A439A7DA06B367C240F644058C434337880FFE79DE9" +
+                "F2A277B13B0B82907E22104F0134423A3F06167FF8254276922361C0368CBC73" +
+                "BFB8C35CD1C0A79076C420B053E604C7098C74344F9A5094983B17ADD46C3498" +
+                "4CA317CDED2B0A1ECC12C52124655389FDB813DBBA8B04310259F0A9EE57B03A" +
+                "B04B18079ABFA336FFF854DA70BD82760A39FB3D9BB2837DF052E925449C8868" +
+                "0242B73A39AB9D332A9C0371CD06663FC6A65968CA27663E44984B91C8B51A2C" +
+                "B0B6364CCE2097DB286E01FB8D2C871472C68117EA6497196F5F56A3CE778D48" +
+                "B687DAF440BB483748B7C2F0889F02DAB06EC64F33E59E49931A20084C7E7856" +
+                "3A766B5223909DC385C5BC4BD8AFF51B5CC52F60FD181D8AC43537254ABC2F29" +
+                "E8FCB8698CD4").HexToByteArray();
+            Assert.Throws<CryptographicException>(() => MLKem.ImportSubjectPublicKeyInfo(mlKem512BadParameters));
+        }
+
+        [Fact]
+        public static void ImportSubjectPublicKeyInfo_WrongSize()
+        {
+            byte[] mlKem512BadEncapKey = "3014300B060960864801650304040103050000264512".HexToByteArray();
+            Assert.Throws<CryptographicException>(() => MLKem.ImportSubjectPublicKeyInfo(mlKem512BadEncapKey));
+        }
+
         [Fact]
         public static void ImportPkcs8PrivateKey_NullSource()
         {