Fix AES corrupt padding test

The AesEcbPkcs7PaddingCorrupted test has been incorrect since it was
originally introduced -- it was feeding the original message as input to
the decryption operation, rather than the corrupted ciphertext.  As a
result, the expected error code was also wrong -- INVALID_INPUT_LENGTH
is appropriate for a too-short cipher text (length 1 in this case),
whereas a corrupt-but-correct-length cipher text should give
INVALID_ARGUMENT.

Fix the test, and add a separate test to cover what was inadvertently
being tested before. Add a sentence to the HAL spec to describe what
expected and tested by CTS/VTS.

Bug: 194126736
Test: VtsAidlKeyMintTargetTest, VtsHalKeymasterV4_0TargetTest
Change-Id: Iaa5e42768814197f373797831093cf344d342b77

1 files changed, 30 insertions, 3 deletions

diff --git a/security/keymint/aidl/vts/functional/KeyMintTest.cpp b/security/keymint/aidl/vts/functional/KeyMintTest.cpp
index 3b75c50acd..384c13542b 100644
--- a/security/keymint/aidl/vts/functional/KeyMintTest.cpp
+++ b/security/keymint/aidl/vts/functional/KeyMintTest.cpp
@@ -5481,18 +5481,45 @@ TEST_P(EncryptionOperationsTest, AesEcbPkcs7PaddingCorrupted) {
 
         EXPECT_EQ(ErrorCode::OK, Begin(KeyPurpose::DECRYPT, params));
         string plaintext;
-        ErrorCode error = Finish(message, &plaintext);
-        if (error == ErrorCode::INVALID_INPUT_LENGTH) {
+        ErrorCode error = Finish(ciphertext, &plaintext);
+        if (error == ErrorCode::INVALID_ARGUMENT) {
             // This is the expected error, we can exit the test now.
             return;
         } else {
             // Very small chance we got valid decryption, so try again.
-            ASSERT_EQ(error, ErrorCode::OK);
+            ASSERT_EQ(error, ErrorCode::OK)
+                    << "Expected INVALID_ARGUMENT or (rarely) OK, got " << error;
         }
     }
     FAIL() << "Corrupt ciphertext should have failed to decrypt by now.";
 }
 
+/*
+ * EncryptionOperationsTest.AesEcbPkcs7CiphertextTooShort
+ *
+ * Verifies that AES decryption fails in the correct way when the padding is corrupted.
+ */
+TEST_P(EncryptionOperationsTest, AesEcbPkcs7CiphertextTooShort) {
+    ASSERT_EQ(ErrorCode::OK, GenerateKey(AuthorizationSetBuilder()
+                                                 .Authorization(TAG_NO_AUTH_REQUIRED)
+                                                 .AesEncryptionKey(128)
+                                                 .Authorization(TAG_BLOCK_MODE, BlockMode::ECB)
+                                                 .Padding(PaddingMode::PKCS7)));
+
+    auto params = AuthorizationSetBuilder().BlockMode(BlockMode::ECB).Padding(PaddingMode::PKCS7);
+
+    string message = "a";
+    string ciphertext = EncryptMessage(message, params);
+    EXPECT_EQ(16U, ciphertext.size());
+    EXPECT_NE(ciphertext, message);
+
+    // Shorten the ciphertext.
+    ciphertext.resize(ciphertext.size() - 1);
+    EXPECT_EQ(ErrorCode::OK, Begin(KeyPurpose::DECRYPT, params));
+    string plaintext;
+    EXPECT_EQ(ErrorCode::INVALID_INPUT_LENGTH, Finish(ciphertext, &plaintext));
+}
+
 vector<uint8_t> CopyIv(const AuthorizationSet& set) {
     auto iv = set.GetTagValue(TAG_NONCE);
     EXPECT_TRUE(iv);