KeyMint VTS: ATTEST_KEY has no other purpose

The KeyMint spec has always required that keys with the ATTEST_KEY
purpose "must not have any other purpose".

Add explicit tests for combined-purpose keys to be rejected.

Also expand the spec text to require a specific error code, and to
explain the rationale for single-purpose ATTEST_KEY keys.

Bug: 197096139
Test: VtsAidlKeyMintTargetTest
Change-Id: I2a2014f0ddc497128ba51bb3f43671f759789912

1 files changed, 36 insertions, 0 deletions

diff --git a/security/keymint/aidl/vts/functional/KeyMintTest.cpp b/security/keymint/aidl/vts/functional/KeyMintTest.cpp
index 670043d0dd..186873880c 100644
--- a/security/keymint/aidl/vts/functional/KeyMintTest.cpp
+++ b/security/keymint/aidl/vts/functional/KeyMintTest.cpp
@@ -3284,6 +3284,26 @@ TEST_P(ImportKeyTest, RsaPublicExponentMismatch) {
 }
 
 /*
+ * ImportKeyTest.RsaAttestMultiPurposeFail
+ *
+ * Verifies that importing an RSA key pair with purpose ATTEST_KEY+SIGN fails.
+ */
+TEST_P(ImportKeyTest, RsaAttestMultiPurposeFail) {
+    uint32_t key_size = 2048;
+    string key = rsa_2048_key;
+
+    ASSERT_EQ(ErrorCode::INCOMPATIBLE_PURPOSE,
+              ImportKey(AuthorizationSetBuilder()
+                                .Authorization(TAG_NO_AUTH_REQUIRED)
+                                .RsaSigningKey(key_size, 65537)
+                                .AttestKey()
+                                .Digest(Digest::SHA_2_256)
+                                .Padding(PaddingMode::RSA_PSS)
+                                .SetDefaultValidity(),
+                        KeyFormat::PKCS8, key));
+}
+
+/*
  * ImportKeyTest.EcdsaSuccess
  *
  * Verifies that importing and using an ECDSA P-256 key pair works correctly.
@@ -3402,6 +3422,22 @@ TEST_P(ImportKeyTest, EcdsaCurveMismatch) {
 }
 
 /*
+ * ImportKeyTest.EcdsaAttestMultiPurposeFail
+ *
+ * Verifies that importing and using an ECDSA P-256 key pair with purpose ATTEST_KEY+SIGN fails.
+ */
+TEST_P(ImportKeyTest, EcdsaAttestMultiPurposeFail) {
+    ASSERT_EQ(ErrorCode::INCOMPATIBLE_PURPOSE,
+              ImportKey(AuthorizationSetBuilder()
+                                .Authorization(TAG_NO_AUTH_REQUIRED)
+                                .EcdsaSigningKey(EcCurve::P_256)
+                                .AttestKey()
+                                .Digest(Digest::SHA_2_256)
+                                .SetDefaultValidity(),
+                        KeyFormat::PKCS8, ec_256_key));
+}
+
+/*
  * ImportKeyTest.AesSuccess
  *
  * Verifies that importing and using an AES key works.