(1) Change wv_cas_ecm to allow 16 bytes of content_iv

(2) Remove "wrapping_iv" parameters from wv_cas_ecm
(3) Internally derive "wrapping_iv"s and "key_id"s
(4) Add an example binary for demo the usage of wv_cas_ecm

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=218209010

common/crypto_util.cc

@@ -30,6 +30,9 @@ const size_t kSigningKeySizeBytes = 32;
 const char kIvMasterKey[] = "1234567890123456";
 const char kIvLabel[] = "IV_ENCRYPTION";
 const int kIvSizeBits = 128;
+const char kKeyIdMasterKey[] = "0123456789abcdef";
+const char kKeyIdLabel[] = "KEY_ID_ENCRYPTION";
+const int kKeyIdSizeBits = 128;
 const char kGroupKeyLabel[] = "GROUP_ENCRYPTION";
 // TODO(user): This is a temporary key for development. Replace this with
 // a real group master key in keystore.
@@ -137,6 +140,11 @@ std::string DeriveIv(absl::string_view context) {
   return DeriveKey(kIvMasterKey, kIvLabel, context, kIvSizeBits);
 }
 
+// Derives a key ID from the provided info.
+std::string DeriveKeyId(absl::string_view context) {
+  return DeriveKey(kKeyIdMasterKey, kKeyIdLabel, context, kKeyIdSizeBits);
+}
+
 std::string DeriveGroupSessionKey(absl::string_view context,
                              const uint32_t size_bits) {
   return DeriveKey(kPhonyGroupMasterKey, kGroupKeyLabel, context, size_bits);

common/crypto_util.h

@@ -49,6 +49,9 @@ std::string DeriveKey(absl::string_view key, absl::string_view label,
 // Derives an IV from the provided |context|.
 std::string DeriveIv(absl::string_view context);
 
+// Derives a key ID from the provided |context|.
+std::string DeriveKeyId(absl::string_view context);
+
 // Helper function to derive a key using the group master key and context.
 std::string DeriveGroupSessionKey(absl::string_view context, const uint32_t size_bits);
 

common/crypto_util_test.cc

@@ -198,6 +198,21 @@ TEST(CryptoUtilTest, DeriveIv) {
   }
 }
 
+TEST(CryptoUtilTest, DeriveKeyId) {
+  // First value in the pair is the context, second value is the expected id.
+  std::pair<std::string, std::string> context_id_pairs[] = {
+      {"1234567890123456", "a3c4a8c0d0e24e96f38f492254186a9d"},
+      {"0987654321098765", "084fc6bece9688ccce6b1672d9b47e22"}};
+  for (const auto& context_id_pair : context_id_pairs) {
+    SCOPED_TRACE(absl::StrCat("test case:", context_id_pair.first));
+    EXPECT_EQ(context_id_pair.second,
+              absl::BytesToHexString(DeriveKeyId(context_id_pair.first)));
+    // Repeat same call to verify derivied result is repeatable.
+    EXPECT_EQ(context_id_pair.second,
+              absl::BytesToHexString(DeriveKeyId(context_id_pair.first)));
+  }
+}
+
 TEST(CryptoUtilTest, Verify4CCEncryptionIDFromBadString) {
   uint32_t cc_code;
   ASSERT_FALSE(FourCCEncryptionSchemeIDFromString("garbage", &cc_code));