(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);