Add utility for generating KDF contexts

Starting in v19, OEMCrypto implementers will need to implement KDF generation in OEMCrypto.  To make it easier, this adds a utility to generate them based on the request context.

PiperOrigin-RevId: 572693987
Change-Id: Ife382bf35ceede508499e3677de115ef12999dcc

libwvdrmengine/oemcrypto/odk/src/odk.c

@@ -9,6 +9,7 @@
 #include <stdio.h>
 #include <string.h>
 
+#include "OEMCryptoCENCCommon.h"
 #include "odk_message.h"
 #include "odk_overflow.h"
 #include "odk_serialize.h"
@@ -589,3 +590,69 @@ bool CheckApiVersionAtMost(const ODK_NonceValues* nonce_values,
          (nonce_values->api_major_version == major_version &&
           nonce_values->api_minor_version <= minor_version);
 }
+
+const uint8_t ODK_MacKeyLabelWithZero[] = "AUTHENTICATION";
+const size_t ODK_MacKeyLabelWithZeroLength = sizeof(ODK_MacKeyLabelWithZero);
+// This is the key size (512) in network byte order.
+const uint8_t ODK_MacKeySuffix[] = {0x00, 0x00, 0x02, 0x00};
+const size_t ODK_MacKeySuffixLength = sizeof(ODK_MacKeySuffix);
+
+const uint8_t ODK_EncKeyLabelWithZero[] = "ENCRYPTION";
+const size_t ODK_EncKeyLabelWithZeroLength = sizeof(ODK_EncKeyLabelWithZero);
+// This is the key size (128) in network byte order.
+const uint8_t ODK_EncKeySuffix[] = {0x00, 0x00, 0x00, 0x80};
+const size_t ODK_EncKeySuffixLength = sizeof(ODK_EncKeySuffix);
+
+OEMCryptoResult ODK_GenerateKeyContexts(const uint8_t* context,
+                                        size_t context_length,
+                                        uint8_t* mac_key_context,
+                                        size_t* mac_key_context_length,
+                                        uint8_t* enc_key_context,
+                                        size_t* enc_key_context_length) {
+  size_t real_mac_length;
+  size_t real_enc_length;
+  if (odk_add_overflow_ux(
+          context_length,
+          ODK_MacKeyLabelWithZeroLength + ODK_MacKeySuffixLength,
+          &real_mac_length) ||
+      real_mac_length > 0xffffffff ||
+      odk_add_overflow_ux(
+          context_length,
+          ODK_EncKeyLabelWithZeroLength + ODK_EncKeySuffixLength,
+          &real_enc_length) ||
+      real_enc_length > 0xffffffff) {
+    return OEMCrypto_ERROR_INVALID_CONTEXT;
+  }
+  bool short_buffer = false;
+  if (mac_key_context_length) {
+    short_buffer = real_mac_length > *mac_key_context_length;
+    *mac_key_context_length = real_mac_length;
+  }
+  if (enc_key_context_length) {
+    short_buffer = short_buffer || real_enc_length > *enc_key_context_length;
+    *enc_key_context_length = real_enc_length;
+  }
+  if (short_buffer || !mac_key_context || !enc_key_context) {
+    return OEMCrypto_ERROR_SHORT_BUFFER;
+  }
+
+  if (!context || !mac_key_context_length || !enc_key_context_length) {
+    return OEMCrypto_ERROR_INVALID_CONTEXT;
+  }
+
+  memcpy(mac_key_context, ODK_MacKeyLabelWithZero,
+         ODK_MacKeyLabelWithZeroLength);
+  memcpy(mac_key_context + ODK_MacKeyLabelWithZeroLength, context,
+         context_length);
+  memcpy(mac_key_context + ODK_MacKeyLabelWithZeroLength + context_length,
+         ODK_MacKeySuffix, ODK_MacKeySuffixLength);
+
+  memcpy(enc_key_context, ODK_EncKeyLabelWithZero,
+         ODK_EncKeyLabelWithZeroLength);
+  memcpy(enc_key_context + ODK_EncKeyLabelWithZeroLength, context,
+         context_length);
+  memcpy(enc_key_context + ODK_EncKeyLabelWithZeroLength + context_length,
+         ODK_EncKeySuffix, ODK_EncKeySuffixLength);
+
+  return OEMCrypto_SUCCESS;
+}