1 files changed, 269 insertions, 0 deletions
diff --git a/drm/mediadrm/plugins/clearkey/JsonWebKey.cpp b/drm/mediadrm/plugins/clearkey/JsonWebKey.cpp
new file mode 100644
index 0000000..53ffae4
--- /dev/null
+++ b/drm/mediadrm/plugins/clearkey/JsonWebKey.cpp
@@ -0,0 +1,269 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#define LOG_TAG "JsonWebKey"
+
+#include <media/stagefright/foundation/ABuffer.h>
+#include <media/stagefright/foundation/AString.h>
+#include <media/stagefright/foundation/base64.h>
+#include <utils/Log.h>
+
+#include "JsonWebKey.h"
+
+namespace {
+const android::String8 kKeysTag("keys");
+const android::String8 kKeyTypeTag("kty");
+const android::String8 kSymmetricKeyValue("oct");
+const android::String8 kKeyTag("k");
+const android::String8 kKeyIdTag("kid");
+const android::String8 kBase64Padding("=");
+}
+
+namespace clearkeydrm {
+
+using android::ABuffer;
+using android::AString;
+
+JsonWebKey::JsonWebKey() {
+}
+
+JsonWebKey::~JsonWebKey() {
+}
+
+/*
+ * Parses a JSON Web Key Set string, initializes a KeyMap with key id:key
+ * pairs from the JSON Web Key Set. Both key ids and keys are base64url
+ * encoded. The KeyMap contains base64url decoded key id:key pairs.
+ *
+ * @return Returns false for errors, true for success.
+ */
+bool JsonWebKey::extractKeysFromJsonWebKeySet(const String8& jsonWebKeySet,
+        KeyMap* keys) {
+
+    keys->clear();
+    if (!parseJsonWebKeySet(jsonWebKeySet, &mJsonObjects)) {
+        return false;
+    }
+
+    // mJsonObjects[0] contains the entire JSON Web Key Set, including
+    // all the base64 encoded keys. Each key is also stored separately as
+    // a JSON object in mJsonObjects[1..n] where n is the total
+    // number of keys in the set.
+    if (!isJsonWebKeySet(mJsonObjects[0])) {
+        return false;
+    }
+
+    String8 encodedKey, encodedKeyId;
+    Vector<uint8_t> decodedKey, decodedKeyId;
+
+    // mJsonObjects[1] contains the first JSON Web Key in the set
+    for (size_t i = 1; i < mJsonObjects.size(); ++i) {
+        encodedKeyId.clear();
+        encodedKey.clear();
+
+        if (!parseJsonObject(mJsonObjects[i], &mTokens))
+            return false;
+
+        if (findKey(mJsonObjects[i], &encodedKeyId, &encodedKey)) {
+            if (encodedKeyId.isEmpty() || encodedKey.isEmpty()) {
+                ALOGE("Must have both key id and key in the JsonWebKey set.");
+                continue;
+            }
+
+            if (!decodeBase64String(encodedKeyId, &decodedKeyId)) {
+                ALOGE("Failed to decode key id(%s)", encodedKeyId.string());
+                continue;
+            }
+
+            if (!decodeBase64String(encodedKey, &decodedKey)) {
+                ALOGE("Failed to decode key(%s)", encodedKey.string());
+                continue;
+            }
+
+            keys->add(decodedKeyId, decodedKey);
+        }
+    }
+    return true;
+}
+
+bool JsonWebKey::decodeBase64String(const String8& encodedText,
+        Vector<uint8_t>* decodedText) {
+
+    decodedText->clear();
+
+    // encodedText should not contain padding characters as per EME spec.
+    if (encodedText.find(kBase64Padding) != -1) {
+        return false;
+    }
+
+    // Since android::decodeBase64() requires padding characters,
+    // add them so length of encodedText is exactly a multiple of 4.
+    int remainder = encodedText.length() % 4;
+    String8 paddedText(encodedText);
+    if (remainder > 0) {
+        for (int i = 0; i < 4 - remainder; ++i) {
+            paddedText.append(kBase64Padding);
+        }
+    }
+
+    android::sp<ABuffer> buffer =
+            android::decodeBase64(AString(paddedText.string()));
+    if (buffer == NULL) {
+        ALOGE("Malformed base64 encoded content found.");
+        return false;
+    }
+
+    decodedText->appendArray(buffer->base(), buffer->size());
+    return true;
+}
+
+bool JsonWebKey::findKey(const String8& jsonObject, String8* keyId,
+        String8* encodedKey) {
+
+    String8 key, value;
+
+    // Only allow symmetric key, i.e. "kty":"oct" pair.
+    if (jsonObject.find(kKeyTypeTag) >= 0) {
+        findValue(kKeyTypeTag, &value);
+        if (0 != value.compare(kSymmetricKeyValue))
+            return false;
+    }
+
+    if (jsonObject.find(kKeyIdTag) >= 0) {
+        findValue(kKeyIdTag, keyId);
+    }
+
+    if (jsonObject.find(kKeyTag) >= 0) {
+        findValue(kKeyTag, encodedKey);
+    }
+    return true;
+}
+
+void JsonWebKey::findValue(const String8 &key, String8* value) {
+    value->clear();
+    const char* valueToken;
+    for (Vector<String8>::const_iterator nextToken = mTokens.begin();
+        nextToken != mTokens.end(); ++nextToken) {
+        if (0 == (*nextToken).compare(key)) {
+            if (nextToken + 1 == mTokens.end())
+                break;
+            valueToken = (*(nextToken + 1)).string();
+            value->setTo(valueToken);
+            nextToken++;
+            break;
+        }
+    }
+}
+
+bool JsonWebKey::isJsonWebKeySet(const String8& jsonObject) const {
+    if (jsonObject.find(kKeysTag) == -1) {
+        ALOGE("JSON Web Key does not contain keys.");
+        return false;
+    }
+    return true;
+}
+
+/*
+ * Parses a JSON objects string and initializes a vector of tokens.
+ *
+ * @return Returns false for errors, true for success.
+ */
+bool JsonWebKey::parseJsonObject(const String8& jsonObject,
+        Vector<String8>* tokens) {
+    jsmn_parser parser;
+
+    jsmn_init(&parser);
+    int numTokens = jsmn_parse(&parser,
+        jsonObject.string(), jsonObject.size(), NULL, 0);
+    if (numTokens < 0) {
+        ALOGE("Parser returns error code=%d", numTokens);
+        return false;
+    }
+
+    unsigned int jsmnTokensSize = numTokens * sizeof(jsmntok_t);
+    mJsmnTokens.clear();
+    mJsmnTokens.setCapacity(jsmnTokensSize);
+
+    jsmn_init(&parser);
+    int status = jsmn_parse(&parser, jsonObject.string(),
+        jsonObject.size(), mJsmnTokens.editArray(), numTokens);
+    if (status < 0) {
+        ALOGE("Parser returns error code=%d", status);
+        return false;
+    }
+
+    tokens->clear();
+    String8 token;
+    const char *pjs;
+    for (int j = 0; j < numTokens; ++j) {
+        pjs = jsonObject.string() + mJsmnTokens[j].start;
+        if (mJsmnTokens[j].type == JSMN_STRING ||
+                mJsmnTokens[j].type == JSMN_PRIMITIVE) {
+            token.setTo(pjs, mJsmnTokens[j].end - mJsmnTokens[j].start);
+            tokens->add(token);
+        }
+    }
+    return true;
+}
+
+/*
+ * Parses JSON Web Key Set string and initializes a vector of JSON objects.
+ *
+ * @return Returns false for errors, true for success.
+ */
+bool JsonWebKey::parseJsonWebKeySet(const String8& jsonWebKeySet,
+        Vector<String8>* jsonObjects) {
+    if (jsonWebKeySet.isEmpty()) {
+        ALOGE("Empty JSON Web Key");
+        return false;
+    }
+
+    // The jsmn parser only supports unicode encoding.
+    jsmn_parser parser;
+
+    // Computes number of tokens. A token marks the type, offset in
+    // the original string.
+    jsmn_init(&parser);
+    int numTokens = jsmn_parse(&parser,
+            jsonWebKeySet.string(), jsonWebKeySet.size(), NULL, 0);
+    if (numTokens < 0) {
+        ALOGE("Parser returns error code=%d", numTokens);
+        return false;
+    }
+
+    unsigned int jsmnTokensSize = numTokens * sizeof(jsmntok_t);
+    mJsmnTokens.setCapacity(jsmnTokensSize);
+
+    jsmn_init(&parser);
+    int status = jsmn_parse(&parser, jsonWebKeySet.string(),
+            jsonWebKeySet.size(), mJsmnTokens.editArray(), numTokens);
+    if (status < 0) {
+        ALOGE("Parser returns error code=%d", status);
+        return false;
+    }
+
+    String8 token;
+    const char *pjs;
+    for (int i = 0; i < numTokens; ++i) {
+        pjs = jsonWebKeySet.string() + mJsmnTokens[i].start;
+        if (mJsmnTokens[i].type == JSMN_OBJECT) {
+            token.setTo(pjs, mJsmnTokens[i].end - mJsmnTokens[i].start);
+            jsonObjects->add(token);
+        }
+    }
+    return true;
+}
+
+}  // clearkeydrm