OBB: use PBKDF2 for key generation.

Switch to using PBKDF2 for the key generation for OBBs. Any previously
generated OBBs will stop being read correctly. A small pbkdf2gen program
is available to allow generation of appropriate keys with the salts.

Bug: 3059950
Change-Id: If4305c989fd692fd1150eb270dbf751e09c37295

include/utils/ObbFile.h

@@ -27,6 +27,7 @@ namespace android {
 
 // OBB flags (bit 0)
 #define OBB_OVERLAY         (1 << 0)
+#define OBB_SALTED          (1 << 1)
 
 class ObbFile : public RefBase {
 protected:
@@ -70,6 +71,26 @@ public:
         mFlags = flags;
     }
 
+    const unsigned char* getSalt(size_t* length) const {
+        if ((mFlags & OBB_SALTED) == 0) {
+            *length = 0;
+            return NULL;
+        }
+
+        *length = sizeof(mSalt);
+        return mSalt;
+    }
+
+    bool setSalt(const unsigned char* salt, size_t length) {
+        if (length != sizeof(mSalt)) {
+            return false;
+        }
+
+        memcpy(mSalt, salt, sizeof(mSalt));
+        mFlags |= OBB_SALTED;
+        return true;
+    }
+
     bool isOverlay() {
         return (mFlags & OBB_OVERLAY) == OBB_OVERLAY;
     }
@@ -103,6 +124,12 @@ private:
     /* Flags for this OBB type. */
     int32_t mFlags;
 
+    /* Whether the file is salted. */
+    bool mSalted;
+
+    /* The encryption salt. */
+    unsigned char mSalt[8];
+
     const char* mFileName;
 
     size_t mFileSize;

libs/utils/ObbFile.cpp

@@ -29,10 +29,11 @@
 
 #define kFooterTagSize 8  /* last two 32-bit integers */
 
-#define kFooterMinSize 25 /* 32-bit signature version (4 bytes)
+#define kFooterMinSize 33 /* 32-bit signature version (4 bytes)
                            * 32-bit package version (4 bytes)
                            * 32-bit flags (4 bytes)
-                           * 32-bit package name size (4-bytes)
+                           * 64-bit salt (8 bytes)
+                           * 32-bit package name size (4 bytes)
                            * >=1-character package name (1 byte)
                            * 32-bit footer size (4 bytes)
                            * 32-bit footer marker (4 bytes)
@@ -47,8 +48,9 @@
 /* offsets in version 1 of the header */
 #define kPackageVersionOffset 4
 #define kFlagsOffset          8
-#define kPackageNameLenOffset 12
+#define kSaltOffset           12
-#define kPackageNameOffset    16
+#define kPackageNameLenOffset 20
+#define kPackageNameOffset    24
 
 /*
  * TEMP_FAILURE_RETRY is defined by some, but not all, versions of
@@ -79,11 +81,12 @@ typedef off64_t my_off64_t;
 
 namespace android {
 
-ObbFile::ObbFile() :
+ObbFile::ObbFile()
-        mPackageName(""),
+        : mPackageName("")
-        mVersion(-1),
+        , mVersion(-1)
-        mFlags(0)
+        , mFlags(0)
 {
+    memset(mSalt, 0, sizeof(mSalt));
 }
 
 ObbFile::~ObbFile() {
@@ -192,7 +195,7 @@ bool ObbFile::parseObbFile(int fd)
 
 #ifdef DEBUG
     for (int i = 0; i < footerSize; ++i) {
-        LOGI("char: 0x%02x", scanBuf[i]);
+        LOGI("char: 0x%02x\n", scanBuf[i]);
     }
 #endif
 
@@ -206,6 +209,8 @@ bool ObbFile::parseObbFile(int fd)
     mVersion = (int32_t) get4LE((unsigned char*)scanBuf + kPackageVersionOffset);
     mFlags = (int32_t) get4LE((unsigned char*)scanBuf + kFlagsOffset);
 
+    memcpy(&mSalt, (unsigned char*)scanBuf + kSaltOffset, sizeof(mSalt));
+
     uint32_t packageNameLen = get4LE((unsigned char*)scanBuf + kPackageNameLenOffset);
     if (packageNameLen <= 0
             || packageNameLen > (footerSize - kPackageNameOffset)) {
@@ -255,7 +260,7 @@ bool ObbFile::writeTo(int fd)
     my_lseek64(fd, 0, SEEK_END);
 
     if (mPackageName.size() == 0 || mVersion == -1) {
-        LOGW("tried to write uninitialized ObbFile data");
+        LOGW("tried to write uninitialized ObbFile data\n");
         return false;
     }
 
@@ -264,43 +269,48 @@ bool ObbFile::writeTo(int fd)
 
     put4LE(intBuf, kSigVersion);
     if (write(fd, &intBuf, sizeof(uint32_t)) != (ssize_t)sizeof(uint32_t)) {
-        LOGW("couldn't write signature version: %s", strerror(errno));
+        LOGW("couldn't write signature version: %s\n", strerror(errno));
         return false;
     }
 
     put4LE(intBuf, mVersion);
     if (write(fd, &intBuf, sizeof(uint32_t)) != (ssize_t)sizeof(uint32_t)) {
-        LOGW("couldn't write package version");
+        LOGW("couldn't write package version\n");
         return false;
     }
 
     put4LE(intBuf, mFlags);
     if (write(fd, &intBuf, sizeof(uint32_t)) != (ssize_t)sizeof(uint32_t)) {
-        LOGW("couldn't write package version");
+        LOGW("couldn't write package version\n");
+        return false;
+    }
+
+    if (write(fd, mSalt, sizeof(mSalt)) != (ssize_t)sizeof(mSalt)) {
+        LOGW("couldn't write salt: %s\n", strerror(errno));
         return false;
     }
 
     size_t packageNameLen = mPackageName.size();
     put4LE(intBuf, packageNameLen);
     if (write(fd, &intBuf, sizeof(uint32_t)) != (ssize_t)sizeof(uint32_t)) {
-        LOGW("couldn't write package name length: %s", strerror(errno));
+        LOGW("couldn't write package name length: %s\n", strerror(errno));
         return false;
     }
 
     if (write(fd, mPackageName.string(), packageNameLen) != (ssize_t)packageNameLen) {
-        LOGW("couldn't write package name: %s", strerror(errno));
+        LOGW("couldn't write package name: %s\n", strerror(errno));
         return false;
     }
 
     put4LE(intBuf, kPackageNameOffset + packageNameLen);
     if (write(fd, &intBuf, sizeof(uint32_t)) != (ssize_t)sizeof(uint32_t)) {
-        LOGW("couldn't write footer size: %s", strerror(errno));
+        LOGW("couldn't write footer size: %s\n", strerror(errno));
         return false;
     }
 
     put4LE(intBuf, kSignature);
     if (write(fd, &intBuf, sizeof(uint32_t)) != (ssize_t)sizeof(uint32_t)) {
-        LOGW("couldn't write footer magic signature: %s", strerror(errno));
+        LOGW("couldn't write footer magic signature: %s\n", strerror(errno));
         return false;
     }
 

libs/utils/tests/ObbFile_test.cpp

@@ -23,6 +23,7 @@
 #include <gtest/gtest.h>
 
 #include <fcntl.h>
+#include <string.h>
 
 namespace android {
 
@@ -63,6 +64,10 @@ TEST_F(ObbFileTest, WriteThenRead) {
 
     mObbFile->setPackageName(String8(packageName));
     mObbFile->setVersion(versionNum);
+#define SALT_SIZE 8
+    unsigned char salt[SALT_SIZE] = {0x01, 0x10, 0x55, 0xAA, 0xFF, 0x00, 0x5A, 0xA5};
+    EXPECT_TRUE(mObbFile->setSalt(salt, SALT_SIZE))
+            << "Salt should be successfully set";
 
     EXPECT_TRUE(mObbFile->writeTo(mFileName))
             << "couldn't write to fake .obb file";
@@ -77,6 +82,19 @@ TEST_F(ObbFileTest, WriteThenRead) {
     const char* currentPackageName = mObbFile->getPackageName().string();
     EXPECT_STREQ(packageName, currentPackageName)
             << "package name didn't come out the same as it went in";
+
+    size_t saltLen;
+    const unsigned char* newSalt = mObbFile->getSalt(&saltLen);
+
+    EXPECT_EQ(sizeof(salt), saltLen)
+            << "salt sizes were not the same";
+
+    for (int i = 0; i < sizeof(salt); i++) {
+        EXPECT_EQ(salt[i], newSalt[i])
+                << "salt character " << i << " should be equal";
+    }
+    EXPECT_TRUE(memcmp(newSalt, salt, sizeof(salt)) == 0)
+            << "salts should be the same";
 }
 
 }