Android NDK get md5 of the binary file

Issue

DESCRIPTION

I'm trying to get md5 hash of the binary (.dex) file, which is stored in the /data/data/my.package.name/file.dex. I use Android NDK (C++).

PROBLEM

Several ways to get hash of the file:

1. From my laptop: md5sum file.dex -> 5a65273b2ee336ad2c45a9306be162f6
2. Using adb shell:md5sum file.dex -> 5a65273b2ee336ad2c45a9306be162f6
3. From my C++ code:

    int err = 0;
    zip *z = zip_open(getBaseApkAbsolutePath(), 0, &err);

    const char *name = "classes.dex";
    struct zip_stat st;
    zip_stat_init(&st);
    zip_stat(z, name, 0, &st);

    char *contents = new char[st.size];

    zip_file *f = zip_fopen(z, name, 0);
    zip_fread(f, contents, st.size);

    std::ofstream ofstream;
    ofstream.open("/data/data/my.package/classes.dex", std::ofstream::binary);
    ofstream.write(contents, st.size);

    joyee::MD5 md5 = joyee::MD5();
    md5.update(contents, sizeof(contents));
    md5.finalize();

    LOG(md5.toString());
    LOG(joyee::md5(contents));

    zip_fclose(f);
    zip_close(z);

And then I get this -> aaaeb407992f9fe57cc6235ece90ec35

CLARIFICATION

1. My code works well with simple string like Hello, World!
2. MD5 implementation works well

QUESTION

How can I get md5 hash of the binary file in Android using C++ ?

Solution

Here is the problem:

md5.update(contents, sizeof(contents));

You're taking the size of your pointer (which is 4 or 8) instead of the buffer it points to. So effectively you are calculating the md5sum of those first few bytes. Pass st.size instead to check the full file.

Answered By - Botje