How to set password to zip file with libZip

Question

I'm using libZip in my project, I success to create zip file output, but I'm having difficulty to set a password to a zip file.

I'm calling the zip_set_default_password fucntion and I'm getting the OK response, but when I'm trying to extract it didn't ask for a password.

Code sample:

int CompressWithPassword(const char * psFileContent, int iFileSize, const char * pcPassword)
{
    zip_source *psZipSource = NULL;
    zip_int64_t iIndex = 0;
    int iError = EOK;
    const char * pcZipOutputPath = "/home/user/Documents/myzip.zip";

    // Open zip file.
    m_psZip =
            zip_open(pcZipOutputPath,
                    ZIP_CREATE /*Create the archive if it does not exist*/,
                    &iError);

    // Zip opend ?
    if(iError != ZIP_ER_OK)
    {
        Close();
        return iError;
    }

    // Generate zip source content.
    psZipSource =
            zip_source_buffer(m_psZip,
                              psFileContent,
                              iFileSize,
                              0);

    // Valid zip source ?
    if(psZipSource == NULL)
    {
        Close();
        iError = -1;
        return iError;
    }

    iIndex =
            zip_file_add(m_psZip,
                         pcZipOutputPath,
                         psZipSource, ZIP_FL_OVERWRITE);
    if(iIndex < 0)
    {    
        Close();
        return iIndex;
    }

    // Create password
    int iRetPassword =
                zip_set_default_password(m_psZip, pcPassword);

    // password set ?
    if (iRetPassword == -1)
    {
        Close();
        return iRetPassword;
    }

    // Close zip file.
    Close();

    return iError;
}

When I'm calling this function, I'm getting OK and the zip file is created, What I'm missing here?

LibZip version 1.1.3-1, OS: fedora 25

Thanks.

Not related to what you are asking, but; you do know that the password on a zip file is trivially breakable - right? Don't rely on that for any real security. — Jesper Juhl, Feb 04 '18 at 16:11
From the function name and documentation it seems that `zip_set_default_password` only sets the default password for when encryption is used it says nothing about activating encryption. You probably also need to call https://libzip.org/documentation/zip_file_set_encryption.html — Eelke, Feb 04 '18 at 16:22
@Eelke, thanks for your clarification, I now see that `zip_file_set_encryption` is from libzip version 1.2, and I'm using the older version 1.1.3, so I'll have to update first, and then I'll test it, thanks! — Simon, Feb 04 '18 at 16:36

score 2 · Answer 1 · answered Feb 07 '22 at 19:13

I saw that has a lot of people searching by this question, then i'll make an example of zip_file_set_encryption, the method basically ask for zip archive, file index,encryption method and the password:

int main(){
    int errCode = 0;
    zip *z = zip_open("package.zip",ZIP_CREATE,&errCode);

    zip_source_t *source;

    char buffer[] = "Hello world!";
    source = zip_source_buffer(z,buffer,strlen(buffer),0);
    zip_file_add(z,"example.txt",source,0);

    /* Available encryption methods: 
    ZIP_EM_AES_128
    ZIP_EM_AES_192
    ZIP_EM_AES_256
    */

    zip_file_set_encryption(z,/* Index of the file */ 0,/* Encryption method */ ZIP_EM_AES_256,/* Password to encrypt file */ "myPassword");

    zip_close(z);
};

then when i use 7-zip to open the zip file created by my program:

7z e package.zip

It just prompt the password to me, if you type the correct then the files in your workspace will be filled with the content:

Enter password (will not be echoed):

with the libzip is possible set file password by name, but with a little process before:

int main(){
    int errCode = 0;
    zip *z = zip_open("package.zip",ZIP_CREATE,&errCode);

    zip_source_t *source;

    char buffer[] = "Hello world!";
    source = zip_source_buffer(z,buffer,strlen(buffer),0);
    zip_file_add(z,"example.txt",source,0);

    source = zip_source_buffer(z,buffer,strlen(buffer),0);
    zip_file_add(z,"example2.txt",source,0);

    // Create struct of file stat
    struct zip_stat st;

    // Fill the struct with the file name that you want
    zip_stat(z,"example2.txt",0,&st);

    // Set the password to the file using index that had got by name

    /* Available encryption methods: 
    ZIP_EM_AES_128
    ZIP_EM_AES_192
    ZIP_EM_AES_256
    */

    zip_file_set_encryption(z,/* Index of file */ st.index, /* encryption method */ ZIP_EM_AES_256, /* password */"myPassword");

    zip_close(z);
};

I'm creating an wrapper for libzip (not complete yet), an easy way to interact with zip files, the GitHub URL is there: https://github.com/Romulo-Moraes/zipCrafter

Caution, if you set an password to a file, you should set the same password for the whole zip file, cause it can generate an error when you try open with 7-zip, it will try open the first file with your password then will try the same password for the whole zip.

Some unzip program versions will skip your file that was set with password by libzip, i recommend 7-zip

`zip_file_add` returns the index of just added file, so you do not need to call `zip_stat` for that — Fedor, Feb 07 '22 at 20:39
Yes, thanks for comment, i just wanted show a way for do it by file name, sometimes is more human readable than just numbers. — Rômulo peres de moraes, Feb 08 '22 at 04:53

score 1 · Answer 2 · answered Mar 04 '19 at 08:54

1

As written in the Libzip Documentation here, 'zip_set_default_password' will "sets the default password used when accessing encrypted files", if you use 'zip_fopen' to open files. otherwise, if you have a different password for single files you can use 'zip_fopen_encrypted' to open them.

If you want to encrypt files you add to an archive you need to use 'zip_file_set_encryption' with (m_psZip, iIndex, method you choose, pcPassword).

answered Mar 04 '19 at 08:54

Tomer L

21
3

Some example how to use `zip_file_set_encryption` would be great, because it is not easy to find such in the web. – Fedor Feb 04 '22 at 17:35

How to set password to zip file with libZip

2 Answers2