Golang 1.2: Unzip password protected zip file?

Question

Looking at the latest release (1.2) zip package - how can I unzip a file that was password protected (using 7zip, AES-256 encoding)? I don't see where/how to add in that information. A simple example would be great!

Answer 1

The archive/zip package seems to only provide basic zip functionality. I would use 7zip to unzip password protected zip files using the os/exec package.

Online 7-zip user guide

The best guide for understanding 7zip is 7-zip.chm, which is in the zip file for the windows command line.

The following code isn't optimal but it shows you how to get the job done.

Code for extracting a password protected zip using 7zip

func extractZipWithPassword() {
    fmt.Printf("Unzipping `%s` to directory `%s`\n", zip_path, extract_path)
    commandString := fmt.Sprintf(`7za e %s -o%s -p"%s" -aoa`, zip_path, extract_path, zip_password)
    commandSlice := strings.Fields(commandString)
    fmt.Println(commandString)
    c := exec.Command(commandSlice[0], commandSlice[1:]...)
    e := c.Run()
    checkError(e)
}

Example Program

// Shows how to extract an passsword encrypted zip file using 7zip.
// By Larry Battle <https://github.com/LarryBattle>
// Answer to http://stackoverflow.com/questions/20330210/golang-1-2-unzip-password-protected-zip-file
// 7-zip.chm - http://sevenzip.sourceforge.jp/chm/cmdline/switches/index.htm
// Effective Golang - http://golang.org/doc/effective_go.html
package main

import (
    "fmt"
    "os"
    "os/exec"
    "path/filepath"
    "strings"
)

var (
    txt_content     = "Sample file created."
    txt_filename    = "name.txt"
    zip_filename    = "sample.zip"
    zip_password    = "42"
    zip_encryptType = "AES256"
    base_path       = "./"

    test_path          = filepath.Join(base_path, "test")
    src_path           = filepath.Join(test_path, "src")
    extract_path       = filepath.Join(test_path, "extracted")
    extracted_txt_path = filepath.Join(extract_path, txt_filename)
    txt_path           = filepath.Join(src_path, txt_filename)
    zip_path           = filepath.Join(src_path, zip_filename)
)
var txt_fileSize int64

func checkError(e error) {
    if e != nil {
        panic(e)
    }
}
func setupTestDir() {
    fmt.Printf("Removing `%s`\n", test_path)
    var e error
    os.Remove(test_path)
    fmt.Printf("Creating `%s`,`%s`\n", extract_path, src_path)
    e = os.MkdirAll(src_path, os.ModeDir|os.ModePerm)
    checkError(e)
    e = os.MkdirAll(extract_path, os.ModeDir|os.ModePerm)
    checkError(e)
}
func createSampleFile() {
    fmt.Println("Creating", txt_path)
    file, e := os.Create(txt_path)
    checkError(e)
    defer file.Close()
    _, e = file.WriteString(txt_content)
    checkError(e)
    fi, e := file.Stat()
    txt_fileSize = fi.Size()
}
func createZipWithPassword() {
    fmt.Println("Creating", zip_path)
    commandString := fmt.Sprintf(`7za a %s %s -p"%s" -mem=%s`, zip_path, txt_path, zip_password, zip_encryptType)
    commandSlice := strings.Fields(commandString)
    fmt.Println(commandString)
    c := exec.Command(commandSlice[0], commandSlice[1:]...)
    e := c.Run()
    checkError(e)
}
func extractZipWithPassword() {
    fmt.Printf("Unzipping `%s` to directory `%s`\n", zip_path, extract_path)
    commandString := fmt.Sprintf(`7za e %s -o%s -p"%s" -aoa`, zip_path, extract_path, zip_password)
    commandSlice := strings.Fields(commandString)
    fmt.Println(commandString)
    c := exec.Command(commandSlice[0], commandSlice[1:]...)
    e := c.Run()
    checkError(e)
}
func checkFor7Zip() {
    _, e := exec.LookPath("7za")
    if e != nil {
        fmt.Println("Make sure 7zip is install and include your path.")
    }
    checkError(e)
}
func checkExtractedFile() {
    fmt.Println("Reading", extracted_txt_path)
    file, e := os.Open(extracted_txt_path)
    checkError(e)
    defer file.Close()
    buf := make([]byte, txt_fileSize)
    n, e := file.Read(buf)
    checkError(e)
    if !strings.Contains(string(buf[:n]), strings.Fields(txt_content)[0]) {
        panic(fmt.Sprintf("File`%s` is corrupted.\n", extracted_txt_path))
    }
}
func main() {
    fmt.Println("# Setup")
    checkFor7Zip()
    setupTestDir()
    createSampleFile()
    createZipWithPassword()
    fmt.Println("# Answer to question...")
    extractZipWithPassword()
    checkExtractedFile()
    fmt.Println("Done.")
}

Output

# Setup
Removing `test`
Creating `test/extracted`,`test/src`
Creating test/src/name.txt
Creating test/src/sample.zip
7za a test/src/sample.zip test/src/name.txt -p"42" -mem=AES256
# Answer to question...
Unzipping `test/src/sample.zip` to directory `test/extracted`
7za e test/src/sample.zip -otest/extracted -p"42" -aoa
Reading test/extracted/name.txt
Done.

Answer 2

If anyone else runs into this the extraction failing with a password error, try removing the quotes. In my case they were being escaped by go and was causing the extraction to fail.

Answer 3

https://github.com/yeka/zip provides functionality to extract password protected zip file (AES & Zip Standard Encryption aka ZipCrypto).

Below is an example how to use it:

package main

import (
    "os"
    "io"
    "github.com/yeka/zip"
)

func main() {
    file := "file.zip"
    password := "password"
    r, err := zip.OpenReader(file)
    if nil != err {
        panic(err)
    }
    defer r.Close()

    for _, f := range r.File {
        f.SetPassword(password)
        w, err := os.Create(f.Name)
        if nil != err {
            panic(err)
        }
        io.Copy(w, f)
        w.Close()
    }
}

The work is a fork from https://github.com/alexmullins/zip which add support for AES only.