Skip to content

Instantly share code, notes, and snippets.

@roobre

roobre/aesctr.go

Created Apr 14, 2018
Embed
What would you like to do?
Encrypt/Decrypt a file with AES-CTR
package main
import (
"bufio"
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"encoding/hex"
"fmt"
"github.com/urfave/cli"
"io/ioutil"
"log"
"os"
)
const BLOCKSIZE_BYTE = 16
const BLOCKSIZE_BIT = 16 * 8
func main() {
app := cli.NewApp()
app.Name = "pscrypt"
app.Usage = "pscrypt "
app.Description = "Encrypt video files in AES CTR provided a key and optionally and IV"
app.Version = "0.1.0"
app.Action = pscrypt
app.Flags = []cli.Flag{
cli.StringFlag{
Name: "in, i",
Usage: "Input file",
},
cli.StringFlag{
Name: "out, o",
Usage: "Output file",
},
cli.StringFlag{
Name: "key, k",
Usage: fmt.Sprintf("Key as %d-byte hex string (%d characters)", BLOCKSIZE_BYTE, hex.EncodedLen(BLOCKSIZE_BYTE)),
},
cli.BoolFlag{
Name: "implicit-encrypt, E",
Usage: fmt.Sprintf("Generate a random %d-byte IV and prepend it to the output file", BLOCKSIZE_BYTE),
},
cli.BoolFlag{
Name: "implicit-decrypt, D",
Usage: fmt.Sprintf("Use first %d bytes of file as IV for decryption", BLOCKSIZE_BYTE),
},
cli.StringFlag{
Name: "iv",
Usage: fmt.Sprintf("IV as %d-byte hex string (%d characters)", BLOCKSIZE_BYTE, hex.EncodedLen(BLOCKSIZE_BYTE)),
Value: "",
},
}
app.Run(os.Args)
}
func pscrypt(ctx *cli.Context) error {
if ctx.String("in") == "" ||
ctx.String("out") == "" ||
ctx.String("key") == "" ||
ctx.Bool("implicit-decrypt") && ctx.Bool("implicit-encrypt") ||
(ctx.String("iv") == "" && !(ctx.Bool("implicit-decrypt") || ctx.Bool("implicit-encrypt"))) {
cli.ShowAppHelp(ctx)
return nil
}
in, err := os.Open(ctx.String("in"))
check(err)
ir := bufio.NewReader(in)
out, err := os.Create(ctx.String("out"))
check(err)
ow := bufio.NewWriter(out)
key := make([]byte, BLOCKSIZE_BYTE)
n, err := hex.Decode(key, []byte(ctx.String("key")))
check(err)
if n != BLOCKSIZE_BYTE {
log.Fatalf("Provided key is not %d b long", BLOCKSIZE_BIT)
}
iv := make([]byte, BLOCKSIZE_BYTE)
source, err := ioutil.ReadAll(ir)
if ctx.String("iv") != "" {
n, err = hex.Decode(key, []byte(ctx.String("iv")))
check(err)
if n != BLOCKSIZE_BYTE {
log.Fatalf("Provided IV is not %d b long", BLOCKSIZE_BIT)
}
} else {
if ctx.Bool("implicit-decrypt") {
copy(iv, source[:BLOCKSIZE_BYTE])
source = source[BLOCKSIZE_BYTE:]
} else if ctx.Bool("implicit-encrypt") {
n, err = rand.Read(iv)
check(err)
if n != BLOCKSIZE_BYTE {
log.Fatalf("Error gathering %d random bytes for IV", BLOCKSIZE_BIT)
}
ow.Write(iv)
} else {
log.Fatal("You need to provide an IV or use -I/-E option.")
}
}
aesCipher, err := aes.NewCipher(key)
check(err)
ctr := cipher.NewCTR(aesCipher, iv)
destination := make([]byte, len(source))
check(err)
ctr.XORKeyStream(destination, source)
ow.Write(destination)
return nil
}
func check(err error) {
if err != nil {
log.Fatal(err)
}
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
You can’t perform that action at this time.