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gcm.go
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gcm.go
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package aes
import (
"bytes"
"crypto/aes"
"crypto/cipher"
"encoding/hex"
"errors"
"flag"
"fmt"
"io"
"os"
)
func Gcm(args []string) error {
fset := flag.NewFlagSet("aes-gcm", flag.ContinueOnError)
fset.Usage = func() {
fmt.Fprint(os.Stderr, `Usage: pocryp aes-gcm [-e/-d] -key|-key-file -iv -aad [-in INPUT] [-out OUTPUT]
Encrypt/Decrypt INPUT to OUTPUT using AES-GCM.
If -in is not specified, stdin will be read.
If -out is not specified, the output will be printed to stdout.
Options:
`)
fset.PrintDefaults()
}
fEncrypt := fset.Bool("e", false, "Encrypt the input to the output. Default if omitted.")
fDecrypt := fset.Bool("d", false, "Decrypt the input to the output.")
fOutput := fset.String("out", "", "Write the result to the file at path OUTPUT.")
fInput := fset.String("in", "", "Read data from the file at path INPUT.")
fKey := fset.String("key", "", "Key as hex.")
fKeyFile := fset.String("key-file", "", "File which contains the key as binary/text.")
fIV := fset.String("iv", "", "IV as hex.")
fAAD := fset.String("aad", "", "File which contains additional associated data as binary/text.")
if err := fset.Parse(args); err != nil {
return err
}
if *fKey == "" && *fKeyFile == "" {
fset.Usage()
return errors.New("no key specified, use -key or -key-file to specify it")
}
if *fKey != "" && *fKeyFile != "" {
fset.Usage()
return errors.New("cannot use -key and -key-file at the same time")
}
if *fIV == "" {
fset.Usage()
return errors.New("no IV specified, use -iv to specify it")
}
var key []byte
if *fKey != "" {
b, err := hex.DecodeString(*fKey)
if err != nil {
return err
}
key = b
}
if *fKeyFile != "" {
b, err := os.ReadFile(*fKeyFile)
if err != nil {
return err
}
key = b
}
iv, err := hex.DecodeString(*fIV)
if err != nil {
return err
}
var aad []byte
if *fAAD != "" {
b, err := os.ReadFile(*fAAD)
if err != nil {
return err
}
aad = b
}
var r io.Reader
if *fInput == "" {
r = os.Stdin
} else {
f, err := os.Open(*fInput)
if err != nil {
return err
}
defer f.Close()
r = f
}
var w io.Writer
if *fOutput == "" {
w = os.Stdout
} else {
f, err := os.Create(*fOutput)
if err != nil {
return err
}
defer f.Close()
w = f
}
var input bytes.Buffer
if _, err := io.Copy(&input, r); err != nil {
return err
}
var output []byte
switch {
case *fEncrypt:
output, err = gcm(key, iv, input.Bytes(), aad, true)
case *fDecrypt:
output, err = gcm(key, iv, input.Bytes(), aad, false)
default:
output, err = gcm(key, iv, input.Bytes(), aad, true)
}
if err != nil {
return err
}
if _, err := io.Copy(w, bytes.NewBuffer(output)); err != nil {
return err
}
return nil
}
func gcm(key, nonce, in, additionalData []byte, direction bool) ([]byte, error) {
block, err := aes.NewCipher(key)
if err != nil {
return nil, err
}
c, err := cipher.NewGCMWithNonceSize(block, len(nonce))
if err != nil {
return nil, err
}
if direction {
return c.Seal(nil, nonce, in, additionalData), nil
}
return c.Open(nil, nonce, in, additionalData)
}