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cipher.go
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cipher.go
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package main
import (
"bytes"
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"encoding/base64"
"errors"
"io"
)
func pad(src []byte) []byte {
padding := aes.BlockSize - len(src)%aes.BlockSize
padtext := bytes.Repeat([]byte{byte(padding)}, padding)
return append(src, padtext...)
}
func unpad(src []byte) ([]byte, error) {
length := len(src)
unpadding := int(src[length-1])
if unpadding > length {
return nil, errors.New("unpad error. This could happen when incorrect encryption key is used")
}
return src[:(length - unpadding)], nil
}
func encrypt(key []byte, text string) (string, error) {
block, err := aes.NewCipher(key)
if err != nil {
return "", err
}
msg := pad([]byte(text))
ciphertext := make([]byte, aes.BlockSize+len(msg))
iv := ciphertext[:aes.BlockSize]
if _, err := io.ReadFull(rand.Reader, iv); err != nil {
return "", err
}
cfb := cipher.NewCFBEncrypter(block, iv)
cfb.XORKeyStream(ciphertext[aes.BlockSize:], msg)
finalMsg := base64.URLEncoding.EncodeToString(ciphertext)
return finalMsg, nil
}
func decrypt(key []byte, text string) (string, error) {
block, err := aes.NewCipher(key)
if err != nil {
return "", err
}
decodedMsg, err := base64.URLEncoding.DecodeString(text)
if err != nil {
return "", err
}
if (len(decodedMsg) % aes.BlockSize) != 0 {
return "", errors.New("blocksize must be multiple of decoded message length")
}
iv := decodedMsg[:aes.BlockSize]
msg := decodedMsg[aes.BlockSize:]
cfb := cipher.NewCFBDecrypter(block, iv)
cfb.XORKeyStream(msg, msg)
unpadMsg, err := unpad(msg)
if err != nil {
return "", err
}
return string(unpadMsg), nil
}