receiving crypto/rsa: decryption error when decrypting a file

Question

This is my decrypt function but it keeps returning: "crypto/rsa: decryption error". any advice would be helpful! I split the encryption into sections because the key kept raising the "key too short error". I am new to the encryption work in golang.

func DecryptFile(file string, privateKey *rsa.PrivateKey)([]byte, error){
  var decryptedBytes []byte
  // read the file into bytes
  data, err := ioutil.ReadFile(file)
  if err != nil {
    return decryptedBytes,err
  }
  fmt.Println(len(data))
  var decryptedByte []byte
  ByteSlice := split(data,200)
  rng := rand.Reader
  for _,bytes := range ByteSlice{
    decryptedBytes,err = rsa.DecryptOAEP(
      sha256.New(),
      rng,
      privateKey,
      bytes,
      nil)
    if err != nil {
     return decryptedBytes,err
    }
    decryptedBytes = append(decryptedBytes,decryptedByte...)
  }

  return decryptedBytes,nil
}

Encryption function:

func EncryptFile(file string, PublicKey *rsa.PublicKey)([]byte, error){
  var encryptedBytes []byte

  // read the file into bytes
  data, err := ioutil.ReadFile(file)
  if err != nil {
    return encryptedBytes,err
  }
  fmt.Println(len(data))
  // Encrypts the file
  //fmt.Println(PublicKey.N.BitLen())
  //_,_ = strconv.Atoi((PublicKey.N).String())
  ByteSlice := split(data,200)
  var encryptedByte []byte
  rng := rand.Reader
  for _,bytes := range ByteSlice{
    encryptedByte, err = rsa.EncryptOAEP(
         sha256.New(),
         rng,
         PublicKey,
         bytes,
         nil)
    if err != nil {
      return encryptedBytes,err
    }
    encryptedBytes = append(encryptedBytes, encryptedByte...)
  }

  // Returns file encrypted
  return encryptedBytes,nil
}

I tried doing that but it returns the same error. I'll add the encryption function as well. — Michael Canady, Nov 16 '20 at 02:43
what is ur split function and how did you generate private/public key? — nguyenhoai890, Nov 16 '20 at 04:38
Does this answer your question? (don't mind the language difference) https://stackoverflow.com/a/35686847/1816580 — Artjom B., Nov 16 '20 at 06:13
It would be better to use [hybrid encryption](https://en.wikipedia.org/wiki/Hybrid_cryptosystem) instead of RSA in ECB mode. This is faster and less error prone — Artjom B., Nov 16 '20 at 06:17
Take a look at the size of your encrypted data vs the data in clear. Notice that it have grown in size. You don't account for this in your decrypt, but instead just assume the blocks are 200 bytes ... RSA is not suited for bulk encryption — Ebbe M. Pedersen, Nov 16 '20 at 10:11

score 1 · Answer 1 · edited Aug 03 '21 at 05:17

The step for rsa.EncryptOAEP() should be no longer than :

publicKey.Size() - 2*hash.Size() - 2

You can use publicKey.Size() - 2*hash.Size() - 2 as step of rsa.EncryptOAEP()

No matter the length of step, rsa.EncryptOAEP() function always produce fixed length encrypted data, the fixed length is publicKey.Size().

so, the step for rsa.DecryptOAEP() is :

publicKey.Size()

Please see : RS256 message too long for RSA public key size - error signing JWT

receiving crypto/rsa: decryption error when decrypting a file

1 Answers1