CODEWITHSUNDEEP
goencryption
Michael Canady
Michael Canady

Reputation: 56

receiving crypto/rsa: decryption error when decrypting a file

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
}

Upvotes: 1

Views: 2918

Answers (1)

bluesky2015
bluesky2015

Reputation: 37

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

Upvotes: 1

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