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I am trying to implement RSA encryption which is able to do the following:

  • accept a string value as an input to encrypt using a public key
  • return the encrypted cipher as string
  • accept the encrypted cipher as an input to decrypt using a private key
  • return the original value, decrypted

I am able to get the encryption/decryption working if I directly decrypt the byte array returned by the encryption, but annot seem to get it to work if I parse the byte array to a String and then back to bytes again.

The following code does work:

cipher.init(Cipher.ENCRYPT_MODE, pubKey);
byte[] cipherBytes = cipher.doFinal(input);
System.out.println("cipher: " + new String(cipherBytes));
returnValue += new String(cipherBytes);

cipher.init(Cipher.DECRYPT_MODE, privKey);
byte[] plainText = cipher.doFinal(cipherBytes);
System.out.println("plain : " + new String(plainText));

The following code does NOT work:

byte[] cipherBytes = cipher.doFinal(input);
System.out.println("cipher: " + new String(cipherBytes));
returnValue += new String(cipherBytes);

String cipherText = new String(cipherBytes);
byte[] reCipherBytes = cipherText.getBytes();

cipher.init(Cipher.DECRYPT_MODE, privKey);
byte[] plainText = cipher.doFinal(reCipherBytes);
System.out.println("plain : " + new String(plainText));

Can anyone advise what I'd need to do to get the second version to work successfully?

Niall
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1 Answers1

5

I think your problem is because of the default java ecoding/deconding charset when converting a byte array to string and vice-versa.

I have debugged your code and reCipherBytes has not the same length as cipherBytes, that is why the second code blocks throws an exception.

I recomend you to use base64 encoding for transforming cipherBytes into a string.

    cipher.init(Cipher.ENCRYPT_MODE, publicKey);
    byte[] cipherBytes = cipher.doFinal(input);
    System.out.println("cipher: " + new String(cipherBytes));
    String returnValue = new String(cipherBytes);

    String cipherText = Base64.getEncoder().encodeToString(cipherBytes);
    byte[] reCipherBytes = Base64.getDecoder().decode(cipherText);

    cipher.init(Cipher.DECRYPT_MODE, privateKey);
    byte[] plainText = cipher.doFinal(reCipherBytes);
    System.out.println("plain : " + new String(plainText));

This code fragment should work

jmarques
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