Java RSA Decryption - Bad Padding Exception

Question

This is my code so far. Every time I run it, I receive a bad padding exception only while trying to decrypt. If I swap the use of my private and public keys it still throws the same exception in decrypt. This makes me believe that it is an issue with the Decrypt itself. Any thoughts on what I am doing wrong?

try {
            Cipher Bob_Message_Verify = Cipher.getInstance("RSA");    
            Bob_Message_Verify.init(Cipher.DECRYPT_MODE, Alice_Pair_I.getPublic());
            Bob_Verification_Message_Decrypt = (Bob_Message_Verify.doFinal(Bob_Verification_Message_Encrypt));

        }catch(NoSuchAlgorithmException e)
        {
            throw new OTPException("Not RSA");
        }
        catch(IllegalBlockSizeException e)
        {
            throw new OTPException("Wrong Block Size");
        }
        catch(NoSuchPaddingException e)
        {
            throw new OTPException("No Padding");
        }
        catch(InvalidKeyException e)
        {
            throw new OTPException("Invalid Key");
        }
        catch(BadPaddingException e)
        {
            throw new OTPException("Bad Padding");
        }

bad padding exception always come when you decrypt with some different java version than the java with which you encrypt it — sparsh610
– sparsh610, Commented May 8, 2020 at 14:38
welcome to stackoverflow. Take a tour and get your first badge-stackoverflow.com/tour — Hemant
– Hemant, Commented May 8, 2020 at 14:38
Your question is impossible to answer without more details, such as how the message was encrypted. Note that Java has a Signature API which is what you should be using for signing/verifying. Also, never use defaults in crypto. In your case, your transformation string "RSA" does not specify the mode and padding and thus relies on defaults. Different providers will use different defaults. — President James K. Polk
– President James K. Polk, Commented May 8, 2020 at 17:29

Maarten Bodewes · Accepted Answer · 2020-05-10 23:07:56Z

1

The reason that you are getting an error is that you are trying to verify with a Cipher. You need to use a Signature instance of that. Note that the specifics of signature generation are rather different from a cipher. Signature verification conversely is not the same as decryption with the public key.

answered May 10, 2020 at 23:07

Maarten Bodewes

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