Problem replacing deprecated method with suggested replacement

[ericlw]

Using KeyGenParameterSpec.Builder makes keys unable to decrypt, any thoughts?

             if(Build.VERSION.SDK_INT <= 18) {
                    Calendar start = Calendar.getInstance();
                    Calendar end = Calendar.getInstance();
                    end.add(Calendar.YEAR, 1);

                    KeyPairGeneratorSpec spec = new KeyPairGeneratorSpec.Builder(this)
                            .setAlias(alias)
                            .setSubject(new X500Principal("CN=Sample Name, O=Android Authority"))
                            .setSerialNumber(BigInteger.ONE)
                            .setStartDate(start.getTime())
                            .setEndDate(end.getTime())
                            .build();

                    generator.initialize(spec);
                }
                else {

                    generator.initialize(new KeyGenParameterSpec.Builder
                            (alias, KeyProperties.PURPOSE_SIGN)
                            .setDigests(KeyProperties.DIGEST_SHA256)
                            .setSignaturePaddings(KeyProperties.SIGNATURE_PADDING_RSA_PKCS1)
                            .build());

                }

                KeyPair keyPair = generator.generateKeyPair();

http://stackoverflow.com/questions/36802523/keypairgeneratorspec-replacement-with-keygenparameterspec-builder-equivalents