ContentCryptoScheme encryptionSchemeOf(Map<String,String> instructionFile) {
        if (instructionFile != null) {
            String cekAlgo = instructionFile.get(Headers.CRYPTO_CEK_ALGORITHM);
            return ContentCryptoScheme.fromCEKAlgo(cekAlgo);
        }
        ObjectMetadata meta = s3obj.getObjectMetadata();
        Map<String, String> userMeta = meta.getUserMetadata();
        String cekAlgo = userMeta.get(Headers.CRYPTO_CEK_ALGORITHM);
        return ContentCryptoScheme.fromCEKAlgo(cekAlgo);
    }
Returns the original crypto scheme used for encryption, which may
differ from the crypto scheme used for decryption during, for example,
a range-get operation. 

@param instructionFile
           the instruction file of the s3 object; or null if there is
           none.
aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/internal/crypto/v2/S3ObjectWrapper.java