Reading public and private key from stored files in node js

I wanted to encrypt and decrypt a message in node using public and private keys stored in my system. I was using the following java code to read the file and use the keys.

Java Code:

byte[]  keyBytes = Files.readAllBytes(new File(publicKeyFileName).toPath());
X509EncodedKeySpec spec = new X509EncodedKeySpec(keyBytes);
KeyFactory kf = KeyFactory.getInstance("RSA");
publicKey=kf.generatePublic(spec);

I am able to use the above java method without any issues to read the public key from file. However, I want to achieve similar functionality in node. I have tried using crypto for achieving the same but it gives me error while passing the key to publicEncrypt method.

Node:

var encryptStringWithRsaPublicKey = function(toEncrypt, relativeOrAbsolutePathToPublicKey) {
    var absolutePath = path.resolve(relativeOrAbsolutePathToPublicKey);
    var publicKey = fs.read(absolutepath, "utf-8");
    console.log(publicKey);
    var buffer = Buffer.from(toEncrypt);
    var encrypted = crypto.publicEncrypt(publicKey, buffer);
    return encrypted.toString("base64");
};

Error

internal/crypto/cipher.js:43
    return method(toBuf(key), buffer, padding, passphrase);
           ^

Error: error:0906D06C:PEM routines:PEM_read_bio:no start line

Please help. Thanks

Solution

Your problem is located in the file format you are actually using with Java. You probably save the private and the public in encoded ("byte array") to a file and rebuild the keys e.g. with X509EncodedKeySpec.

This format is not compatible to Node.JS and you have 3 ways to solve it:

a) you write the keys in Java with re neccessary format for usage in Node.JS

b) you write a converter in Node.JS to get the correct format

c) you convert the files with a tool like OPENSSL.

Here I show you the "c-way" as you are handling just one keypair and probably don't need a programatically solution.

Let's say you have two files with the private key ("rsa_privatekey_2048.der") and the public key ("rsa_publickey_2048.der").

In OPENSSL you are using the command line with

openssl rsa -inform der -in rsa_privatekey_2048.der -outform pem -out rsa_privatekey_2048.pem
openssl rsa -inform der -pubin -in rsa_publickey_2048.der -outform pem -RSAPublicKey_out -out rsa_publickey_2048.pem

to convert the files to their PEM-encoded formats.

Below you can find the two sample files I created.

rsa_privatekey_2048.pem:

rsa_publickey_2048.pem: