Reading public and private key from stored files in node js - node.js

Question

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

Answer 1

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:
-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
rsa_publickey_2048.pem:
-----BEGIN RSA PUBLIC KEY-----
MIIBCgKCAQEAmbeKgSAwVe0nZ84XlbDhMkUDjx1C0duA16MkzHTg1uh9SouOKK0e
3gPtTJ9LssaHlXSYhjpMDMWGO6ujd85XRosI2u9eSMNRYY25AQuBriSTVdi9BHqW
AuWuo6VuvTrkgWTL69vNWvLXTOkTiIyrgnhiavjNvm4UVy2AcO2Y3ER+dKgJpQAY
lEP1jvuQuf6dfNdSBoN0DZbxZXYbQqoA9R/u0GZHCXY+r8A54RejG34pnnuHkoyR
OZz5H9LbKGOiaETryornQ1TRvB/p9tgIoCJFI71WsKsqeWQPG3Ymg/FoEWXNY0yo
pZEjpkZa3tU+hrOmAFIRg+/bedKfjYFi/QIDAQAB
-----END RSA PUBLIC KEY-----

Answer 2

There's potentially a few issues with your code or the encryption key you're using:
You're using fs.read incorrectly as Node is asynchronous and it needs a callback function to properly read the file.
The encryption key you're using is formatted incorrectly for crypto.publicEncrypt. You must have the proper RSA headers.
I modified your code to use fs.readFile properly instead in the standard Node callback form, and here's an example encryption key in the correct RSA format to use:
var path = require('path');
var crypto = require('crypto');
var fs = require('fs');
var encryptStringWithRsaPublicKey = function(toEncrypt, relativeOrAbsolutePathToPublicKey, callback) {
var absolutePath = path.resolve(relativeOrAbsolutePathToPublicKey);
fs.readFile(absolutePath, 'utf-8', (err, publicKey) => {
// The value of `publicKey` is in the callback, not the return value
console.log(publicKey);
var buffer = Buffer.from(toEncrypt);
var encrypted = crypto.publicEncrypt(publicKey, buffer);
if (err) {
callback(err);
} else {
callback(null, encrypted.toString("base64"));
}
});
};
encryptStringWithRsaPublicKey('hello world', 'test.pub', (err, encrypted) => {
// If you're using a callback in a function,
// the original function must have a callback as well
console.log(encrypted);
});
Example encryption key at test.pub (must have the RSA headers as shown below):
-----BEGIN RSA PUBLIC KEY-----
MIIBCgKCAQEA+xGZ/wcz9ugFpP07Nspo6U17l0YhFiFpxxU4pTk3Lifz9R3zsIsu
ERwta7+fWIfxOo208ett/jhskiVodSEt3QBGh4XBipyWopKwZ93HHaDVZAALi/2A
+xTBtWdEo7XGUujKDvC2/aZKukfjpOiUI8AhLAfjmlcD/UZ1QPh0mHsglRNCmpCw
mwSXA9VNmhz+PiB+Dml4WWnKW/VHo2ujTXxq7+efMU4H2fny3Se3KYOsFPFGZ1TN
QSYlFuShWrHPtiLmUdPoP6CV2mML1tk+l7DIIqXrQhLUKDACeM5roMx0kLhUWB8P
+0uj1CNlNN4JRZlC7xFfqiMbFRU9Z4N6YwIDAQAB
-----END RSA PUBLIC KEY-----
As of 2020, there are also other ways of making the code cleaner, such as with using the Promises version of the fs module and async / await, though I wanted to keep this answer as simple as possible for now.