Nodejs `crypto.publicEncrypt` would not take public key generated by `ssh-keygen rsa`

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I used ssh-keygen rsa to generate an RSA keypair. The generated public key looks like this:

ssh-rsa AAAAB3NzaC1yc2EAAA...

When I try to use crypto in Node.js to encrypt a plain string,

const fs = require('fs');
const { publicEncrypt } = require('crypto');

const publicKey = fs.readFileSync('$path/to/publicKey').toString();

const encryptedToken = publicEncrypt(publicKey, Buffer.from('some plain string'));

it would give out the following error:

Error: error:0909006C:PEM routines:get_name:no start line
  at node:internal/crypto/cipher:78:12
  ...
 library: 'PEM routines',
 function: 'get_name',
 reason: 'no start line',
 code: 'ERR_OSSL_PEM_NO_START_LINE'

I am pretty new to cryptography and know only the general idea of public/private key encryption so would really appreciate any advice.

Edit:

I understand that crypto comes with method to generate key pairs, so I guess the question is more about why the ssh-rsa public key did not work here.

cryptojs node.js rsa
1 Answers

The posted public key is in OpenSSH format, which is not supported by NodeJS's crypto module, see documentation of crypto.publicEncrypt(key, buffer).

However, keys in OpenSSH format can be converted to formats that can be processed by NodeJS. This can be done via tools, e.g. ssh-keygen, or via libraries, e.g. node-sshpk.

Alternatively, keys can be generated directly in the required format using OpenSSL.

The following example uses the node-sshpk library and converts an OpenSSH private key to a PEM encoded PKCS8 key and an OpenSSH public key to a PEM encoded X.509/SPKI key. Both target formats are supported by NodeJS:

var sshpk = require('sshpk');
var crypto = require('crypto');

var privateKeyOpenSSH = `-----BEGIN OPENSSH PRIVATE KEY-----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=
-----END OPENSSH PRIVATE KEY-----`

var publicKeyOpenSSH = `ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQClwWZSI5vNh1GsqK9titTAnymVF+NyADWdcgekwqPirSXi9q2mth681LaXTrLZC/PVPG7sB5L37NPrvfNzPC8uAQ1xlvqVcDnvpcwuNyZmGc0pcNGdFX9QIyV5qN3B2FD3dgmmwZEJR7APyTog47ob8xUBDjffJsG4I8nKxMtY2TZW/8ndWsuQFYYuLA5RydmlHXv+abpAE6wtEC4GzWMQtyJ3Ul2lzzB9QuWtJ0J/D8/aZc6qm5MyFIQHLjIT5bpXngxIhXDgFrGWtwCYL9GHs4cmuG4gSaY5K2qYw97se8Uo1OOrMhICLJaY9ZbAj1S4/iDtvSnsYCTRgx68s9Cf whatever`;

// Convert
var privateKey = sshpk.parsePrivateKey(privateKeyOpenSSH, 'ssh');
var publicKey = sshpk.parseKey(publicKeyOpenSSH, 'ssh');
var privateKeyPkcs8 = privateKey.toBuffer('pkcs8');
var publicKeyX509 = publicKey.toBuffer('pkcs8');
console.log(privateKey.toString('ssh'));
console.log(publicKey.toString('ssh'));
console.log(privateKeyPkcs8.toString('utf8')); // -----BEGIN PRIVATE KEY-----...
console.log(publicKeyX509.toString('utf8')); // -----BEGIN PUBLIC KEY-----...

// Encrypt/Decrypt
var plaintext = Buffer.from('The quick brown fox jumps over the lazy dog', 'utf8');
var ciphertext = crypto.publicEncrypt(publicKeyX509.toString('utf8'), plaintext);
var decryptedText = crypto.privateDecrypt(privateKeyPkcs8.toString('utf8'), ciphertext);

console.log('Ciphertext, base64 encoded: ', ciphertext.toString('base64'));
console.log('Decrypted text: ', decryptedText.toString('utf8'));
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