crypto.privateDecrypt cannot decrypt message

[Nolaan]

• Version: v8.11.3
• Platform: Linux x86_64
• Subsystem:

I'm trying to encrypt/decrypt data using a rsa key but the process fails somehow with this message :

Error: error:04099079:rsa routines:RSA_padding_check_PKCS1_OAEP_mgf1:oaep decoding error

Code :

var childProcess = require('child_process');
var crypto = require('crypto');

var pk;
var mess_chiffre;

var sign = function () {
 var buf = new Buffer("Coucou c'est relou!!!");
 var sig = crypto.privateEncrypt(pk,buf);
 mess_chiffre = sig.toString('hex');
 console.log("Signed : ", mess_chiffre);
};


var decrypt = function () {
 var buff = new Buffer(mess_chiffre,'hex')
 console.log('Buffer : ',buff)
 console.log('decrypting withh pk: ')
 console.log(pk)
 var mess = crypto.privateDecrypt(pk,buff)
 console.log(mess)
};


childProcess.exec('openssl rsa -in private.key', {},
 function (err, stdout, stderr) {
 if (err) throw err;
 pk = stdout; // Save in memory for later use
 sign();
 decrypt();
});

[addaleax]

@nodejs/crypto

[tniessen]

Just so we are on the same page: Why are you trying to use privateDecrypt after applying privateEncrypt? That's not how asymmetric encryption works.

[mscdex]

Yes, either privateEncrypt() needs to be publicEncrypt() or privateDecrypt() needs to be publicDecrypt().

[mscdex]

Also, in the future please ask help questions such as this on the nodejs/help issue tracker.

[addaleax]

I do think this should be mentioned in the docs, ideally with an example of how to do it “right”?

[Nolaan]

@tniessen So please provide a working example. From the docs I couldn't neither with publicEncrypt/privateDecrypt or otherwise.

[tniessen]

const crypto = require('crypto');

const privateKey = `-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----`;

const publicKey = `-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCqGKukO1De7zhZj6+H0qtjTkVxwTCpvKe4eCZ0
FPqri0cb2JZfXJ/DgYSF6vUpwmJG8wVQZKjeGcjDOL5UlsuusFncCzWBQ7RKNUSesmQRMSGkVb1/
3j+skZ6UtW+5u09lHNsj6tQ51s1SPrCBkedbNf0Tp0GbMJDyR4e9T04ZZwIDAQAB
-----END PUBLIC KEY-----`;

const plaintext = Buffer.from('Hello world!', 'utf8');

// This is what you usually do to transmit encrypted data.
const enc1 = crypto.publicEncrypt(publicKey, plaintext);
const dec1 = crypto.privateDecrypt(privateKey, enc1);
console.log(dec1.toString('utf8'));

// This works as well.
const enc2 = crypto.privateEncrypt(privateKey, plaintext);
const dec2 = crypto.publicDecrypt(publicKey, enc2);
console.log(dec2.toString('utf8'));

[Nolaan]

Thanks! But why would the private key be able to decrypt anything? Isn't it suppose to be just an encrypting key, the one you send to people?

[Nolaan]

I found the answer. TIL : https://security.stackexchange.com/questions/9957/can-i-use-a-private-key-as-a-public-key-and-vice-versa

[tniessen]

@Nolaan That's what the private key is usually for, yes, and publicEncrypt / privateDecrypt is much more common than the other pair of functions. However, some asymmetric ciphers (such as RSA) can be used in the other way as well.

[Nolaan]

Ok, I've lost it a bit in the docs because I saw :

Because RSA public keys can be derived from private keys, a private key may be passed instead of a public key.

So I thought I could just use the private key for symmetric encryption (encrypt/decrypt).

[tniessen]

@Nolaan You can by passing the private key to publicDecrypt / publicEncrypt.