How to get publicKey in RSA_encrypt key-pair generation algorithm in STRING format in flutter

Question

I am currently working on encryption in my flutter app wherein I am using RSA key-pair generator to get public and private key using the following code-

import 'package:rsa_encrypt/rsa_encrypt.dart';
import 'package:pointycastle/api.dart' as crypto;

//Future to hold our KeyPair
Future<crypto.AsymmetricKeyPair> futureKeyPair;

//to store the KeyPair once we get data from our future
crypto.AsymmetricKeyPair keyPair;

Future<crypto.AsymmetricKeyPair<crypto.PublicKey, crypto.PrivateKey>> getKeyPair()
{
var helper = RsaKeyHelper();
return helper.computeRSAKeyPair(helper.getSecureRandom());
}

Now I want to get the keyPair.publicKey in string format but if i print keyPair.publicKey, it shows "Instance of RSA publicKey" . How can I get it in string format??

Maarten Bodewes · Accepted Answer · 2021-01-23 21:26:03Z

2

It is always best to use standardized formats when saving public keys. For RSA public keys you can store them in layers, much like a Matroesjka doll.

Encode the public key in the ASN.1 / DER format specified in the PKCS#1 RSA standard;
Encode that public key in a format called SubjectPublicKeyInfo which is part of the X.509 specifications - it indicates that this is indeed an RSA key;
Apply so called PEM "ASCII armor", which consists of a header & footer line indicating the generic SubjectPublicKeyFormat (just PUBLIC KEY), with a multi-line base 64 encoding of the public key from step 2 in between.

Sounds like a lot of work, but if you look here you'll find handy methods called encodePublicKeyToPem and parsePublicKeyFromPem that do these 3 steps for you (it actually does both 1 and 2 in the same function, which is a bit of a shame but not that important).

These keys are rather portable and are also usable by e.g. OpenSSL or PGP.

edited Jan 23, 2021 at 21:26

answered Jan 22, 2021 at 21:52

Maarten Bodewes

94.6k15 gold badges169 silver badges289 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Sakshi Pandey Over a year ago

Thank you so much for the answer! I found similar implementations for "encodePrivateKeyToPemPKCS1' mentioned in the docs https://pub.dev/packages/rsa_encrypt as the GitHub link of methods that you had sent in https://www.programmersought.com/article/18664973041/. That GitHub link of methods can also be used for reversing the instace->string :) conversion.

Alberto M Over a year ago

everyone refers to this gist but it's broken...

Maarten Bodewes Over a year ago

@AlbertoM Thanks for notifying me, but please explain why you think it is broken so we can investigate!

Andrewcpu Over a year ago

RsaKeyHelper().generateKeyPair(); throws Unhandled exception: type 'AsymmetricKeyPair<PublicKey, PrivateKey>' is not a subtype of type 'AsymmetricKeyPair<RSAPublicKey, RSAPrivateKey>'

Andrewcpu Over a year ago

Since the aforementioned Gist no longer works, I recommend using raw.githubusercontent.com/Ephenodrom/Dart-Basic-Utils/master/… and raw.githubusercontent.com/Ephenodrom/Dart-Basic-Utils/master/… @AlbertoM

Collectives™ on Stack Overflow

How to get publicKey in RSA_encrypt key-pair generation algorithm in STRING format in flutter

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related