Create .pem file for public key RSA encryption C# .net

c# encryption rsa public-key-encryption encryption-asymmetric

15,635

Solution 1

First off, a so-called .pem file is not really a fixed specification or format. Several different kinds of distinct file formats are generally described as "PEM" files. When the SSLeay (now OpenSSL) project needed to produce a base64 encoded output file containing key information they borrowed formatting concepts from the old Privacy-Enhanced Mail RFCs 1421-1424 and they added the extension .pem to the end of these files. But such a file may contain public keys, private keys, certificate requests, certificates, certificate lists, and so on. Each is different. So if all you're told is to produce a .pem file you're going to have to guess what's really needed.

The easiest way to write such files is to use the Bouncycastle C# library. The package Org.BouncyCastle.OpenSsl contains a number of utilities including a PemWriter class that should help you.

Solution 2

Recently I need to save PublicKey and PrivateKey generated in my C# application to file, and works with it later. I use for this purpose such library as CSharp-easy-RSA-PEM.

It is very simple and quick solution, so I will recommend this library to other guys.

I use following code to get PublicKey as string (and save it to pem file in format Base64):

string publicKeyStr = Crypto.ExportPublicKeyToX509PEM(_cryptoServiceProvider);

it returns something like this:

And I use following code to get PrivateKey as string:

string privateKeyStr = Crypto.ExportPrivateKeyToRSAPEM(_cryptoServiceProvider);

it returns something like this:

Then you can use

RSACryptoServiceProvider publicX509key = Crypto.DecodeX509PublicKey(publicKeyStr);
RSACryptoServiceProvider privateRSAkey = Crypto.DecodeRsaPrivateKey(privateKeyStr);

to restore saved keys back to RSACryptoServiceProvider.

So, if someone need to resolve similar issue, you can just download this library, go to Solution Explorer -> (Right click on your project) -> Add -> Reference -> Overview in your Visual Studio to add this library in your project, and add using CSharp_easy_RSA_PEM; where you need it :)

15,635

Author by

Yasser-Farag

Updated on June 24, 2022

Comments

Yasser-Farag almost 2 years

I want to create .pem file for the public key generated by this method

public static Tuple<string, string> CreateKeyPair()
{
    CspParameters cspParams = 
        new CspParameters { 
            ProviderType = 1 /* PROV_RSA_FULL */ 
        };

    RSACryptoServiceProvider rsaProvider = 
        new RSACryptoServiceProvider(1024, cspParams);

    string publicKey = Convert.ToBase64String(rsaProvider.ExportCspBlob(false));
    string privateKey = Convert.ToBase64String(rsaProvider.ExportCspBlob(true));

    return new Tuple<string, string>(privateKey, publicKey);
}

Because I was generating this key for mobile application and they can not read it, they requested .pem file instead of public key as string

Please advice,

V. Panchenko almost 7 years

Don't use Org.BouncyCastle.OpenSsl, because it has no examples and very bad documentation for C#! I worked under the same problem, and this library really helps me: https://github.com/jrnker/CSharp-easy-RSA-PEM. It has good examples and you can solve your problem using only one line (instead of implement some interfaces from BouncyCastle)!
President James K. Polk almost 7 years

@V.Panchenko: Thanks for your comment. Please consider writing an answer to this question with the one-liner as an example.
President James K. Polk almost 7 years

Looks like a nice solution.
l3dx about 5 years

CSharp-easy-RSA-PEM is GPL3 licensed, so you can't use it unless your project is GPL too. BouncyCastle on the other hand is MIT
Jared Thirsk over 4 years

I'd give it an upvote if it had a liberal license, but alas, it is GPL.