CODEWITHSUNDEEP
c#rsabouncycastleder
SupaDupa
SupaDupa

Reputation: 181

Export RSA Public Key in DER Format and decrypt data

I need to get the bytes of my RSA Public Key in the DER format and send this key to an API. This API will then send me something encrypted using this Public Key back and i need to decrypt it.

First problem, it seems that C# doesn't have the ability to export RSA Keys in the DER Format. So it seems i have to rely on a 3rd party package like BouncyCastle. I also found a way to generate and export my Public Key in the DER Format with this package:

var generator = new RsaKeyPairGenerator();
generator.Init(new KeyGenerationParameters(new SecureRandom(), 2048));
var keyPair = generator.GenerateKeyPair();
var publicKeyParam = (RsaKeyParameters)keyPair.Public;
var publicKey = SubjectPublicKeyInfoFactory.CreateSubjectPublicKeyInfo(publicKeyParam).GetDerEncoded();

So now i only had to Base64 encode those bytes and send it to the API and the API is happy. But now i'm stuck trying to figure out how i can decrypt the dat i received. First of all i decoded the base64 string and now i'm stuck with the bytes of the data. I can get the private key from the BouncyCastle "thing", but i cant seem to convert it to RsaCryptoServiceProvider correctly and the BouncyCastle documentation is kind of weird. If anyone has an idea or another approach i would be more than happy.

Upvotes: 2

Views: 2284

Answers (1)

SupaDupa
SupaDupa

Reputation: 181

Based on the comments i came up with this solution:

var rsa = new RSACryptoServiceProvider(2048); // my rsa to decrypt and encrypt data

var publicKeyParam = DotNetUtilities.GetRsaPublicKey(rsa.ExportParameters(false));
var publicKey = SubjectPublicKeyInfoFactory.CreateSubjectPublicKeyInfo(publicKeyParam).GetDerEncoded(); // my exported public key in DER format

Thanks alot James K Polk!

Upvotes: 2

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