KS.Fiks.Crypto 3.1.0

kryptering-dotnet

Common encryption and decryption logic required by various KS FIKS clients on the dotnet platform. All code is released under a MIT license

All crypto is performed using a portable C# version of the BouncyCastle library

Prerequisites

• This library targets .Net Core 3.1 as well as .Net Standard 2.1 and .Net Standard 2.0.
• A PEM file containing the BASE64 encoded public certificate to be used for encryption
• A PEM file containing the BASE64 encoded private key to be used for decryption

Example

Encryption

var encryptionService = EncryptionService.Create(/* public certificate */);
using (var encryptedOutStream = /* create out stream */)
using (var dataStream = /* the stream containing the unencrypted data */) 
{
    encryptionService.Encrypt(dataStream, encryptedOutStream);
}

Decryption

var decryptionService = DecryptionService.Create(/* private key */);
using (var encryptedDataInStream = /* stream containing the encrypted data */)
using (var decryptedOutStream = /* a stream to write the unencrypted data to */)
using (var decryptBufferStream = decryptionService.Decrypt(encryptedDataInStream))
{
    decryptBufferStream.CopyTo(decryptedOutStream);
}

Decryption with multiple private keys

The key-only DecryptionService.Create overloads try RSA-OAEP recipients when multiple private keys are supplied. Messages produced by this library include an RSA-OAEP recipient. With BouncyCastle 2.7 and later, a failed legacy RSA PKCS#1 v1.5 unwrap returns a random session key rather than throwing, so it cannot reliably identify the correct private key.

For automatic key selection with legacy-only messages, associate each private key with its matching certificate. The service matches CMS recipient identifiers (issuer and serial number, or subject key identifier) before opening the decrypted stream:

var decryptionService = DecryptionService.Create(new[]
{
    new DecryptionKey(oldCertificate, oldPrivateKey),
    new DecryptionKey(currentCertificate, currentPrivateKey)
});

The certificate and private key parameters are BouncyCastle X509Certificate and AsymmetricKeyParameter instances. Key/certificate mismatches are rejected when creating a DecryptionKey. No certificate trust or validity check is performed by this association. If no certificate matches a recipient, decryption throws a CmsException. For legacy-only messages without certificates, select a single private key explicitly; supplying multiple unassociated keys throws a CmsException. Decrypted content remains streamed; it is not buffered to guess which key succeeded.