OpenSSL.NET decrypting with GOST using c#

Question

I have an encrypted base64 file "PersonalCodes.txt" and a private key to it "private.key". The key is in .pem (---begin private key -- etc.) and is encrypted with -gost89. I need to use an OpenSSL.NET for this (apparently System.Security.Cryptography have no support on .pem keys) For the simple openssl client , the commands will be:

base64 -d -in "PersonalCodes.txt" -out  "PersonalCodesOUT.txt"

smime -decrypt -in "PersonalCodesOUT.txt" -inform der -inkey "private.key" -out "DecryptedCodes.txt"

First one is decrypting from base64 -ok. easy. Next one is decrypting with gost89 key.

As for the .NET - honestly , i'm completely frustrated. I added a reference to an openssl wrapper, and found an example how to get a key from file :

  byte[] b = System.IO.File.ReadAllBytes(@"D:\private.key");
                    OpenSSL.Core.BIO bio = new OpenSSL.Core.BIO(b);
   OpenSSL.Crypto.CryptoKey key = OpenSSL.Crypto.CryptoKey.FromPrivateKey(bio, "");

But this gives me an exception : unsupported private key algorithm According to google - i need to help openssl to see gost89 How should i do that in c#?

Moreover, can anyone help me with a the last command - decrypting with a private key in openssl.net? Ty...

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Found this implementation of the gost89 : https://github.com/embedthis/packages/blob/master/openssl/openssl-1.0.1c/engines/ccgost/gost89.c

However it also doesnt give a function to decrypt a file with key...