在.NET上使用RSA私钥签名字符串？

byte[] plaintext = System.Text.Encoding.UTF8.GetBytes("AAAAAAAAAAAAA"); TextReader trCer = new StreamReader(@"AA.key"); //key in PEM format PemReader rdCer = new PemReader(trCer); AsymmetricCipherKeyPair o = rdCer.ReadObject() as AsymmetricCipherKeyPair; ISigner sig = SignerUtilities.GetSigner("MD5WithRSAEncryption"); sig.Init(true, o.Private); sig.BlockUpdate(plaintext,0,plaintext.Length); Byte[] signature = sig.GenerateSignature(); string signatureHeader = Convert.ToBase64String(signature); Console.WriteLine(signatureHeader); 

如何使用DER格式的密钥？ 我正在使用库BouncyCastle.Crypto.dll

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