def sign(content): f = open('private_key.pem', 'rb') privateKey = f.read() key = RSA.importKey(privateKey) h = SHA.new(content) signer = PKCS1_v1_5.new(key) signature = signer.sign(h) return base64.b64encode(signature)改成C#写法

在C#中，可以使用BouncyCastle库来实现RSA签名。下面是将Python代码转换为C#代码的示例：

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Security;

public static string Sign(string content)
{
    var rsa = RSA.Create();
    var privateKeyText = File.ReadAllText("private_key.pem");
    var privateKeyBytes = Convert.FromBase64String(privateKeyText);
    var keyPair = (AsymmetricCipherKeyPair)new PemReader(new StringReader(privateKeyText)).ReadObject();
    var privateKey = (RsaPrivateCrtKeyParameters)keyPair.Private;

    rsa.ImportParameters(new RSAParameters
    {
        Modulus = privateKey.Modulus.ToByteArrayUnsigned(),
        Exponent = privateKey.PublicExponent.ToByteArrayUnsigned(),
        D = privateKey.Exponent.ToByteArrayUnsigned(),
        P = privateKey.P.ToByteArrayUnsigned(),
        Q = privateKey.Q.ToByteArrayUnsigned(),
        DP = privateKey.DP.ToByteArrayUnsigned(),
        DQ = privateKey.DQ.ToByteArrayUnsigned(),
        InverseQ = privateKey.QInv.ToByteArrayUnsigned()
    });

    var sha = SHA1.Create();
    var hash = sha.ComputeHash(Encoding.UTF8.GetBytes(content));
    var signature = rsa.SignHash(hash, HashAlgorithmName.SHA1, RSASignaturePadding.Pkcs1);

    return Convert.ToBase64String(signature);
}

注意，由于Python中的签名使用的是SHA-1算法，因此在C#中使用了相同的算法。如果要使用其他算法，则需要相应地更改。此外，还需要添加BouncyCastle库的引用。