Swift与C#实现Diffie Hellman密钥交换时共享密钥不一致

我正在尝试在iOS（Swift）应用与ASP.NET 8 Core Web服务器间实现Diffie-Hellman密钥交换，但双方生成的共享密钥始终不一致。

已尝试的操作 #

• 确认iOS发送至服务器的公钥在接收后完全匹配；
• 确认服务器发送至iOS的公钥在接收后完全匹配；
• 尝试统一双方密钥格式（可能仍存在格式错误）。

工作流程 #

1. iOS应用生成密钥对，将公钥发送至服务器；
2. 服务器推导共享密钥，再将自身公钥返回给应用；
3. iOS应用使用服务器公钥推导共享密钥，但双方结果不匹配。

Swift 代码（基于CryptoKit，测试环境iOS 17.6+）

class HandshakeHelper
{
    // 创建密钥对
    static func createKeyPairs() -> [String]
    {
        let privateKey = P256.KeyAgreement.PrivateKey()
        let privateKeyBase64 = privateKey.derRepresentation.base64EncodedString()
        let publicKeyBase64 = privateKey.publicKey.derRepresentation.base64EncodedString() // DER编码（X.509格式）
        return [privateKeyBase64, publicKeyBase64]
    }
    
    // 推导共享密钥：使用己方私钥和对方公钥生成共享密钥
    static func deriveSharedSecret(ourPrivateKeyBase64: String, receivedPublicKeyBase64: String) -> String?
    {
        guard let privateKeyData = Data(base64Encoded: ourPrivateKeyBase64),
              let receivedPublicKeyData = Data(base64Encoded: receivedPublicKeyBase64) else
        {
            print("无效的密钥数据")
            return nil
        }
        
        do
        {
            // 重建己方私钥和接收的公钥
            let privateKey = try P256.KeyAgreement.PrivateKey(derRepresentation: privateKeyData)
            let receivedPublicKey = try P256.KeyAgreement.PublicKey(derRepresentation: receivedPublicKeyData) // DER编码
            
            // 推导共享密钥
            let sharedSecret = try privateKey.sharedSecretFromKeyAgreement(with: receivedPublicKey)
            
            // 返回Base64格式的共享密钥
            return sharedSecret.withUnsafeBytes { Data($0).base64EncodedString() }
        } catch
        {
            print("推导共享密钥出错: \(error)")
            return nil
        }
    }
}

.NET 8 代码（基于System.Security.Cryptography）

public class HandshakeHelper
{
    // 创建密钥对
    public static List<string> CreateKeyPairs()
    {
        using var ecdh = ECDiffieHellman.Create(ECCurve.NamedCurves.nistP256);
        var privateKey = Convert.ToBase64String(ecdh.ExportECPrivateKey()); // PKCS#8格式
        var publicKey = Convert.ToBase64String(ecdh.ExportSubjectPublicKeyInfo()); // X.509格式
        File.WriteAllText("ecdh_priv.key", privateKey);
        File.WriteAllText("ecdh_pub.key", publicKey);
        return new List<string> { privateKey, publicKey };
    }

    // 推导共享密钥：使用己方私钥和对方公钥生成共享密钥
    public static string DeriveSharedSecret(string ourPrivateKeyBase64, string receivedPublicKeyBase64)
    {
        var privateKeyBytes = Convert.FromBase64String(ourPrivateKeyBase64);
        var receivedPublicKeyBytes = Convert.FromBase64String(receivedPublicKeyBase64);

        using var ecdh = ECDiffieHellman.Create(ECCurve.NamedCurves.nistP256);
        ecdh.ImportECPrivateKey(privateKeyBytes, out _); // 导入己方私钥

        using var receivedPublicKey = ECDiffieHellman.Create();
        receivedPublicKey.ImportSubjectPublicKeyInfo(receivedPublicKeyBytes, out _); // 导入接收的公钥

        // 推导共享密钥
        var sharedSecret = ecdh.DeriveKeyMaterial(receivedPublicKey.PublicKey);
        return Convert.ToBase64String(sharedSecret); // 返回Base64格式的共享密钥
    }
}

内容的提问来源于Stack Exchange，提问作者John Rams