C# .NET “公钥证书” （.cer .pem）转换为 RSACryptoServiceProvider 对象。导出“公钥”

“公钥证书” .cer 文件是直接可以用X509Certificate2 对象来读取的，但 .cer 文件不便于存储。

“公钥证书” .pem 文件内容如下：

string pemPublicCert = Path.Combine(Application.StartupPath, "CCQTGBtest.pem");

            string base64X509Cert = "";//"公钥证书"字符串

            /*

             -----BEGIN CERTIFICATE-----

MIICnzCCAggCCQDbr9OvJHgzmDANBgkqhkiG9w0BAQUFADCBkzELMAkGA1UEBhMC

RUUxETAPBgNVBAgMCEhhcmp1bWFhMRAwDgYDVQQHDAdUYWxsaW5uMREwDwYDVQQK

DAhFZXRhc29mdDERMA8GA1UECwwIYmFua2xpbmsxFjAUBgNVBAMMDXBhbmdhbGlu

ay5uZXQxITAfBgkqhkiG9w0BCQEWEmVldGFzb2Z0QG9ubGluZS5lZTAeFw0xNDEy

MjQxNjI1MjdaFw0zNDEyMTkxNjI1MjdaMIGTMQswCQYDVQQGEwJFRTERMA8GA1UE

CAwISGFyanVtYWExEDAOBgNVBAcMB1RhbGxpbm4xETAPBgNVBAoMCEVldGFzb2Z0

MREwDwYDVQQLDAhiYW5rbGluazEWMBQGA1UEAwwNcGFuZ2FsaW5rLm5ldDEhMB8G

CSqGSIb3DQEJARYSZWV0YXNvZnRAb25saW5lLmVlMIGfMA0GCSqGSIb3DQEBAQUA

A4GNADCBiQKBgQDCi9usnv8rJLBeBgHhbM/80zPUOlkuH0uYrdzj/zxQSZS0QEoH

yVvosEWqO34+17CzQ0sc34kzK5qhLws7AKetjLH7cpgmVH5YnQxKgZ2a5I5mpj02

v9rjwDSKX2ZDXCeRUdnZa26beMcX/i1C9jxk9tpE2NWud910yHPRpnAQFwIDAQAB

MA0GCSqGSIb3DQEBBQUAA4GBAFmlXa8NkR2OP0bC0EapmCaoObUG2WOi6Fhl2dBB

PInJq6tzv+YtMbaIAPANo1EzBeBcQTRvxgGIrqE/JJkjDhOvwxjdNcxp7Mt+7hkk

PI55KkKAfOeE0ss0EUcCdnyCGAXdhJfUCxJydg0PaVpE70FXUcLZcZXfT968mDOC

NpaS

-----END CERTIFICATE-----

             */

            using (FileStream fs = new FileStream(pemPublicCert, FileMode.Open, FileAccess.Read))

            {

                using (StreamReader sr = new StreamReader(fs))

                {

                    base64X509Cert = sr.ReadToEnd().Trim();

                }

            }

            //提取纯字符串

            base64X509Cert = base64X509Cert.Replace("-----BEGIN CERTIFICATE-----", "").Replace("-----END CERTIFICATE-----", "").Replace("\r", "").Replace("\n", "");

            //https://stackoverflow.com/questions/27642180/how-to-create-public-key-from-certificate

            //转换为“公钥”对象

            var derCert = Convert.FromBase64String(base64X509Cert);

            var x509 = new X509Certificate2(derCert);

            RSACryptoServiceProvider rsa = (RSACryptoServiceProvider)x509.PublicKey.Key;

            MessageBox.Show(rsa.ToXmlString(false));

            //Console.WriteLine(rsa.ToXmlString(false));

拿到RSACryptoServiceProvider  对象 （公钥）后，就可以验证签名了，或加密。

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