C#.NET 国密 SM2 公钥证书从文本转换

先前的 Util 是直接从文件中转换的

https://www.cnblogs.com/runliuv/p/15079404.html

public static AsymmetricKeyParameter GetPublickeyFromX509File(FileInfo file)

加一个方法，从文本字符串转换。

SM2 公钥证书文本：

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

处理方法（nuget上下载最新BouncyCastle.Crypto.dll）：

 public static AsymmetricKeyParameter GetPublickeyFromX509String(string publicKeyCert)
        {
                //还原完整文本格式
                publicKeyCert = StrToPubCert(publicKeyCert);

                byte[] bytesCerContent = System.Text.Encoding.UTF8.GetBytes(publicKeyCert);
                //需要完整文本格式才能解析
                X509Certificate certificate = new X509CertificateParser().ReadCertificate(bytesCerContent);
                return certificate.GetPublicKey();
        }

/// <summary>
        /// 转为完整格式
        /// </summary>
        /// <param name="pubKeyStr"></param>
        /// <returns></returns>
        public static string StrToPubCert(string publicKeyCert)
        {
            //去除意外字符
            publicKeyCert = publicKeyCert.Replace("-----BEGIN CERTIFICATE-----", "").Replace("-----END CERTIFICATE-----", "").Replace("\r", "").Replace("\n", "").Trim();

            //完整
            string rn = "\n";
            StringBuilder sbKey = new StringBuilder(publicKeyCert);
            int nKeyLen = sbKey.Length;      //sbKey为base64编码的公钥字符串
            for (int i = 64; i < nKeyLen; i += 64)
            {

                sbKey.Insert(i, rn);

                i++;
            }
            sbKey.Insert(0, "-----BEGIN CERTIFICATE-----" + rn);
            sbKey.Append(rn + "-----END CERTIFICATE-----" + rn);
            string all_key_str = sbKey.ToString();

            return all_key_str;
        }

public X509Certificate ReadCertificate(byte[] input)，这个方法需要读取完整公钥格式的字符串，即带“-----BEGIN CERTIFICATE-----”和“"-----END CERTIFICATE-----”，否则转换不了。

文本转byte[] 时，使用System.Text.Encoding.UTF8.GetBytes()，而非Convert.FromBase64String()。