在C#中進行RSA解密，需要用RSACryptoServiceProvider，但是不支持OpenSSL格式的公鑰或者私鑰。
X509 公鑰
-----BEGIN PUBLIC KEY----- MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCRh7vKq7r6EhSg9y6iD38Vy08z umEJXhNTIGe8vRjdpE118Nu1cPRZ0AU9FbMIx8cnQtgCqGgW3DPDLj4VmlmdnJ8P cFHBBWgh85P1hicv8BQ0nLLjqezaBcS9EmO1C7zhdONVrvMFyHc1j76e+Fv+XfC6 CRvwKfqX+j5OMmWtowIDAQAB -----END PUBLIC KEY-----
非加密 PKCS#8 私鑰
-----BEGIN PRIVATE KEY----- MIICdgIBADANBgkqhkiG9w0BAQEFAASCAmAwggJcAgEAAoGBAJGHu8qruvoSFKD3 LqIPfxXLTzO6YQleE1MgZ7y9GN2kTXXw27Vw9FnQBT0VswjHxydC2AKoaBbcM8Mu PhWaWZ2cnw9wUcEFaCHzk/WGJy/wFDScsuOp7NoFxL0SY7ULvOF041Wu8wXIdzWP vp74W/5d8LoJG/Ap+pf6Pk4yZa2jAgMBAAECgYBxgvu5M4Xd9Che/S5Efe3UZAZd BK0Xj2dnWUlQ7/XrO3Kn4bydo4MUYqsTYE+LM7hlKUAvooe9/Pfq77DBTOlETcSJ fvZdL+mX5b3v8hnknWdpiyhfB2yaYbNTOUWMHboekwtqjP5C5yA5IObGcDFFPVZA /tRa50XNq3PATS1jIQJBAPi7U+zhFG/QKI4IlUYymwKlsa7ZMHJjXX8508ZxD0az YDfFsZEWquAdPPXj9lVlXD7uMBzewAx/gn2wTBLtr1sCQQCVyGRyTarXFaqdImEe +7/o6hCIdVvCBUuyIkd0WUPTkbizpUpUrzu9oy1UbvWlI2r4QqjoMh8eq05zlU+s J9VZAkEA6mDCzZSuiEoy3NvzpYksDguKagNYpoFBahBYoUaKKYn/Ya6VCu28KKEE f4PG7GMt0FLr3Vh8yYohsUQ9+xwjvwJAGDB8yFjytjmxjB75QF+35o2mjeMmJndk eig/EfM4mPp3scuH7ZU/OKkZsQEaesj1hZJ+ZMFzdSiFSvVaIJtuQQJAH3sXQ3DV EoeSW40TyYviq2K1pEpz9fGcS1TrjI+Yt1Mf0mvO6eupNZCfuhiAqJ5ZGRzTv1Pu G7pgz+ey5sWBcA== -----END PRIVATE KEY-----
PKCS#1 私鑰
-----BEGIN RSA PRIVATE KEY----- MIICXQIBAAKBgQC7PyjMEuniN6BPn8oqzIZ6AO1NjSTO9R3adCCIwKfKIEoWXXM+ tHDpktdPKSaAsWJPTNAGvEvtxOfzXib/EMXKqD0eUy5MatfpRjRdf1hJVimmfrb0 9Qx2j7CsKLy7nD23m4xubdYBwvkjMwt/L3JxB5D6qryW1wei/j1c+/OCxQIDAQAB AoGAT7vGYJgRNf4f6qgNS4pKHTu10RcwPFyOOM7IZ9M5380+HyXuBB6MEjowKwpH 1fcy+LepwaR+5KG7b5uBGY4H2ticMtdysBd9gLwnY4Eh4j7LCWE54HvELpeWXkWp FQdb/NQhcqMAGwYsTnRPdBqkrUmJBTYqEGkIlqCQ5vUJOCECQQDhe0KGmbq1RWp6 TDvgpA2dUmlt2fdP8oNW8O7MvbDaQRduoZnVRTPYCDKfzFqpNXL1hAYgth1N0vzD nv3VoLcpAkEA1JcY+rLv5js1g5Luv8LaI5/3uOg0CW7fmh/LfGuz8k/OxASN+cAO UjPHrxtc5xn1zat4/bnV5GEdlOp/DhquPQJBAIV2Fsdi4M+AueiPjPWHRQO0jvDV jfwFOFZSn5YSRUa6NmtmPY6tumUJXSWWqKb1GwlVTuc3xBqXYsNLLUWwLhkCQQDJ UJCiD0LohhdGEqUuSKnj5H9kxddJO4pZXFSI7UEJbJQDwcBkyn+FTm2BH+tZGZdQ fVnlA89OJr0poOpSg+eNAkAKY85SR9KASaTiDBoPpJ8N805XEhd0Kq+ghzSThxL3 fVtKUQLiCh7Yd8oMd/G5S3xWJHUXSioATT8uPRH2bOb/ -----END RSA PRIVATE KEY-----
引用以下 Nuget 包
https://www.nuget.org/packages/System.Extended/
直接使用 RSACryptoServiceProvider，會發現多出幾個擴展方法
參數為密鑰Base64轉碼的字節數組
var private_key = @"MIICdgIBADANBgkqhkiG9w0BAQEFAASCAmAwggJcAgEAAoGBAJGHu8qruvoSFKD3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";
var public_key = @"MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCRh7vKq7r6EhSg9y6iD38Vy08z
umEJXhNTIGe8vRjdpE118Nu1cPRZ0AU9FbMIx8cnQtgCqGgW3DPDLj4VmlmdnJ8P
cFHBBWgh85P1hicv8BQ0nLLjqezaBcS9EmO1C7zhdONVrvMFyHc1j76e+Fv+XfC6
CRvwKfqX+j5OMmWtowIDAQAB";
var rsa = new RSACryptoServiceProvider();
rsa.FromX509PublicKey(Convert.FromBase64String(public_key));
var bytes = rsa.Encrypt(Encoding.UTF8.GetBytes("mangohappy"), false);
rsa.FromPKCS8PrivateKey(Convert.FromBase64String(private_key));
Console.WriteLine(Encoding.UTF8.GetString(rsa.Decrypt(bytes, false)));
注意：.NET的 RSACryptoServiceProvider 只支持公鑰加密，私鑰解密，以上還有加密的 PKCS#8 格式的私鑰，我就沒有處理了，PKCS#1和PKCS#8的公鑰都是X509格式
