可用的 .net core 支持 RSA 私钥加密工具类

首先说明 MS并不建议私钥加密，而且.net 于安全的考虑，RSACryptoServiceProvider类解密时只有同时拥有公钥和私钥才可以，原因是公钥是公开的，会被多人持有，这样的数据传输是不安全的。但是架不住有BouncyCastle这个第三方组件，也是可以实现的。只不过在.net core 2.2 下，没有了 RSACryptoServiceProvider，只好改用 System.Security.Cryptography.RSA 来实现 RSA 私钥加密

 #Const SUPPORT_PRIVATE_ENCRYPT = True
 Imports System.IO
 Imports System.Text
 Imports System.Security.Cryptography

 #If SUPPORT_PRIVATE_ENCRYPT Then
 Imports Org.BouncyCastle.Math
 Imports Org.BouncyCastle.Crypto
 Imports Org.BouncyCastle.Security
 Imports Org.BouncyCastle.Crypto.Parameters
 #End If

 ''' <summary>
 ''' RSA 加密解密辅助类
 ''' </summary>
 ''' <remarks></remarks>
 Public Class RSAHelper

     Private Shared _privateKey As String

     ''' <summary>
     ''' RSA私钥,包含公钥和私钥
     ''' </summary>
     ''' <value></value>
     ''' <returns></returns>
     ''' <remarks></remarks>
     Public Shared ReadOnly Property PrivateKey As String
         Get
             Return _privateKey
         End Get
     End Property

     Private Shared _publicKey As String

     ''' <summary>
     ''' RSA公钥,只包含公钥
     ''' </summary>
     ''' <value></value>
     ''' <returns></returns>
     ''' <remarks></remarks>
     Public Shared ReadOnly Property PublicKey As String
         Get
             Return _publicKey
         End Get
     End Property

     ''' <summary>
     ''' 创建RSA密钥对
     ''' </summary>
     ''' <param name="keySize">512,1024 ...</param>
     ''' <returns></returns>
     ''' <remarks></remarks>
     Public Shared Function CreateRSAKey(Optional ByVal keySize As Int32 = ) As Boolean
         _privateKey = Nothing
         _publicKey = Nothing
         Try
             'Dim provider As New RSACryptoServiceProvider(keySize)
             Dim provider = RSA.Create()
             provider.KeySize = keySize
             _privateKey = provider.ToXml(True)
             _publicKey = provider.ToXml(False)

             Console.WriteLine("max encrypt buffer size:{0}", (keySize / ) - )
             Console.WriteLine("max decrypt buffer size:{0}", keySize / )

             Console.WriteLine(provider.ToPem(True))
             Console.WriteLine()
             Console.WriteLine(provider.ToPem(False))

             Console.WriteLine(provider.ToXml(True))
             Console.WriteLine()
             Console.WriteLine(provider.ToXml(False))

 #If SUPPORT_PRIVATE_ENCRYPT Then
             '验证秘钥对
             provider.FromXml(_privateKey)
             Dim p = provider.ExportParameters(True)
             Dim rkpPrivate As New RsaKeyParameters(True, New BigInteger(, p.Modulus), New BigInteger(p.D))
             Dim rkpPublic As New RsaKeyParameters(False, New BigInteger(, p.Modulus), New BigInteger(p.Exponent))
             '密钥对有无效的概率，不报错的才可用
 #End If
             Return True
         Catch ex As Exception
             Debug.Print("CreateRSAKey({0}) failed, err:{1}", keySize, ex.Message)
             Return False
         End Try
     End Function

     Private Shared Function isKeyValid(ByVal key As String) As Boolean
         If String.IsNullOrEmpty(key) Then
             Return False
         End If
         If key.Trim().Length =  Then
             Return False
         End If

         Return True
     End Function

     ''' <summary>
     ''' 公钥加密
     ''' </summary>
     ''' <param name="publicKey" >公钥(XML格式字符串)</param>
     ''' <param name="plaintext">待加密字符串，明文</param>
     ''' <returns></returns>
     Public Shared Function PublicKeyEncrypt(ByVal publicKey As String, plaintext As String) As String
         '默认只能使用[公钥]进行加密(想使用[公钥解密]可使用第三方组件BouncyCastle来实现)
         If String.IsNullOrEmpty(plaintext) Then
             Return String.Empty
         End If

         If Not isKeyValid(publicKey) Then
             Throw New ArgumentException("Invalid Public Key")
         End If

         '创建RSA对象并载入[公钥]
         Dim provider = RSA.Create
         provider.FromXml(publicKey)

         If (provider.KeySize /  - ) <= plaintext.Length Then
             Throw New ArgumentException("plaintext is too long, try PublicKeyEncryptEx please")
         End If

         '对数据进行加密
         Dim publicValue() As Byte = provider.Encrypt(Encoding.UTF8.GetBytes(plaintext), RSAEncryptionPadding.Pkcs1)
         Dim ciphertext As String = Convert.ToBase64String(publicValue) '使用Base64将byte转换为string
         Return ciphertext
     End Function

     ''' <summary>
     ''' 私钥解密
     ''' </summary>
     ''' <param name="privateKey" >私钥(XML格式字符串)</param>
     ''' <param name="ciphertext">待解密字符串，密文</param>
     ''' <returns></returns>
     Public Shared Function PrivateKeyDecrypt(ByVal privateKey As String, ByVal ciphertext As String) As String
         '默认只能使用[私钥]进行解密(想使用[私钥加密]可使用第三方组件BouncyCastle来实现)
         If String.IsNullOrEmpty(ciphertext) Then
             Return String.Empty
         End If

         If Not isKeyValid(privateKey) Then
             Throw New ArgumentException("Invalid Private Key")
         End If

         '创建RSA对象并载入[私钥]
         Dim provider = RSA.Create
         provider.FromXml(privateKey)

         If (provider.KeySize /  / ) <= ciphertext.Length /  Then
             Throw New ArgumentException("ciphertext is too long, try PrivateKeyDecryptEx please")
         End If

         '对数据进行解密
         Dim privateValue() As Byte = provider.Decrypt(Convert.FromBase64String(ciphertext), RSAEncryptionPadding.Pkcs1) '使用Base64将string转换为byte
         Dim plaintext As String = Encoding.UTF8.GetString(privateValue)
         Return plaintext
     End Function

     ''' <summary>
     ''' 公钥加密
     ''' </summary>
     ''' <param name="publicKey">公钥(XML格式字符串)</param>
     ''' <param name="plaintext">待加密字符串，明文,长度不限</param>
     ''' <returns></returns>
     ''' <remarks></remarks>
     Public Shared Function PublicKeyEncryptEx(ByVal publicKey As String, ByVal plaintext As String) As String
         If String.IsNullOrEmpty(plaintext) Then
             Return String.Empty
         End If

         If Not isKeyValid(publicKey) Then
             Throw New ArgumentException("Invalid Public Key")
         End If

         '载入公钥
         Dim provider = RSA.Create
         provider.FromXml(publicKey)

         Dim inputBytes = Encoding.UTF8.GetBytes(plaintext) '有含义的字符串转化为字节流
         Dim bufferSize As Integer = (provider.KeySize / ) -  '单块最大长度
         Dim buffer = New Byte(bufferSize - ) {}
         Using inputStream As New MemoryStream(inputBytes), outputStream As New MemoryStream()
             Do
                 Dim readSize As Integer = inputStream.Read(buffer, , bufferSize)
                 If readSize <=  Then
                     Exit Do
                 End If

                 Dim temp = New Byte(readSize - ) {}
                 Array.Copy(buffer, , temp, , readSize)
                 Dim encryptedBytes = provider.Encrypt(temp, RSAEncryptionPadding.Pkcs1) 'False)
                 outputStream.Write(encryptedBytes, , encryptedBytes.Length)
             Loop
             Return Convert.ToBase64String(outputStream.ToArray()) '转化为字节流方便传输
         End Using

     End Function

     ''' <summary>
     ''' 私钥解密
     ''' </summary>
     ''' <param name="privateKey">私钥(XML格式字符串)</param>
     ''' <param name="ciphertext">待解密字符串，密文,长度不限</param>
     ''' <returns></returns>
     ''' <remarks></remarks>
     Public Shared Function PrivateKeyDecryptEx(ByVal privateKey As String, ByVal ciphertext As String) As String
         If String.IsNullOrEmpty(ciphertext) Then
             Return String.Empty
         End If

         If Not isKeyValid(privateKey) Then
             Throw New ArgumentException("Invalid Private Key")
         End If

         '载入私钥
         Dim provider = RSA.Create
         provider.FromXml(privateKey)

         Dim inputBytes = Convert.FromBase64String(ciphertext)
         Dim bufferSize As Integer = provider.KeySize /
         Dim buffer = New Byte(bufferSize - ) {}
         Using inputStream As New MemoryStream(inputBytes), outputStream As New MemoryStream()
             Do
                 Dim readSize As Integer = inputStream.Read(buffer, , bufferSize)
                 If readSize <=  Then
                     Exit Do
                 End If

                 Dim temp = New Byte(readSize - ) {}
                 Array.Copy(buffer, , temp, , readSize)
                 Dim rawBytes = provider.Decrypt(temp, RSAEncryptionPadding.Pkcs1)
                 outputStream.Write(rawBytes, , rawBytes.Length)
             Loop
             Return Encoding.UTF8.GetString(outputStream.ToArray())
         End Using
     End Function

 #Region "   依赖 BouncyCastle 实现私钥加密，公钥解密"
 #If SUPPORT_PRIVATE_ENCRYPT Then

     ''' <summary>
     ''' 私钥加密
     ''' </summary>
     ''' <param name="privateKey"> 私钥(XML格式字符串)</param>
     ''' <param name="plaintext"> 要加密的数据 </param>
     ''' <returns> 加密后的数据 </returns>
     Public Shared Function PrivateKeyEncrypt(ByVal privateKey As String, ByVal plaintext As String) As String
         If String.IsNullOrEmpty(plaintext) Then
             Return String.Empty
         End If

         If Not isKeyValid(privateKey) Then
             Throw New ArgumentException("Invalid Private Key")
         End If

         '加载私钥
         Dim provider = RSA.Create
         provider.FromXml(privateKey)
         Dim keyPair = DotNetCoreUtilities.GetKeyPair(provider)

         Dim c As IBufferedCipher = CipherUtilities.GetCipher("RSA/ECB/PKCS1Padding") '使用RSA/ECB/PKCS1Padding格式
         '第一个参数为true表示加密，为false表示解密；第二个参数表示密钥
         c.Init(True, keyPair.Private)

         Dim DataToEncrypt() As Byte = Encoding.UTF8.GetBytes(plaintext)
         Dim outBytes() As Byte = c.DoFinal(DataToEncrypt) '加密
         Dim strBase64 As String = Convert.ToBase64String(outBytes)

         Return strBase64

     End Function

     ''' <summary>
     ''' 私钥加密
     ''' </summary>
     ''' <param name="privateKey"> 私钥(XML格式字符串)</param>
     ''' <param name="plaintext"> 要加密的数据,长度不限 </param>
     ''' <returns> 加密后的数据 </returns>
     Public Shared Function PrivateKeyEncryptEx(ByVal privateKey As String, ByVal plaintext As String) As String
         If String.IsNullOrEmpty(plaintext) Then
             Return String.Empty
         End If

         If Not isKeyValid(privateKey) Then
             Throw New ArgumentException("Invalid Private Key")
         End If

         '加载私钥
         Dim provider = RSA.Create 'As New RSACryptoServiceProvider()
         provider.FromXml(privateKey)
         Dim keyPair = DotNetCoreUtilities.GetKeyPair(provider)

         Dim c As IBufferedCipher = CipherUtilities.GetCipher("RSA/ECB/PKCS1Padding") '使用RSA/ECB/PKCS1Padding格式
         ''第一个参数为true表示加密，为false表示解密；第二个参数表示密钥
         c.Init(True, keyPair.Private) ' keyPair.Private)

         Dim inputBytes = Encoding.UTF8.GetBytes(plaintext)
         Dim bufferSize As Integer = provider.KeySize /  -
         Dim buffer = New Byte(bufferSize - ) {}
         Dim outputStream As New MemoryStream()
         Using inputStream As New MemoryStream(inputBytes)
             Do
                 Dim readSize As Integer = inputStream.Read(buffer, , bufferSize)
                 If readSize <=  Then
                     Exit Do
                 End If

                 Dim temp = New Byte(readSize - ) {}
                 Array.Copy(buffer, , temp, , readSize)
                 Dim rawBytes = c.DoFinal(temp)
                 outputStream.Write(rawBytes, , rawBytes.Length)
             Loop
         End Using
         Return Convert.ToBase64String(outputStream.ToArray())
     End Function

     ''' <summary>
     ''' 公钥解密
     ''' </summary>
     ''' <param name="publicKey"> 公钥(XML格式字符串) </param>
     ''' <param name="ciphertext"> 要解密数据 </param>
     ''' <returns> 解密后的数据 </returns>
     Public Shared Function PublicKeyDecrypt(ByVal publicKey As String, ByVal ciphertext As String) As String
         If String.IsNullOrEmpty(ciphertext) Then
             Return String.Empty
         End If

         If Not isKeyValid(publicKey) Then
             Throw New ArgumentException("Invalid Public Key")
         End If

         '加载公钥
         Dim provider = RSA.Create
         provider.FromXml(publicKey)
         Dim keyParameter = DotNetCoreUtilities.GetKeyParmeter(provider.ToPem(False))

         Dim c As IBufferedCipher = CipherUtilities.GetCipher("RSA/ECB/PKCS1Padding")
         '第一个参数为true表示加密，为false表示解密；第二个参数表示密钥
         c.Init(False, keyParameter)

         Dim DataToDecrypt() As Byte = Convert.FromBase64String(ciphertext)
         Dim outBytes() As Byte = c.DoFinal(DataToDecrypt) '解密

         Dim strDec As String = Encoding.UTF8.GetString(outBytes)
         Return strDec
     End Function

     ''' <summary>
     ''' 公钥解密
     ''' </summary>
     ''' <param name="publicKey"> 公钥(XML格式字符串) </param>
     ''' <param name="ciphertext"> 要解密数据,长度不限 </param>
     ''' <returns> 解密后的数据 </returns>
     Public Shared Function PublicKeyDecryptEx(ByVal publicKey As String, ByVal ciphertext As String) As String
         If String.IsNullOrEmpty(ciphertext) Then
             Return String.Empty
         End If

         If Not isKeyValid(publicKey) Then
             Throw New ArgumentException("Invalid Public Key")
         End If

         '加载公钥
         Dim provider = RSA.Create
         provider.FromXml(publicKey)
         Dim keyParameter = DotNetCoreUtilities.GetKeyParmeter(provider.ToPem(False))

         Dim c As IBufferedCipher = CipherUtilities.GetCipher("RSA/ECB/PKCS1Padding")
         '第一个参数为true表示加密，为false表示解密；第二个参数表示密钥
         c.Init(False, keyParameter)

         Dim inputBytes = Convert.FromBase64String(ciphertext)
         Dim bufferSize As Integer = provider.KeySize /
         Dim buffer = New Byte(bufferSize - ) {}
         Dim outputStream As New MemoryStream()
         Using inputStream As New MemoryStream(inputBytes)
             Do
                 Dim readSize As Integer = inputStream.Read(buffer, , bufferSize)
                 If readSize <=  Then
                     Exit Do
                 End If

                 Dim temp = New Byte(readSize - ) {}
                 Array.Copy(buffer, , temp, , readSize)
                 Dim rawBytes = c.DoFinal(temp)
                 outputStream.Write(rawBytes, , rawBytes.Length)
             Loop
         End Using
         Return Encoding.UTF8.GetString(outputStream.ToArray())
     End Function
 #End If
 #End Region
 End Class

扩展方法

 Imports System.Security.Cryptography
 Imports System.Xml
 Imports Org.BouncyCastle.Crypto.Parameters
 Imports Org.BouncyCastle.Crypto
 Imports Org.BouncyCastle.Math
 Imports System.IO
 Imports Org.BouncyCastle.OpenSsl
 Imports Org.BouncyCastle.Security
 Imports System.Text

 Friend Module RsaExtention

     <System.Runtime.CompilerServices.Extension>
     Public Sub FromXml(ByVal rsa As RSA, ByVal xmlString As String)
         Dim parameters As New RSAParameters()
         Dim xmlDoc As New XmlDocument()
         xmlDoc.LoadXml(xmlString)
         If xmlDoc.DocumentElement.Name.Equals("RSAKeyValue") Then
             For Each node As XmlNode In xmlDoc.DocumentElement.ChildNodes
                 Select Case node.Name
                     Case "Modulus"
                         parameters.Modulus = Convert.FromBase64String(node.InnerText)
                     Case "Exponent"
                         parameters.Exponent = Convert.FromBase64String(node.InnerText)
                     Case "P"
                         parameters.P = Convert.FromBase64String(node.InnerText)
                     Case "Q"
                         parameters.Q = Convert.FromBase64String(node.InnerText)
                     Case "DP"
                         parameters.DP = Convert.FromBase64String(node.InnerText)
                     Case "DQ"
                         parameters.DQ = Convert.FromBase64String(node.InnerText)
                     Case "InverseQ"
                         parameters.InverseQ = Convert.FromBase64String(node.InnerText)
                     Case "D"
                         parameters.D = Convert.FromBase64String(node.InnerText)
                 End Select
             Next node
         Else
             Throw New Exception("Invalid XML RSA key.")
         End If

         rsa.ImportParameters(parameters)
     End Sub

     <System.Runtime.CompilerServices.Extension>
     Public Function ToXml(ByVal rsa As RSA, ByVal includePrivateParameters As Boolean) As String
         Dim parameters As RSAParameters = rsa.ExportParameters(includePrivateParameters)

         Dim ret As String
         If includePrivateParameters Then
             ret = String.Format("<RSAKeyValue><Modulus>{0}</Modulus><Exponent>{1}</Exponent><P>{2}</P><Q>{3}</Q><DP>{4}</DP><DQ>{5}</DQ><InverseQ>{6}</InverseQ><D>{7}</D></RSAKeyValue>",
                                  Convert.ToBase64String(parameters.Modulus),
                                  Convert.ToBase64String(parameters.Exponent),
                                  Convert.ToBase64String(parameters.P),
                                  Convert.ToBase64String(parameters.Q),
                                  Convert.ToBase64String(parameters.DP),
                                  Convert.ToBase64String(parameters.DQ),
                                  Convert.ToBase64String(parameters.InverseQ),
                                  Convert.ToBase64String(parameters.D))
         Else
             ret = String.Format("<RSAKeyValue><Modulus>{0}</Modulus><Exponent>{1}</Exponent></RSAKeyValue>",
                                 Convert.ToBase64String(parameters.Modulus),
                                 Convert.ToBase64String(parameters.Exponent))
         End If
         Return formatXml(ret)
     End Function

     Private Function formatXml(ByVal sUnformattedXml As String) As String
         Dim xd As New XmlDocument()
         xd.LoadXml(sUnformattedXml)
         Dim sb As New StringBuilder()
         Dim sw As New StringWriter(sb)
         Dim xtw As XmlTextWriter = Nothing
         Try
             xtw = New XmlTextWriter(sw)
             xtw.Formatting = Formatting.Indented
             xtw.Indentation =
             xtw.IndentChar = Char.Parse(vbTab)
             xd.WriteTo(xtw)
         Finally
             If xtw IsNot Nothing Then
                 xtw.Close()
             End If
         End Try
         Return sb.ToString()
     End Function

     <System.Runtime.CompilerServices.Extension>
     Public Sub FromPem(ByVal rsa As RSA, pemString As String)
         Const FLAG_PUBLIC As String = "-----BEGIN PUBLIC KEY-----"
         Const FLAG_PRIVATE As String = "-----BEGIN PRIVATE KEY-----"

         Dim content As String = pemString

         If pemString.StartsWith(FLAG_PUBLIC) Then
             content = content.Replace(FLAG_PUBLIC, "").Replace("-----END PUBLIC KEY-----", "").Replace(vbCrLf, "")
             Dim publicKeyParam As RsaKeyParameters = PublicKeyFactory.CreateKey(Convert.FromBase64String(content))
             Dim xml As String = String.Format("<RSAKeyValue><Modulus>{0}</Modulus><Exponent>{1}</Exponent></RSAKeyValue>",
                                               Convert.ToBase64String(publicKeyParam.Modulus.ToByteArrayUnsigned),
                                               Convert.ToBase64String(publicKeyParam.Exponent.ToByteArrayUnsigned))
             rsa.FromXml(xml)
         ElseIf pemString.StartsWith(FLAG_PRIVATE) Then
             content = content.Replace(FLAG_PRIVATE, "").Replace("-----END PRIVATE KEY-----", "").Replace(vbCrLf, "")
             Dim privateKeyParam As RsaPrivateCrtKeyParameters = PrivateKeyFactory.CreateKey(Convert.FromBase64String(content))
             Dim parameters As New RSAParameters() With
                 {
                     .Modulus = privateKeyParam.Modulus.ToByteArrayUnsigned(),
                     .Exponent = privateKeyParam.PublicExponent.ToByteArrayUnsigned(),
                     .P = privateKeyParam.P.ToByteArrayUnsigned(),
                     .Q = privateKeyParam.Q.ToByteArrayUnsigned(),
                     .DP = privateKeyParam.DP.ToByteArrayUnsigned(),
                     .DQ = privateKeyParam.DQ.ToByteArrayUnsigned(),
                     .InverseQ = privateKeyParam.QInv.ToByteArrayUnsigned(),
                     .D = privateKeyParam.Exponent.ToByteArrayUnsigned()
                 }
             rsa.ImportParameters(parameters)
         Else
             Throw New ArgumentException("pemString is not validate")
         End If
     End Sub

     <System.Runtime.CompilerServices.Extension>
     Public Function ToPem(ByVal rsa As RSA, ByVal includePrivateParameters As Boolean) As String
         Dim ret As String = String.Empty
         If includePrivateParameters Then
             Return exportPrivateKey(rsa)
         Else
             Return exportPublicKey(rsa)
         End If
     End Function

     ''' <summary>
     ''' 输出PEM格式公钥
     ''' </summary>
     ''' <param name="rsa"></param>
     ''' <returns></returns>
     Private Function exportPublicKey(ByVal rsa As RSA) As String
         Dim outputStream As TextWriter = New StringWriter()

         Dim parameters = rsa.ExportParameters(False)
         Using stream = New MemoryStream()
             Dim writer = New BinaryWriter(stream)
             writer.Write(CByte(&H30)) ' SEQUENCE
             Using innerStream = New MemoryStream()
                 Dim innerWriter = New BinaryWriter(innerStream)
                 innerWriter.Write(CByte(&H30)) ' SEQUENCE
                 encodeLength(innerWriter, )
                 innerWriter.Write(CByte(&H6)) ' OBJECT IDENTIFIER
                 Dim rsaEncryptionOid = New Byte() {&H2A, &H86, &H48, &H86, &HF7, &HD, &H1, &H1, &H1}
                 encodeLength(innerWriter, rsaEncryptionOid.Length)
                 innerWriter.Write(rsaEncryptionOid)
                 innerWriter.Write(CByte(&H5)) ' NULL
                 encodeLength(innerWriter, )
                 innerWriter.Write(CByte(&H3)) ' BIT STRING
                 Using bitStringStream = New MemoryStream()
                     Dim bitStringWriter = New BinaryWriter(bitStringStream)
                     bitStringWriter.Write(CByte(&H0)) ' # of unused bits
                     bitStringWriter.Write(CByte(&H30)) ' SEQUENCE
                     Using paramsStream = New MemoryStream()
                         Dim paramsWriter = New BinaryWriter(paramsStream)
                         encodeIntegerBigEndian(paramsWriter, parameters.Modulus) ' Modulus
                         encodeIntegerBigEndian(paramsWriter, parameters.Exponent) ' Exponent
                         Dim paramsLength = CInt(paramsStream.Length)
                         encodeLength(bitStringWriter, paramsLength)
                         bitStringWriter.Write(paramsStream.GetBuffer(), , paramsLength)
                     End Using
                     Dim bitStringLength = CInt(bitStringStream.Length)
                     encodeLength(innerWriter, bitStringLength)
                     innerWriter.Write(bitStringStream.GetBuffer(), , bitStringLength)
                 End Using
                 Dim length = CInt(innerStream.Length)
                 encodeLength(writer, length)
                 writer.Write(innerStream.GetBuffer(), , length)
             End Using

             Dim base64 = Convert.ToBase64String(stream.GetBuffer(), , CInt(stream.Length)).ToCharArray()
             outputStream.WriteLine("-----BEGIN PUBLIC KEY-----")
             For i =  To base64.Length -  Step
                 outputStream.WriteLine(base64, i, Math.Min(, base64.Length - i))
             Next i
             outputStream.WriteLine("-----END PUBLIC KEY-----")
         End Using

         Return outputStream.ToString
     End Function

     ''' <summary>
     ''' 输出PEM格式私钥
     ''' </summary>
     ''' <param name="rsa"></param>
     Private Function exportPrivateKey(ByVal rsa As RSA) As String
         'If csp.PublicOnly Then
         '    Throw New ArgumentException("CSP does not contain a private key", "csp")
         'End If

         Dim outputStream As TextWriter = New StringWriter()
         Dim parameters = rsa.ExportParameters(True)
         If parameters.D Is Nothing Then
             Throw New ArgumentException("object does not contain a private key", "csp")
         End If
         Using stream = New MemoryStream()
             Dim writer = New BinaryWriter(stream)
             writer.Write(CByte(&H30)) ' SEQUENCE
             Using innerStream = New MemoryStream()
                 Dim innerWriter = New BinaryWriter(innerStream)
                 encodeIntegerBigEndian(innerWriter, New Byte() {&H0}) ' Version
                 encodeIntegerBigEndian(innerWriter, parameters.Modulus)
                 encodeIntegerBigEndian(innerWriter, parameters.Exponent)
                 encodeIntegerBigEndian(innerWriter, parameters.D)
                 encodeIntegerBigEndian(innerWriter, parameters.P)
                 encodeIntegerBigEndian(innerWriter, parameters.Q)
                 encodeIntegerBigEndian(innerWriter, parameters.DP)
                 encodeIntegerBigEndian(innerWriter, parameters.DQ)
                 encodeIntegerBigEndian(innerWriter, parameters.InverseQ)
                 Dim length = CInt(innerStream.Length)
                 encodeLength(writer, length)
                 writer.Write(innerStream.GetBuffer(), , length)
             End Using

             Dim base64 = Convert.ToBase64String(stream.GetBuffer(), , CInt(stream.Length)).ToCharArray()

             outputStream.WriteLine("-----BEGIN RSA PRIVATE KEY-----")
             ' Output as Base64 with lines chopped at 64 characters
             For i =  To base64.Length -  Step
                 outputStream.WriteLine(base64, i, Math.Min(, base64.Length - i))
             Next i
             outputStream.WriteLine("-----END RSA PRIVATE KEY-----")
         End Using

         Return outputStream.ToString
     End Function

     Private Sub encodeLength(ByVal stream As BinaryWriter, ByVal length As Integer)
         If length <  Then
             Throw New ArgumentOutOfRangeException("length", "Length must be non-negative")
         End If
         If length < &H80 Then
             ' Short form
             stream.Write(CByte(length))
         Else
             ' Long form
             Dim temp = length
             Dim bytesRequired =
             Do While temp >
                 temp >>=
                 bytesRequired +=
             Loop
             stream.Write(CByte(bytesRequired Or &H80))
             For i = bytesRequired -  To  Step -
                 stream.Write(CByte(length >> ( * i) And &HFF))
             Next i
         End If
     End Sub

     Private Sub encodeIntegerBigEndian(ByVal stream As BinaryWriter, ByVal value() As Byte, Optional ByVal forceUnsigned As Boolean = True)
         stream.Write(CByte(&H2)) ' INTEGER
         Dim prefixZeros =
         For i =  To value.Length -
             If value(i) <>  Then
                 Exit For
             End If
             prefixZeros +=
         Next i
         If value.Length - prefixZeros =  Then
             encodeLength(stream, )
             stream.Write(CByte())
         Else
             If forceUnsigned AndAlso value(prefixZeros) > &H7F Then
                 ' Add a prefix zero to force unsigned if the MSB is 1
                 encodeLength(stream, value.Length - prefixZeros + )
                 stream.Write(CByte())
             Else
                 encodeLength(stream, value.Length - prefixZeros)
             End If
             For i = prefixZeros To value.Length -
                 stream.Write(value(i))
             Next i
         End If
     End Sub

 End Module

 Friend Module DotNetCoreUtilities
     ''' <summary>
     ''' 返回 RSA 对象的 密钥对参数对象
     ''' </summary>
     ''' <param name="provider"></param>
     ''' <returns>
     ''' 用私钥初始化的 RSA 对象 - 返回有效的公钥和私钥密钥对
     ''' 用公钥初始化的 RSA 对象 - 返回 有效的公钥 和 无效的私钥组成的密钥对
     ''' </returns>
     Public Function GetKeyPair(ByVal provider As RSA) As AsymmetricCipherKeyPair
         Dim p As RSAParameters
         Dim rkpPrivate As RsaKeyParameters

         Try
             p = provider.ExportParameters(True)
             rkpPrivate = New RsaKeyParameters(True, New BigInteger(, p.Modulus), New BigInteger(p.D)) '//PrivateKey 实际使用
         Catch ex As Exception
             p = provider.ExportParameters(False)
             rkpPrivate = New RsaKeyParameters(True, BigInteger.One, BigInteger.One) '//PrivateKey 实际不使用
         End Try

         Dim rpkPublic As New RsaKeyParameters(False, New BigInteger(, p.Modulus), New BigInteger(p.Exponent))
         Dim keyPair As New AsymmetricCipherKeyPair(rpkPublic, rkpPrivate)
         Return keyPair
     End Function

     ''' <summary>
     ''' 通过 PEM 格式的私钥返回 密钥对参数对象
     ''' </summary>
     ''' <param name="privateKey">PEM 格式的私钥</param>
     ''' <returns></returns>
     Public Function GetKeyPair(ByVal privateKey As String) As AsymmetricCipherKeyPair
         Dim keyPair As AsymmetricCipherKeyPair
         Using StringReader As New StringReader(privateKey)
             Dim pemReader = New PemReader(StringReader)
             keyPair = CType(pemReader.ReadObject, AsymmetricCipherKeyPair)
         End Using
         Return keyPair
     End Function

     ''' <summary>
     ''' 通过 PEM 格式的公钥返回 密钥参数对象
     ''' </summary>
     ''' <param name="publicKey">PEM 格式的公钥</param>
     ''' <returns></returns>
     Public Function GetKeyParmeter(ByVal publicKey As String) As AsymmetricKeyParameter
         Dim ret As AsymmetricKeyParameter
         Using StringReader As New StringReader(publicKey)
             Dim pemReader = New PemReader(StringReader)
             ret = CType(pemReader.ReadObject, AsymmetricKeyParameter)
         End Using
         Return ret
     End Function
 End Module

最后是调用代码示例:

         Dim ciphertext As String = RSAHelper.PublicKeyEncryptEx(RSAHelper.PublicKey, plaintext)
         Console.WriteLine("===== ciphertext.Length={0}, PublicKeyEncypt Result:", ciphertext.Length)
         Console.WriteLine(ciphertext)
         Dim newData As String = RSAHelper.PrivateKeyDecryptEx(RSAHelper.PrivateKey, ciphertext)
         Console.WriteLine("===== PrivateKeyDecrypt Result:")
         Console.WriteLine(newData.Equals(plaintext))
         Console.WriteLine("==============================================")
         Console.WriteLine()
         ciphertext = RSAHelper.PrivateKeyEncryptEx(RSAHelper.PrivateKey, plaintext)
         Console.WriteLine("ciphertext.Length={0}, PrivateKeyEncypt Result:", ciphertext.Length)
         Console.WriteLine(ciphertext)
         newData = RSAHelper.PublicKeyDecryptEx(RSAHelper.PublicKey, ciphertext)
         Console.WriteLine("===== PublicKeyDecrypt {0}", newData.Equals(plaintext))

PS:如果需要与Java交换密钥文件，可参考 https://www.cnblogs.com/wuweimin/p/7839335.html

参考文档：

https://blog.csdn.net/u010792238/article/details/79471406

https://www.cnblogs.com/taiyonghai/p/6150353.html

https://stackoverflow.com/questions/23734792/c-sharp-export-private-public-rsa-key-from-rsacryptoserviceprovider-to-pem-strin/25591659#25591659