'''' This code is part of Document Solutions for PDF .NET demos.'' Copyright (c) MESCIUS inc. All rights reserved.''Imports SystemImports System.IOImports Org.BouncyCastle.Asn1Imports Org.BouncyCastle.CryptoImports Org.BouncyCastle.SecurityImports Org.BouncyCastle.PkcsImports Org.BouncyCastle.Crypto.ParametersImports GrapeCity.Documents.PdfImports GrapeCity.Documents.Pdf.Security
'' This sample shows how to sign an existing PDF file that contains'' an empty signature field with an Elliptic Curve Digital Signature Algorithm'' (ECDSA) certificate.'''' The sample includes a ready to use class BCSignatureGenerator that implements'' the GrapeCity.Documents.Pdf.IPkcs7SignatureGenerator interface using the'' BouncyCastle.Cryptography package. Because unlike the current .NET system libraries,'' BouncyCastle supports ECDSA, the BCSignatureGenerator class can be used in your'' applications to handle ECDSA certificates.Public Class SignWithECDSA    Function CreatePDF(ByVal stream As Stream) As Integer        Dim certPath = Path.Combine("Resources", "Misc", "DsPdfTest3_ECDSA.pfx")        Dim certPwd = "password"
        Dim doc = New GcPdfDocument()        Using s = File.OpenRead(Path.Combine("Resources", "PDFs", "SignWithECDSA.pdf"))            doc.Load(s)
            Dim sp = New SignatureProperties() With {                .SignatureBuilder = New Pkcs7SignatureBuilder() With {                    .SignatureGenerator = New BCSignatureGenerator(certPath, certPwd, OID.HashAlgorithms.SHA256),                    .CertificateChain = SecurityUtils.GetCertificateChain(certPath, certPwd)                },                .SignatureField = doc.AcroForm.Fields(0)            }            sp.SignatureAppearance.Caption = "ECDSA"            doc.Sign(sp, stream)        End Using
        '' Done.        Return doc.Pages.Count    End FunctionEnd Class
''' <summary>''' Implements IPkcs7SignatureGenerator.''' This implementation uses BouncyCastle libraries which,''' unlike the current .NET system libraries, support ECDSA''' (Elliptic Curve Digital Signature Algorithm) keys.''' </summary>Public Class BCSignatureGenerator    Implements IPkcs7SignatureGenerator
    Private _hashAlgorithm As OID    Private _encryptionAlgorithm As OID    Private _encryptionAlgorithmName As String    Private _key As ICipherParameters
    Public Sub New(ByVal key As ICipherParameters, ByVal hashAlgorithm As OID)        _hashAlgorithm = hashAlgorithm        If TypeOf key Is RsaKeyParameters Then            _encryptionAlgorithm = OID.EncryptionAlgorithms.RSA            _encryptionAlgorithmName = "RSA"        ElseIf TypeOf key Is DsaKeyParameters Then            _encryptionAlgorithm = OID.EncryptionAlgorithms.DSA            _encryptionAlgorithmName = "DSA"        ElseIf TypeOf key Is ECKeyParameters Then            _encryptionAlgorithm = OID.EncryptionAlgorithms.ECDSA            _encryptionAlgorithmName = "ECDSA"        Else            Throw New Exception($"Unknown algorithm used in the private key [{key}]")        End If        _key = key    End Sub
    Public Sub New(ByVal certificateData As Byte(), ByVal password As String, ByVal hashAlgorithm As OID)        Me.New(GetPrivateKey(certificateData, password), hashAlgorithm)    End Sub
    Public Sub New(ByVal certificateStream As Stream, ByVal password As String, ByVal hashAlgorithm As OID)        Me.New(GetPrivateKey(certificateStream, password), hashAlgorithm)    End Sub
    Public Sub New(ByVal certificateFileName As String, ByVal password As String, ByVal hashAlgorithm As OID)        Me.New(GetPrivateKey(certificateFileName, password), hashAlgorithm)    End Sub
    Public ReadOnly Property HashAlgorithm As OID Implements IPkcs7SignatureGenerator.HashAlgorithm        Get            Return _hashAlgorithm        End Get    End Property
    Public ReadOnly Property DigestEncryptionAlgorithm As OID Implements IPkcs7SignatureGenerator.DigestEncryptionAlgorithm        Get            Return _encryptionAlgorithm        End Get    End Property
    Public Function SignData(ByVal digest As Byte()) As Byte() Implements IPkcs7SignatureGenerator.SignData        Dim han = DigestUtilities.GetAlgorithmName(New DerObjectIdentifier(_hashAlgorithm.ToString()))        Dim algorithm = han & "with" & _encryptionAlgorithmName        Dim sig As ISigner = SignerUtilities.GetSigner(algorithm)        sig.Init(True, _key)        sig.BlockUpdate(digest, 0, digest.Length)        Return sig.GenerateSignature()    End Function
    Public Shared Function GetPrivateKey(ByVal certificateStream As Stream, ByVal password As String) As ICipherParameters        Dim p = New Char(password.Length - 1) {}        For i = 0 To p.Length - 1            p(i) = password(i)        Next        Dim pk12 As Pkcs12Store = New Pkcs12StoreBuilder().Build()        pk12.Load(certificateStream, p)        For Each a In pk12.Aliases            Dim aliasStr = DirectCast(a, String)            If pk12.IsKeyEntry(aliasStr) Then                Dim keyEntry = pk12.GetKey(aliasStr)                If keyEntry.Key.IsPrivate Then                    Return keyEntry.Key                End If            End If        Next        Throw New Exception("Cannot get private key.")    End Function
    Public Shared Function GetPrivateKey(ByVal certificateFilePath As String, ByVal password As String) As ICipherParameters        Using fs = New FileStream(certificateFilePath, FileMode.Open)            Return GetPrivateKey(fs, password)        End Using    End Function
    Public Shared Function GetPrivateKey(ByVal certificateData As Byte(), ByVal password As String) As ICipherParameters        Using ms = New MemoryStream(certificateData)            Return GetPrivateKey(ms, password)        End Using    End FunctionEnd Class