Text File Signing using PKCS#7 Signature in C#

thanks

Check this:

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

public class FileEncryption
{
    public static void EncryptFile(string inputFile, string outputFile, X509Certificate2 recipientCertificate)
    {
        ContentInfo contentInfo = new ContentInfo(File.ReadAllBytes(inputFile));
        EnvelopedCms envelopedCms = new EnvelopedCms(contentInfo);
        CmsRecipient recipient = new CmsRecipient(recipientCertificate);

        envelopedCms.Encrypt(recipient);

        byte[] encryptedBytes = envelopedCms.Encode();

        File.WriteAllBytes(outputFile, encryptedBytes);
    }

    public static void DecryptFile(string inputFile, string outputFile, X509Certificate2 recipientCertificate)
    {
        byte[] encryptedBytes = File.ReadAllBytes(inputFile);
        EnvelopedCms envelopedCms = new EnvelopedCms();
        envelopedCms.Decode(encryptedBytes);

        envelopedCms.Decrypt(new X509Certificate2Collection(recipientCertificate));

        byte[] decryptedBytes = envelopedCms.ContentInfo.Content;

        File.WriteAllBytes(outputFile, decryptedBytes);
    }
}


// how to use
string inputFile = "path/to/input.txt";
string encryptedFile = "path/to/encrypted.p7";
string decryptedFile = "path/to/decrypted.txt";

// Load the recipient certificate
X509Certificate2 recipientCertificate = new X509Certificate2("path/to/recipient.pfx", "certificatePassword");

FileEncryption1.EncryptFile(inputFile, encryptedFile, recipientCertificate);
FileEncryption1.DecryptFile(encryptedFile, decryptedFile, recipientCertificate);

Console.WriteLine("Encryption and decryption completed successfully!");

Hi Mohamed Azarudeen,

It is showing below error. 

Hi Mohamed Azarudeen,

Please share how to decrypt that encrypted file.

using System;
using System.IO;
using System.Security.Cryptography;
using System.Security.Cryptography.Pkcs;
using System.Security.Cryptography.X509Certificates;
using System.Text;

class Program
{
    static void Main()
    {
        // Step 1: Load the PKCS#12 keystore (pfx file) and get the private key
        string pfxPath = "path/to/your/certificate.pfx";
        string pfxPassword = "your-pfx-password";
        X509Certificate2 certificate = new X509Certificate2(pfxPath, pfxPassword, X509KeyStorageFlags.Exportable);
        RSACryptoServiceProvider privateKey = (RSACryptoServiceProvider)certificate.PrivateKey;

        // Step 2: Specify the signature algorithm
        string signatureAlgorithm = "SHA256";

        // Step 3: Read the original file
        string filePath = "path/to/your/original/file.txt";
        byte[] originalData = File.ReadAllBytes(filePath);

        // Step 4: Create a SignedCms object to generate the PKCS#7 signature
        ContentInfo contentInfo = new ContentInfo(originalData);
        SignedCms signedCms = new SignedCms(contentInfo, true);

        // Step 5: Create a signer with the private key and signature algorithm
        CmsSigner signer = new CmsSigner(privateKey);
        signer.DigestAlgorithm = new Oid(signatureAlgorithm);

        // Step 6: Initiate the signature
        signedCms.ComputeSignature(signer);

        // Step 7: Get the signature bytes
        byte[] signature = signedCms.Encode();

        // Step 8: Convert the signature bytes to Base64
        string base64Signature = Convert.ToBase64String(signature);

        // Step 9: Encode the original file to Base64
        string base64OriginalFile = Convert.ToBase64String(originalData);

        // Step 10: Extract the public key certificate and encode it to Base64
        string base64PublicKeyCertificate = Convert.ToBase64String(certificate.RawData);

        // Now you have the base64Signature, base64OriginalFile, and base64PublicKeyCertificate.
        // You can use them as needed for further processing or verification.

        // Example: Save the signed data to a new file
        string signedFilePath = "path/to/your/signed/file.txt";
        File.WriteAllText(signedFilePath, $"{base64Signature}\n{base64OriginalFile}\n{base64PublicKeyCertificate}");
    }
}

Hi Ashid

 you can use the .NET Framework's cryptography libraries to achieve text file signing using a PKCS#7 signature. Here's the equivalent C# code for the steps involved in signing: