RandomNumberGenerator C#

What is the RandomNumberGenerator Class

Before diving into IronPDF integration, let's briefly revisit what makes RandomNumberGenerator special.

• It is part of the System.Security.Cryptography namespace.

• It generates cryptographically strong random values as random byte, much more secure than the typical Random class.

• It's ideal for scenarios requiring unpredictability, such as generating secure tokens, keys, salts, and unique identifiers.

• Uses Cryptographic algorithms like AES-CTR DRBG, Fortuna, or OS-provided CSPRNGs. Making it resistant to prediction.

• Best used for tasks such as creating cryptographic keys, password generation, secure tokens, unique document IDs.

This strength comes from relying on the operating system’s underlying secure random number generators, making it resistant to prediction or reverse-engineering attacks. Unlike pseudo random number generators that may produce the same sequence with the same seed value, this class is designed for true randomness and cryptographic purposes.

Why Use RandomNumberGenerator with IronPDF

IronPDF is a robust .NET PDF library, enabling developers to create, edit, and secure PDF documents. Common use cases where randomness matters includes:

• Unique Document Identifiers: Attach cryptographically secure IDs to PDFs for tracking or validation.

• Secure Watermarks: Embed random watermarks or codes that deter forgery.

• Encryption Keys or Passwords: Generate secure keys or passwords for PDF encryption.

• Random Content: Add random unique tokens or salts to PDF documents for integrity verification.

How to Generate Secure Random Data in C

Here's a simple example of generating a 128-bit (16-byte) secure random token.

using System;
using System.Security.Cryptography;

public static string GenerateSecureToken(int size = 16)
{
    byte[] randomBytes = new byte[size];
    RandomNumberGenerator.Fill(randomBytes);
    return Convert.ToBase64String(randomBytes);
}

using System;
using System.Security.Cryptography;

public static string GenerateSecureToken(int size = 16)
{
    byte[] randomBytes = new byte[size];
    RandomNumberGenerator.Fill(randomBytes);
    return Convert.ToBase64String(randomBytes);
}

This method creates a secure byte array and returns it as a Base64 string — perfect for embedding or tracking in unit tests, filenames, or secure IDs.

Practical Example: Adding Unique Document IDs to PDF Documents

Let's combine the power of RandomNumberGenerator and IronPDF to generate a PDF with a unique, secure document ID stamped on each page.

string GenerateDocumentId()
{
    byte[] idBytes = new byte[12]; // 96-bit ID
    RandomNumberGenerator.Fill(idBytes);
    return BitConverter.ToString(idBytes).Replace("-", "");
}

string GenerateDocumentId()
{
    byte[] idBytes = new byte[12]; // 96-bit ID
    RandomNumberGenerator.Fill(idBytes);
    return BitConverter.ToString(idBytes).Replace("-", "");
}

using IronPdf;

void CreatePdfWithSecureId()
{
    var documentId = GenerateDocumentId();

    var renderer = new ChromePdfRenderer();

    // Add a custom footer with the document ID
    renderer.RenderingOptions.HtmlFooter = new HtmlHeaderFooter
    {
        HtmlFragment = $"<div style='text-align: center; font-size: 10px;'>Document ID: {documentId} - Generated on {DateTime.UtcNow:yyyy-MM-dd HH:mm:ss} UTC</div>",
        DrawDividerLine = true,
    };
    var pdf = renderer.RenderHtmlAsPdf($"<h1>Secure Document</h1><p>Document ID: {documentId}</p>");

    string outputPath = $"SecurePdf_{documentId}.pdf";
    pdf.SaveAs(outputPath);

    Console.WriteLine($"PDF saved as {outputPath}");
}What this Code Does:

using IronPdf;

void CreatePdfWithSecureId()
{
    var documentId = GenerateDocumentId();

    var renderer = new ChromePdfRenderer();

    // Add a custom footer with the document ID
    renderer.RenderingOptions.HtmlFooter = new HtmlHeaderFooter
    {
        HtmlFragment = $"<div style='text-align: center; font-size: 10px;'>Document ID: {documentId} - Generated on {DateTime.UtcNow:yyyy-MM-dd HH:mm:ss} UTC</div>",
        DrawDividerLine = true,
    };
    var pdf = renderer.RenderHtmlAsPdf($"<h1>Secure Document</h1><p>Document ID: {documentId}</p>");

    string outputPath = $"SecurePdf_{documentId}.pdf";
    pdf.SaveAs(outputPath);

    Console.WriteLine($"PDF saved as {outputPath}");
}What this Code Does:

using IronPdf;
using IronPdf.Editing;
using System;
using System.Security.Cryptography;

class Program
{
    public static void Main(string[] args)
    {
        // Create an instance of Program to run non-static methods
        var program = new Program();
        program.CreatePdfWithSecureId()
    }

    string GenerateDocumentId()
    {
        byte[] idBytes = new byte[12]; // 96-bit ID
        RandomNumberGenerator.Fill(idBytes);
        return BitConverter.ToString(idBytes).Replace("-", "");
    }

    void CreatePdfWithSecureId()
    {
        var documentId = GenerateDocumentId();

        var renderer = new ChromePdfRenderer();
        // Add a custom footer with the document ID
        renderer.RenderingOptions.HtmlFooter = new HtmlHeaderFooter
        {
            HtmlFragment = $"<div style='text-align: center; font-size: 10px;'>Document ID: {documentId} - Generated on {DateTime.UtcNow:yyyy-MM-dd HH:mm:ss} UTC</div>",
            DrawDividerLine = true,
        };
        var pdf = renderer.RenderHtmlAsPdf($"<h1>Secure Document</h1><p>Document ID: {documentId}</p>");

        string outputPath = $"SecurePdf_{documentId}.pdf";
        pdf.SaveAs(outputPath);

        Console.WriteLine($"PDF saved as {outputPath}");
    }
}

using IronPdf;
using IronPdf.Editing;
using System;
using System.Security.Cryptography;

class Program
{
    public static void Main(string[] args)
    {
        // Create an instance of Program to run non-static methods
        var program = new Program();
        program.CreatePdfWithSecureId()
    }

    string GenerateDocumentId()
    {
        byte[] idBytes = new byte[12]; // 96-bit ID
        RandomNumberGenerator.Fill(idBytes);
        return BitConverter.ToString(idBytes).Replace("-", "");
    }

    void CreatePdfWithSecureId()
    {
        var documentId = GenerateDocumentId();

        var renderer = new ChromePdfRenderer();
        // Add a custom footer with the document ID
        renderer.RenderingOptions.HtmlFooter = new HtmlHeaderFooter
        {
            HtmlFragment = $"<div style='text-align: center; font-size: 10px;'>Document ID: {documentId} - Generated on {DateTime.UtcNow:yyyy-MM-dd HH:mm:ss} UTC</div>",
            DrawDividerLine = true,
        };
        var pdf = renderer.RenderHtmlAsPdf($"<h1>Secure Document</h1><p>Document ID: {documentId}</p>");

        string outputPath = $"SecurePdf_{documentId}.pdf";
        pdf.SaveAs(outputPath);

        Console.WriteLine($"PDF saved as {outputPath}");
    }
}

Advanced Use Case: Secure PDF Encryption with Random Keys

IronPDF supports PDF encryption, providing strong support for secure PDF creation. You can use RandomNumberGenerator to create strong passwords or keys for encryption:

using IronPdf;
using IronPdf.Editing;
using System;
using System.Security.Cryptography;

class Program
{
    public static void Main(string[] args)
    {
        // Create an instance of Program to run non-static methods
        var program = new Program();
        program.CreateEncryptedPdf();
    }

    string GenerateSecurePassword(int length = 12)
    {
        const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!@#$%^&*()";
        byte[] data = new byte[length];
        RandomNumberGenerator.Fill(data);

        char[] result = new char[length];
        for (int i = 0; i < length; i++)
        {
            result[i] = chars[data[i] % chars.Length];
        }
        return new string(result);
    }

    void CreateEncryptedPdf()
    {
        string password = GenerateSecurePassword();

        var renderer = new ChromePdfRenderer();
        var pdf = renderer.RenderHtmlAsPdf("<h1>Confidential PDF</h1><p>Access is restricted.</p>");

        // Set security settings
        pdf.SecuritySettings.UserPassword = password;
        pdf.SecuritySettings.AllowUserAnnotations = false;
        pdf.SecuritySettings.AllowUserCopyPasteContent = false;
        pdf.SecuritySettings.AllowUserPrinting = IronPdf.Security.PdfPrintSecurity.NoPrint;

        string filePath = "EncryptedSecurePdf.pdf";
        pdf.SaveAs(filePath);

        Console.WriteLine($"Encrypted PDF saved to {filePath} with password: {password}");
    }
}

using IronPdf;
using IronPdf.Editing;
using System;
using System.Security.Cryptography;

class Program
{
    public static void Main(string[] args)
    {
        // Create an instance of Program to run non-static methods
        var program = new Program();
        program.CreateEncryptedPdf();
    }

    string GenerateSecurePassword(int length = 12)
    {
        const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!@#$%^&*()";
        byte[] data = new byte[length];
        RandomNumberGenerator.Fill(data);

        char[] result = new char[length];
        for (int i = 0; i < length; i++)
        {
            result[i] = chars[data[i] % chars.Length];
        }
        return new string(result);
    }

    void CreateEncryptedPdf()
    {
        string password = GenerateSecurePassword();

        var renderer = new ChromePdfRenderer();
        var pdf = renderer.RenderHtmlAsPdf("<h1>Confidential PDF</h1><p>Access is restricted.</p>");

        // Set security settings
        pdf.SecuritySettings.UserPassword = password;
        pdf.SecuritySettings.AllowUserAnnotations = false;
        pdf.SecuritySettings.AllowUserCopyPasteContent = false;
        pdf.SecuritySettings.AllowUserPrinting = IronPdf.Security.PdfPrintSecurity.NoPrint;

        string filePath = "EncryptedSecurePdf.pdf";
        pdf.SaveAs(filePath);

        Console.WriteLine($"Encrypted PDF saved to {filePath} with password: {password}");
    }
}

This method uses default implementation from the OS’s RNG, producing a password suitable for cryptographic operations.

This will apply the generated secure password, so only users with access to the passwords will be able to view the document.

Additionally, we will be left with a encrypted, secure document with our set permissions:

Best Practices and Tips

• Always use RandomNumberGenerator for anything security-related. Avoid Random for IDs, tokens, or passwords.

• Keep sensitive data out of logs or user-facing messages, but log enough to track and audit.

• Consider using timestamps and other metadata alongside random IDs for better traceability.

• Use IronPDF's built-in security features combined with random keys to protect your documents.

• Validate random data length and encoding to ensure usability in your context (e.g., filenames, URLs, barcodes).

Summary

Integrating C#'s RandomNumberGenerator class with IronPDF empowers you to generate secure, unique PDFs that meet modern security standards. Whether you're stamping unique ID's, generating encryption keys, or embedding secure tokens, this approach helps you:

• Prevent document forgery

• Improve traceability

• Secure sensitive data within your PDFs

By combining the cryptographic strength of this class with IronPDF's versatile PDF tools, your PDF solutions become safer and more professional.