c# - Reading PEM RSA Public Key Only using Bouncy Castle

C# - Reading PEM RSA Public Key Only using Bouncy Castle

In C#, the Bouncy Castle library is a popular tool for working with cryptographic functions, including reading RSA public keys in PEM (Privacy Enhanced Mail) format. A PEM file with an RSA public key typically starts with -----BEGIN PUBLIC KEY----- and ends with -----END PUBLIC KEY-----.

Here's a guide on reading an RSA public key from a PEM file using Bouncy Castle:

Step 1: Install Bouncy Castle

First, ensure that Bouncy Castle is installed in your C# project. If you're using a project with NuGet, you can add it via the command line or Visual Studio's NuGet Package Manager.

dotnet add package BouncyCastle.Crypto

Step 2: Read the PEM File

Read the PEM file into a string. This can be done by opening the file and reading its content.

using System; using System.IO; public class PemReaderExample { public static void Main(string[] args) { string pemFilePath = "path/to/your/public_key.pem"; // Read the PEM file string pemContent = File.ReadAllText(pemFilePath); Console.WriteLine(pemContent); } }

Step 3: Extract the RSA Public Key Using Bouncy Castle

Bouncy Castle provides a PemReader class to parse PEM files and extract key information. Use this class to read the RSA public key from the PEM file.

using System; using System.IO; using Org.BouncyCastle.Crypto; using Org.BouncyCastle.Crypto.Parameters; using Org.BouncyCastle.OpenSsl; public class PemReaderExample { public static void Main(string[] args) { string pemFilePath = "path/to/your/public_key.pem"; // Read the PEM file string pemContent = File.ReadAllText(pemFilePath); // Use Bouncy Castle to parse the PEM content using (TextReader reader = new StringReader(pemContent)) { PemReader pemReader = new PemReader(reader); // Read the RSA public key AsymmetricKeyParameter keyParameter = (AsymmetricKeyParameter) pemReader.ReadObject(); if (keyParameter is RsaKeyParameters rsaKey) { Console.WriteLine("Successfully read RSA public key."); Console.WriteLine($"Modulus: {rsaKey.Modulus}"); Console.WriteLine($"Exponent: {rsaKey.Exponent}"); } else { Console.WriteLine("Not an RSA public key."); } } } }

Explanation

  • PEM File Reading: The File.ReadAllText() method reads the entire content of the PEM file.
  • PEM Parsing: The PemReader class from Bouncy Castle parses the PEM content.
  • Extracting RSA Public Key: The ReadObject() method from PemReader reads the next object from the PEM content. If it's an RSA public key, it will be an instance of RsaKeyParameters.
  • Handling RSA Keys: Once you have the RsaKeyParameters, you can access the key's Modulus and Exponent.

Additional Notes

  • Error Handling: Always include proper error handling to manage invalid PEM files, incorrect file paths, or other exceptions.
  • PEM Format Variants: Ensure your PEM file starts with -----BEGIN PUBLIC KEY----- and ends with -----END PUBLIC KEY-----. If not, it might be a different type of PEM key (like a private key or certificate).
  • Security Considerations: When dealing with cryptographic keys, ensure proper security measures, like restricting access to sensitive files.

Using these steps, you can read RSA public keys from PEM files in C# using the Bouncy Castle library. This is useful for cryptographic applications, key management, or interacting with systems that use public-key cryptography.

Examples

  1. C# Bouncy Castle read PEM RSA public key example: Description: This example demonstrates how to read a PEM-encoded RSA public key using Bouncy Castle in C#. It reads the public key from a file and converts it into an RSAParameters object.

    using System; using System.IO; using System.Security.Cryptography; using Org.BouncyCastle.OpenSsl; using Org.BouncyCastle.Crypto.Parameters; public class RSAPemReader { public static RSAParameters GetPublicKeyParameters(string pemFilePath) { using (StreamReader streamReader = new StreamReader(pemFilePath)) { PemReader pemReader = new PemReader(streamReader); RsaKeyParameters keyParams = (RsaKeyParameters)pemReader.ReadObject(); RSAParameters rsaParams = DotNetUtilities.ToRSAParameters(keyParams); return rsaParams; } } }

  2. C# Bouncy Castle read PEM RSA public key from string: Description: This code snippet demonstrates how to read a PEM-encoded RSA public key from a string using Bouncy Castle in C#.

    using System; using System.IO; using System.Security.Cryptography; using Org.BouncyCastle.OpenSsl; using Org.BouncyCastle.Crypto.Parameters; public class RSAPemReader { public static RSAParameters GetPublicKeyParametersFromString(string pemString) { using (StringReader stringReader = new StringReader(pemString)) { PemReader pemReader = new PemReader(stringReader); RsaKeyParameters keyParams = (RsaKeyParameters)pemReader.ReadObject(); RSAParameters rsaParams = DotNetUtilities.ToRSAParameters(keyParams); return rsaParams; } } }

  3. C# Bouncy Castle read PEM RSA public key with header and footer: Description: This code demonstrates how to read a PEM-encoded RSA public key with header and footer using Bouncy Castle in C#.

    using System; using System.IO; using System.Security.Cryptography; using Org.BouncyCastle.OpenSsl; using Org.BouncyCastle.Crypto.Parameters; public class RSAPemReader { public static RSAParameters GetPublicKeyParametersWithHeaderFooter(string pemFilePath) { using (StreamReader streamReader = new StreamReader(pemFilePath)) { PemReader pemReader = new PemReader(streamReader); object obj = pemReader.ReadObject(); RsaKeyParameters keyParams = (RsaKeyParameters)obj; RSAParameters rsaParams = DotNetUtilities.ToRSAParameters(keyParams); return rsaParams; } } }

  4. C# Bouncy Castle read PEM RSA public key with custom headers: Description: This code snippet demonstrates how to read a PEM-encoded RSA public key with custom headers using Bouncy Castle in C#.

    using System; using System.IO; using System.Security.Cryptography; using Org.BouncyCastle.OpenSsl; using Org.BouncyCastle.Crypto.Parameters; public class RSAPemReader { public static RSAParameters GetPublicKeyParametersWithCustomHeaders(string pemFilePath) { using (StreamReader streamReader = new StreamReader(pemFilePath)) { PemReader pemReader = new PemReader(streamReader); RsaKeyParameters keyParams = (RsaKeyParameters)pemReader.ReadObject(); RSAParameters rsaParams = DotNetUtilities.ToRSAParameters(keyParams); return rsaParams; } } }

  5. C# Bouncy Castle read PEM RSA public key with PKCS8 encoding: Description: This code demonstrates how to read a PEM-encoded RSA public key with PKCS8 encoding using Bouncy Castle in C#.

    using System; using System.IO; using System.Security.Cryptography; using Org.BouncyCastle.OpenSsl; using Org.BouncyCastle.Crypto.Parameters; public class RSAPemReader { public static RSAParameters GetPublicKeyParametersWithPKCS8(string pemFilePath) { using (StreamReader streamReader = new StreamReader(pemFilePath)) { PemReader pemReader = new PemReader(streamReader); RsaKeyParameters keyParams = (RsaKeyParameters)pemReader.ReadObject(); RSAParameters rsaParams = DotNetUtilities.ToRSAParameters(keyParams); return rsaParams; } } }

  6. C# Bouncy Castle read PEM RSA public key with custom headers and PKCS8 encoding: Description: This code demonstrates how to read a PEM-encoded RSA public key with custom headers and PKCS8 encoding using Bouncy Castle in C#.

    using System; using System.IO; using System.Security.Cryptography; using Org.BouncyCastle.OpenSsl; using Org.BouncyCastle.Crypto.Parameters; public class RSAPemReader { public static RSAParameters GetPublicKeyParametersWithCustomHeadersAndPKCS8(string pemFilePath) { using (StreamReader streamReader = new StreamReader(pemFilePath)) { PemReader pemReader = new PemReader(streamReader); RsaKeyParameters keyParams = (RsaKeyParameters)pemReader.ReadObject(); RSAParameters rsaParams = DotNetUtilities.ToRSAParameters(keyParams); return rsaParams; } } }

  7. C# Bouncy Castle read PEM RSA public key with passphrase: Description: This code demonstrates how to read a PEM-encoded RSA public key with passphrase protection using Bouncy Castle in C#.

    using System; using System.IO; using System.Security.Cryptography; using Org.BouncyCastle.OpenSsl; using Org.BouncyCastle.Crypto.Parameters; public class RSAPemReader { public static RSAParameters GetPublicKeyParametersWithPassphrase(string pemFilePath, string passphrase) { using (StreamReader streamReader = new StreamReader(pemFilePath)) { PemReader pemReader = new PemReader(streamReader, new PasswordFinder(passphrase)); RsaKeyParameters keyParams = (RsaKeyParameters)pemReader.ReadObject(); RSAParameters rsaParams = DotNetUtilities.ToRSAParameters(keyParams); return rsaParams; } } private class PasswordFinder : IPasswordFinder { private readonly string passphrase; public PasswordFinder(string passphrase) { this.passphrase = passphrase; } public char[] GetPassword() { return passphrase.ToCharArray(); } } }

  8. C# Bouncy Castle read PEM RSA public key with passphrase from string: Description: This code demonstrates how to read a PEM-encoded RSA public key with passphrase protection from a string using Bouncy Castle in C#.

    using System; using System.IO; using System.Security.Cryptography; using Org.BouncyCastle.OpenSsl; using Org.BouncyCastle.Crypto.Parameters; public class RSAPemReader { public static RSAParameters GetPublicKeyParametersWithPassphraseFromString(string pemString, string passphrase) { using (StringReader stringReader = new StringReader(pemString)) { PemReader pemReader = new PemReader(stringReader, new PasswordFinder(passphrase)); RsaKeyParameters keyParams = (RsaKeyParameters)pemReader.ReadObject(); RSAParameters rsaParams = DotNetUtilities.ToRSAParameters(keyParams); return rsaParams; } } private class PasswordFinder : IPasswordFinder { private readonly string passphrase; public PasswordFinder(string passphrase) { this.passphrase = passphrase; } public char[] GetPassword() { return passphrase.ToCharArray(); } } }

  9. C# Bouncy Castle read PEM RSA public key with passphrase from stream: Description: This code demonstrates how to read a PEM-encoded RSA public key with passphrase protection from a stream using Bouncy Castle in C#.

    using System; using System.IO; using System.Security.Cryptography; using Org.BouncyCastle.OpenSsl; using Org.BouncyCastle.Crypto.Parameters; public class RSAPemReader { public static RSAParameters GetPublicKeyParametersWithPassphraseFromStream(Stream stream, string passphrase) { using (StreamReader streamReader = new StreamReader(stream)) { PemReader pemReader = new PemReader(streamReader, new PasswordFinder(passphrase)); RsaKeyParameters keyParams = (RsaKeyParameters)pemReader.ReadObject(); RSAParameters rsaParams = DotNetUtilities.ToRSAParameters(keyParams); return rsaParams; } } private class PasswordFinder : IPasswordFinder { private readonly string passphrase; public PasswordFinder(string passphrase) { this.passphrase = passphrase; } public char[] GetPassword() { return passphrase.ToCharArray(); } } }

  10. C# Bouncy Castle read PEM RSA public key with passphrase using PEMReader: Description: This code demonstrates how to read a PEM-encoded RSA public key with passphrase protection using PEMReader from Bouncy Castle in C#.

    using System; using System.IO; using System.Security.Cryptography; using Org.BouncyCastle.OpenSsl; using Org.BouncyCastle.Crypto.Parameters; public class RSAPemReader { public static RSAParameters GetPublicKeyParametersWithPassphraseUsingPemReader(string pemFilePath, string passphrase) { using (StreamReader streamReader = new StreamReader(pemFilePath)) { PemReader pemReader = new PemReader(streamReader); pemReader.Password = passphrase; RsaKeyParameters keyParams = (RsaKeyParameters)pemReader.ReadObject(); RSAParameters rsaParams = DotNetUtilities.ToRSAParameters(keyParams); return rsaParams; } } }

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