I am struggling with the creation of a pfx file with Xamarin and BouncyCastle. I have the following settings/ specification
- .NET: PCL .Net Framework 4.5.1
- Xamarin: 4.5.0.476
- BouncyCastle: BouncyCastle-Signed 1.7.0.1 (NuGet Package)
I want to generate a Self-Signed Certificate for my mobile client to autheniticate itself against my server. The creation works pretty well using BouncyCastle. My problem is, when I want to store the certificate with its private key as a PKCS#12 (pfx) container and restore it from that container to send my web requests signed by it an exception is thrown telling me Input data cannot be coded as a valide certificate.
Here are the steps how i create my certificate, keys and store the pfx container.
Create the key pair:
private AsymmetricCipherKeyPair GenerateKeyPair()
{
var random = new SecureRandom();
var keyGenerationParameter = new KeyGenerationParameters(random, 4096);
var keyPairGenerator = new RsaKeyPairGenerator();
keyPairGenerator.Init(keyGenerationParameter);
var keyPair = keyPairGenerator.GenerateKeyPair();
return keyPair;
}
Create the certificate, which will call to create the keys and create the container:
public void CreateCertificate()
{
var random = new SecureRandom();
var keyPair = this.GenerateKeyPair();
// generate certificate generator and set public key.
var generator = new X509V3CertificateGenerator();
generator.SetPublicKey(keyPair.Public);
// generate and set serial number
BigInteger serialNumber = BigIntegers.CreateRandomInRange(BigInteger.One, BigInteger.ValueOf(long.MaxValue), random);
generator.SetSerialNumber(serialNumber);
// set signing algorithm.
generator.SetSignatureAlgorithm(Core.Constants.SignatureAlgorithmName);
// set name
string fullQualifiedName = $"CN=dummy,O=DummyOrg,OU=Dummy";
var name = new X509Name(fullQualifiedName);
generator.SetSubjectDN(name);
generator.SetIssuerDN(name);
// set valide time
generator.SetNotBefore(DateTime.UtcNow.AddHours(-1));
generator.SetNotAfter(DateTime.UtcNow.AddYears(10));
// add extensions.
var authorityKeyIdentifier = new AuthorityKeyIdentifier(
SubjectPublicKeyInfoFactory.CreateSubjectPublicKeyInfo(keyPair.Public).GetEncoded(),
new GeneralNames(new GeneralName(name)),
serialNumber);
var subjectKeyIdentifier = new SubjectKeyIdentifier(
SubjectPublicKeyInfoFactory.CreateSubjectPublicKeyInfo(keyPair.Public).GetEncoded());
generator.AddExtension(X509Extensions.AuthorityKeyIdentifier, false, authorityKeyIdentifier);
generator.AddExtension(X509Extensions.SubjectKeyIdentifier, false, subjectKeyIdentifier);
generator.AddExtension(X509Extensions.BasicConstraints.Id, true, new BasicConstraints(0));
// generate and validate certificate.
var cert = generator.Generate(keyPair.Private, random);
cert.CheckValidity(DateTime.UtcNow);
cert.Verify(keyPair.Public);
// generate pem string
using (var stringWriter = new StringWriter())
{
var writer = new PemWriter(stringWriter);
var pog = new PemObject("CERTIFICATE", cert.GetEncoded());
writer.WriteObject(pog);
// pem value
var value = stringWriter.ToString();
this.StoreCertificate(value);
}
// store the private key
using (var stringWriter = new StringWriter())
{
var writer = new PemWriter(stringWriter);
PrivateKeyInfo info = PrivateKeyInfoFactory.CreatePrivateKeyInfo(keyPair.Private);
var pog = new PemObject("RSA PRIVATE KEY", info.ToAsn1Object().GetEncoded());
writer.WriteObject(pog);
// pem value
var value = stringWriter.ToString();
this.StorePrivateKey(value);
}
try
{
this.CreatePfxFile();
}
catch (Exception ex)
{
throw;
}
}
Create the PFX container:
public void CreatePfxFile()
{
var certificate = this.GetCertificate();
var certEntry = new X509CertificateEntry(certificate);
string friendlyName = certificate.SubjectDN.ToString();
var privateKey = this.ReadPrivateKey();
PrivateKeyInfo info = PrivateKeyInfoFactory.CreatePrivateKeyInfo(privateKey);
byte[] keyBytes = info.ToAsn1Object().GetEncoded();
var store = new Pkcs12StoreBuilder().Build();
var keyEntry = new AsymmetricKeyEntry(privateKey, );
////store.SetCertificateEntry(Core.Constants.CertificateAlias, certEntry);
store.SetKeyEntry(Core.Constants.PrivateKeyAlias, new AsymmetricKeyEntry(privateKey), new X509CertificateEntry[] { certEntry });
MemoryStream stream = new MemoryStream();
store.Save(stream, Core.Constants.Password.ToCharArray(), new SecureRandom());
var pfxBytes = stream.ToArray();
var base64 = Convert.ToBase64String(pfxBytes);
this.StorePfxContainer(base64);
}
The methods GetCertificate() and ReadPrivateKey() will return an X509Certificate and an AsymmetricKeyParameter.
The method StorePfxContainer will just store the base64 string into a settings variable.
Note: I removed the line store.SetCertificateEntry(Core.Constants.CertificateAlias, certEntry); because it caused the pfx container to contain the certificate twice.
Please not, since now we are just using BouncyCastle stuff.
To sign my request i use the following code. The parameter cert will be created by retrieving the base64 string from the settings and use Convert.FromBase64String(settingsValue) to get the bytes.
private void SetCertificate(HttpWebRequest request, byte[] cert)
{
try
{
System.Security.Cryptography.X509Certificates.X509Certificate2 certificate =
new System.Security.Cryptography.X509Certificates.X509Certificate2(cert, Core.Constants.Password); // <-- throws the exception
request.ClientCertificates.Add(certificate);
}
catch (Exception ex)
{
string message = ex.Message;
}
}
Now we are using the Certificate from .Net (System.Security.Cryptography.X509Certificates.X509Certificate2). The exception which is thrown at the constructor of the x509Certifcate2 when I want to load the certificate is
Input data cannot be coded as a valide certificate thrown by Mono.Security
I tested the certificate and key with openssl, also i tried to generate a pfx container from my pem Certificate and pem private key, also works fine. Only when i load the certificate inside my code it will not work. So i think that the creation of the container has a bug which I haven't figured out by now.
Thanks for your help.
