I have a small inhouse app (and any advice on other methods is appreciated as well) where I utilize 2 token strings that I'd like to encrypt with aes. While this is a super small app and I don't think there's a huge risk on my local, I'd still like to encrypt them with something. My thought was that I'd:
have a file on my local with the iv/key string that I could read into my app upon running, it'd decrypt the token which is stored in the db and I could use it, and when I have to overwrite the token value I'd create a new aes/triple dev iv/key pair. the iv/key pair lives in a file (or the config of the app) and then the new encrypted token goes to my db.
The problem I'm having (i'm new to encryption) is that all of the tutorials show something like the following:
Aes aes = Aes.Create();
byte[] iv = aes.IV;
byte[] key = aes.Key;
However I'm looking to store the string value, and then when the app runs next and I pull the iv/key pair in I convert it back to byte[] to do the app work.
I tried:
string ivStr = Encoding.Default.GetString(iv);
However when I tried to convert it back to a byte[] and then pass it back through to the decryption tool it would just fail and told me the length of the array was incorrect.
Any advice on this would be appreciated.
Related
I am hoping that this question can be met with some guidance for someone who is beginning to work with encryption/decryption in C#. There are existing examples on the web regarding this, but I am truthfully struggling to put it all into practice for my given situation.
If given a text file that has been encrypted using OpenPGP with RSA, what is the best method to decrypt this in C#?
This is what I am attempting:
Using Kleopatra OpenPGP, I am generating a key pair using 2048bit RSA. This generates a private and public key.
I am then encrypting/signing a text file with a few word in it as a test.
In C#, I want to decrypt this text file.
Current code:
byte[] encryptedData = File.ReadAllBytes("C:\\PGP Encryption\\test.txt.gpg"); // The encrypted text file generated by Kleopatra.
using (RSACryptoServiceProvider RSA = new RSACryptoServiceProvider())
{
//Import the RSA Key information. This needs
//to include the private key information.
RSA.ImportParameters(RSAKeyInfo);
//Decrypt the passed byte array and specify OAEP padding.
decryptedData = RSA.Decrypt(DataToDecrypt, DoOAEPPadding);
}
return decryptedData;
Unfortunately, the RSA.Decrypt() call throws an exception that reads "The data to be decrypted exceeds the maximum for this modulus of 128 bytes."
I also do not believe that my private key is actually being loaded, as I'm not explicitly stating where the key is. But I don't see how the RSAParameters object is supposed to get populated otherwise.
If anyone can point me in the right direction to decrypt a file in this way, thank you in advance for your time and information.
It's looks like you need this library (see Decrypt section) https://github.com/mattosaurus/PgpCore
I'm trying to write a service to SFTP to a server on a given interval, download all files in a directory, and then decrypt them for processing.
The decrypt method was working at one point, and I have no modified it since. I am still using the same keys as when it did successfully work.
I am using the PGPEncrypt, PGPDecrypt, and PGPEncryptionKeys classes for BouncyCastle found here: https://github.com/sledwith/PGP-Decryption-With-C-Sharp
Additionally, I have modified the code as shown here: Exception on decrypting file using BouncyCastle PGP
If you noticed, I commented on how that fixed my code and the decryption worked.
Now, it isn't.
Does anyone have some insight why this might have happened, or how I could go about fixing it?
I am going to make a guess that you are using a 1024 bit RSA public/private key and trying to encrypt 128 bytes of something with it? If I am right, use a larger RSA key (RSA 4096 will allow you to encrypt up to ~500 bytes).
I note in the linked post you say this is sporadic. Some googling indicates that if you have leading zeros in the to-be-encrypted bytes it may be able to handle a full 128 bytes.
Also - if you are just encrypting "data" with the keypair, you need to be certain it will not overrun these limitations (240 or so bytes for RSA 2048 and 500 or so for RSA 4096 accounting for padding). Good practice and future proofing would be to implement a symmetric key encryption of all your data and just use the RSA key to encrypt / decrypt your keys.
If you're not dead-set on using the PGP process explicitly, you might use my library here:
https://github.com/zenith-nz/ObscurCore
Its "banner feature" is not yet fully active (creating encrypted archives of a kind), but it does everything that you want it for, it appears - it does key derivation with a ECDHC scheme, UM1, and implements a large variety of block and stream ciphers. It's built on top of BouncyCastle.
I think I resolved this problem; please try this code.
public string StringToDecrypt(string text)
{
byte[] toDecrypt = Convert.FromBase64String(text);
AsymmetricCipherKeyPair keyPair;
using (var reader = File.OpenText(#"Private Key File Path"))
{
keyPair = (AsymmetricCipherKeyPair) new PemReader(reader).ReadObject();
}
var engine = new RsaEngine();
engine.Init(false, keyPair.Private);
return Encoding.UTF8.GetString(engine.ProcessBlock(toDecrypt, 0, toDecrypt.Length));
}
We encrypt PDFs using AESManaged algorithm implemented in .NET framework. I used the example explained in here to implement C# code to encrypt the file. Now I need to decrypt that file using an iPhone application.(That is the requirement). So I use the this code to do that but decryption failed by returning an error.
'Error Domain=CommonCryptoErrorDomain Code=-4304 "Decode Error"
UserInfo=0x127356c0 {NSLocalizedFailureReason=Input data did not
decode or decrypt correctly, NSLocalizedDescription=Decode Error'
Can some one help me to resolve this issue.
We use 12345678 as encryption key.
Most likely the problem is in the deriving actual key from the password (12345678 cannot be the AES key directly - it is only 8 bytes).
Technically this should work though I've never tested it, both methods uses the same ad-hoc format.
Encrypt using my authenticated encryption example.
//use your secret data you want to encrypt instead.
String secretMessage = "Message";
var rnCryptorHeader = new Byte[]{
2, //RNCryptor Format version 2
0 //RNCryptor Uses password
};
//encryptedString is base64 encoded
var encryptedString = AESThenHMAC.SimpleEncryptWithPassword(secretMessage,
password:"1234567891011",
nonSecretPayload:rnCryptorHeader);
Then Decrypt using RNCryptor and NSData+Base64 for IOS
//This is the encrypted data passed from .net
NSString *encryptedString = #"AgE8C9E7gsfyOAmSotIOgyLQ0O6mdcuMXXjN/iZa3azym4KVWZAkfykIP6mqMt/qkpfftdB3XQhMkoxtQEM+rA0iHxOvZiNlmA2KJtg6BOnmlg==";
NSData *encryptedData = [NSData dataFromBase64String: encryptedString];
NSError *error;
NSData *decryptedData = [RNDecryptor decryptData:encryptedData
withPassword:#"1234567891011"
error:&error];
NSString *secretMessage = [[[NSString alloc] initWithData:decryptedData
encoding:NSUTF8StringEncoding] autorelease];
Since you aren't dealing with strings and are dealing with bytes directly, just remove the Base64 and utf8 encoding/decoding from this objective-c example and the linked c# example, once you are sure this is working.
After looking at how to generate self-signed digital signatures from Creating a self-signed certificate in C#, I can call CreateSelfSignCertificatePfx and get PXF data in a byte array back, which can then be used within an X509Certificate2 object to sign and verify. Example...
byte[] pfx = Certificate.CreateSelfSignCertificatePfx("O=Company,CN=Firstname,SN=Lastname", DateTime.Now, DateTime.Now.AddYears(1), "password");
X509Certificate2 cert = new X509Certificate2(pfx, "password");
byte[] publicBytes = cert.RawData;
RSACryptoServiceProvider rsa = (RSACryptoServiceProvider)cert.PrivateKey;
byte[] signedData = rsa.SignData(new System.Text.UTF8Encoding().GetBytes("Test"), new SHA1CryptoServiceProvider());
RSACryptoServiceProvider rsa2 = (RSACryptoServiceProvider)new X509Certificate2(publicBytes).PublicKey.Key;
bool verified = rsa2.VerifyData(new System.Text.UTF8Encoding().GetBytes("Test"), new SHA1CryptoServiceProvider(), signedData);
This works. My concern though is the original bytes, byte[] pfx from above, need to be stored in a DB (to sign stuff). The question becomes, how secure are the bytes in this format? I know you need the password to construct the new X509Certificate2 with a private key, but in a general sense, how secure are the bytes without the password? I have no problems encrypting these bytes as an added layer, but is that necessary?
According to X509Certificate2.X509Certificate2(Byte[], String) Constructor
Calling this constructor with the correct password decrypts the private key and saves it to a key container.
I just want to ensure the private key is safe without the password.
In my eyes the question is not whether you should put the "bytes" in the database, but more, would you put the file with the private key in your file system.
In the way you're doing it, it's essentially the same thing. You're just storing the bytes that make up the cert file.
I may be failing to understand the difference here, but they bytes and the file are essentially the same thing, the only difference being the fact that one has to gain access to the db to get them.
Use a smartcard or token to store your private key.
UPDATE:
The Pvt key can be accessed by anyone who can access the machine.
The private keys in a PFX (PKCS#12) are stored encrypted, which is of course what the password is for. Not all of a PFX is encrypted, the structural pieces stay plaintext to contain metadata about the contents (like what encryption algorithm was used).
Based on inspecting the file, as of Windows 7 the private keys are encrypted using 3-key (168-bit) 3DES. The key is derived via a complex formula involving your password; there's nothing saved in the file which gives any indication as to what your password was, how long it was, et cetera.
The password is usually proven correct by the addition of a MAC on the contents, which uses the same password for its key derivation function. In the possible case of the MAC password and the encryption password being different (which I've personally never seen) the password is verified by the structural information in the encrypted payload.
DES' weakness mainly lay in the small keysize, it's easily brute forcable today. A 3-key 3DES key has 112 more semantic bits than a (1)DES key, making it take 2^112 (~5 x 10^33) times longer to break.
So, at the end of the day, the private key is cryptographically sound. But like anything with a password-based input, if you use a bad password that is easily guessed then it can be cracked by brute force.
Here is the problem I am trying to solve. Let's say I was releasing some web software built on ASP.NET MVC and I only wanted the end user to be able to add X users to the system. The software would be hosted on their servers.
I want to include an encrypted file that when the user tries to add a new user, it goes out and reads from the file an encrypted string. When the website decodes it, the clear text will be the number of allowed users.
What is the best/simplest way on my end to encrypt to generate this string on my end then decode it back to clear text in my application? Obviously I want to ensure that the end user cannot be spinning up their own encrypted string and just replace mine. I don't want to worry about having to try and obfuscate my source so that they would not be able to see how I decode the string.
Is it possible to encrypt with a private rsa key, then decrypt it with the public one? I haven't had luck with that in the code below:
var rsa = new RSACryptoServiceProvider();
var pubicKey = rsa.ToXmlString(false);
var privateKey = rsa.ToXmlString(true);
var test = "this string needs to be encrypted then decrypted";
var rsa2 = new RSACryptoServiceProvider();
rsa2.FromXmlString(privateKey);
var encryptedBytes = rsa2.Encrypt(Encoding.UTF8.GetBytes(test), false);
var encryptedString = Convert.ToBase64String(encryptedBytes);
var rsa3 = new RSACryptoServiceProvider();
rsa3.FromXmlString(pubicKey);
encryptedBytes = Convert.FromBase64String(encryptedString);
var decryptedString = Encoding.UTF8.GetString(rsa3.Decrypt(encryptedBytes, false));
You can use a signature strategy, where the private key is used to generate a signature that verifies that your message is authentic.
// Create message and signature on your end
string message = "Here is the license message";
var converter = new ASCIIEncoding();
byte[] plainText = converter.GetBytes(secret);
var rsaWrite = new RSACryptoServiceProvider();
var privateParams = rsaWrite.ExportParameters(true);
// Generate the public key / these can be sent to the user.
var publicParams = rsaWrite.ExportParameters(false);
byte[] signature =
rsaWrite.SignData(plainText, new SHA1CryptoServiceProvider());
// Verify from the user's side. Note that only the public parameters
// are needed.
var rsaRead = new RSACryptoServiceProvider();
rsaRead.ImportParameters(publicParams);
if (rsaRead.VerifyData(plainText,
new SHA1CryptoServiceProvider(),
signature))
{
Console.WriteLine("Verified!");
}
else
{
Console.WriteLine("NOT verified!");
}
This example was largely copied from Microsoft's site:
RSACryptoServiceProvider.SignData Method (Byte[], Object)
And here is web page that explains the concept:
Using RSA for Signing Messages
I think what you are looking for is digital signature. It doesn't matter if the content is encrypted or not, since the user has the (public) key to decrypt it. All that matters is if the content's source is you.
Since you have a config file I reckon it is XML, so you are looking for XMLDSIG.
You can easily achieve this using the SignedXml class in .Net. Then all you need to do is verify the signature when loading the config file. This method allows you to eaisly use any X509 certificates you may have. You can even embed the public key in the signed file, so the user does not need to install your cert (public key).
Your idea is correct, but I wonder about unforeseen consequences.
You state they will be running software on their servers, so this means they are hosting a service for themselves. But you also mention this service has to connect out tot he internet to add a user by validating with your server. What happens when the internet goes down or they want to have a secure system and a firewall blocks internet access to the servers? Will they completely lose their ability to function?
Just giving you a question to ask yourself :p
You don't use a public key to 'decrypt' the file. you can only decrypt the file with the private key.
In your case you could store the number of users as well a signature of the data which you create with your private key.
On the clients sever, you use your public key to verify the signature matches the data in the file (number of users)
However, it is possible that an advanced user could swap out your public key with their own and sign the file themselves.
As stated in your comment in the question, your approach is using a key from a client and a key from yourself. This will not work, as the prime numbers used in RSA are meant for use with only the corresponding private/public key.
What you need to do use your two keys and nothing from the client or the client's two keys and nothing of yours. For example,
You could sign it using your two keys by encrypting with your private key and allowing the client to decrypt using your public key.
You could encrypt it using your client's public key and have them decrypt is using their (the client's) private key.
Hope this helps!