We Keep Coding

Example code PHP / C# AES encryption - random IV

I found an implementation for AES encryption/decryption that's supposed to work in PHP and C#:
https://odan.github.io/2017/08/10/aes-256-encryption-and-decryption-in-php-and-csharp.html
However, in this example, the IV is always 0, which is not good.
So, as the author suggests, I use the openssl_random_pseudo_bytes() function:
$ivlen = openssl_cipher_iv_length($method);
$iv = openssl_random_pseudo_bytes($ivlen);
However, the problem now is, that I have to store the IV somewhere so that the C# app can use it for decryption. My idea was to base64_encode it and prepend it to the encrypted message with ":" separating both, so that I can simply split the string, then base64 decode it in C# and can use the IV. However, this does not work. This is the code:
public string DecryptString(string cipherText, byte[] key, byte[] iv)
{
// Instantiate a new Aes object to perform string symmetric encryption
Aes encryptor = Aes.Create();
encryptor.Mode = CipherMode.CBC;
// Set key and IV
byte[] aesKey = new byte[32];
Array.Copy(key, 0, aesKey, 0, 32);
encryptor.Key = aesKey;
encryptor.IV = iv;
// Instantiate a new MemoryStream object to contain the encrypted bytes
MemoryStream memoryStream = new MemoryStream();
// Instantiate a new encryptor from our Aes object
ICryptoTransform aesDecryptor = encryptor.CreateDecryptor();
// Instantiate a new CryptoStream object to process the data and write it to the
// memory stream
CryptoStream cryptoStream = new CryptoStream(memoryStream, aesDecryptor, CryptoStreamMode.Write);
// Will contain decrypted plaintext
string plainText = String.Empty;
try {
// Convert the ciphertext string into a byte array
byte[] cipherBytes = Convert.FromBase64String(cipherText);
// Decrypt the input ciphertext string
cryptoStream.Write(cipherBytes, 0, cipherBytes . Length);
// Complete the decryption process
cryptoStream.FlushFinalBlock();
// Convert the decrypted data from a MemoryStream to a byte array
byte[] plainBytes = memoryStream.ToArray();
// Convert the decrypted byte array to string
plainText = Encoding.ASCII.GetString(plainBytes, 0, plainBytes.Length);
} finally {
// Close both the MemoryStream and the CryptoStream
memoryStream.Close();
cryptoStream.Close();
}
// Return the decrypted data as a string
return plainText;
}
And this is how I try to call the function with the IV prepended to the encrypted message:
private void btnDecrypt_Click(object sender, EventArgs e)
{
string encrypted = txtEncrypted.Text;
string password = txtPW.Text;
string[] temp = encrypted.Split(":".ToCharArray());
string iv_str = temp[0];
encrypted = temp[1];
SHA256 mySHA256 = SHA256Managed.Create();
byte[] key = mySHA256.ComputeHash(Encoding.ASCII.GetBytes(password));
iv_str = Encoding.Default.GetString(Convert.FromBase64String(iv_str));
byte[] iv = Encoding.ASCII.GetBytes(iv_str);
txtDecrypted.Text = this.DecryptString(encrypted, key, iv);
}
Doesn't work. It decrypts something, but that's just gibberish and not the message I encrypted in PHP.
I think it has to do with the IV somehow.

#Topaco:
Thank you very much... now I see what my mistake was. It works now with generated IV.
By the way, two more questions on the strength of the encryption:
Is it ok to use the following function to generate an IV (GenerateIV() for some reason won't work):
byte[] iv = new byte[16];
Random rnd = new Random();
rnd.NextBytes(iv);
I added a randomly generated salt to the password of the user, so that the key is a hash from the user password and a salt. I also prepend the salt, together with the now randomly generated IV, to the message. Then for the decryption process I use the prepended salt and the key the user enters. Works so far. But does it weaken the encryption? No, right?
Thank you very much.
// Edit: Code format doesn't work, don't know why.

Invalid Cipher Text Exception while decrypting AES key using RSA

I'm working on encrypt/decrypt request/response on both angular 6 and .net core api side. I'm encrypting data in angular using AES and encrypting AES key using RSA public key and sending it to .net core api. I have created action filter to decrypt the request, and to decrypt the request first I have to decrypt the AES key using RSA private key but it is giving me an error while decrypting AES key using RSA private key:
ex {Org.BouncyCastle.Crypto.InvalidCipherTextException: block incorrect
at Org.BouncyCastle.Crypto.Encodings.Pkcs1Encoding.DecodeBlock(Byte[] input, Int32 inOff, Int32 inLen)
at Phyzii.Core.Api.Security.RSA.Decrypt(String cipherText)} System.Exception {Org.BouncyCastle.Crypto.InvalidCipherTextException}
Here is my RSA encryption code at angular side:
import JSEncrypt from 'jsencrypt';
encryptObj = new JSEncrypt();
transitionIn(data: any) {
this.aesSecretKey=this.makeUniqueKey(10);
console.log(this.aesSecretKey);
this.data.DATAOBJ = this.aesEncrypt(this.aesSecretKey, data);
this.encryptObj.setPublicKey(this.publicKeyClient);
this.data.KEY = this.encryptObj.encrypt(this.aesSecretKey);
return this.data;
}
Here is my RSA decryption code at C# side:
private static AsymmetricCipherKeyPair ReadPemFile(string flag)
{
string filePath = flag == "PUBLIC" ? "D:/Crypto/private_key.pem" : "D:/Crypto/private_key_server.pem";
AsymmetricCipherKeyPair keys;
using (var reader = File.OpenText(filePath))// file containing RSA PKCS1 private key
keys = (AsymmetricCipherKeyPair)new PemReader(reader).ReadObject();
AsymmetricKeyParameter private_key = keys.Private;
AsymmetricKeyParameter public_key = keys.Public;
return keys;
}
//cipherText = "gOItOryuGy0UXHfoNqo0omcXLIOS6dhLJas5zeDNA7MfvsHYwP4ccSWU9JwTrIRiYUq/NB9oRn62ZQ5ynDnsGXUmHfVT4oPxtQZE1fXTTMN5ycfgthegesmXoZMMcWxA/wnwjLAgE17MNaunKY307W+nyc3jEMT1QsWUoOBESo0="
public static string Decrypt(string cipherText)
{
try
{
byte[] cipherTextBytes = Convert.FromBase64String(cipherText);
AsymmetricCipherKeyPair keys = ReadPemFile("PRIVATE");
AsymmetricKeyParameter private_key = keys.Private;
// Pure mathematical RSA implementation
// RsaEngine eng = new RsaEngine();
// PKCS1 v1.5 paddings
// Pkcs1Encoding eng = new Pkcs1Encoding(new RsaEngine());
// PKCS1 OAEP paddings
Pkcs1Encoding eng = new Pkcs1Encoding(new RsaEngine());
eng.Init(false, private_key);
int length = cipherTextBytes.Length;
int blockSize = eng.GetInputBlockSize();
List<byte> plainTextBytes = new List<byte>();
for (int chunkPosition = 0; chunkPosition < length; chunkPosition += blockSize)
{
int chunkSize = Math.Min(blockSize, length - chunkPosition);
plainTextBytes.AddRange(eng.ProcessBlock(cipherTextBytes, chunkPosition, chunkSize));
}
return Encoding.UTF8.GetString(plainTextBytes.ToArray());
}
catch (Exception ex)
{
throw ex;
}
}
and If i set true in Pkcs1Encoding Init
Pkcs1Encoding eng = new Pkcs1Encoding(new RsaEngine());
eng.Init(true, private_key);
Then it is decrypting data in this format �����Ŧ���%�Rc��\u000e�\b\u0004����I�]&P~�+�뛡�^s�V�ʗ' \b��?Jv�F�ge\u001b�S���^�\u0002��v/|�vh�}�z�[A�}��\u0002u\\�Pp����\u0011k9\u001e\n�E\b�\u0003��\u001a#��}��y��\u000eTG�U\a�A_KV�\u007fs����?3���*/*\n\n~�w�Q��'��\a:���q��BH\u0004R�#c��'d�\u001f���\0 5\u007f���fs�<���\u0012\t����|�[\u0015\b+��8\u0003�[�v����Ǹ��8ځ\u001cԞv�{=���#-o\u0004�I\u0014J�\0#4`
which is incorrect,
what can be the issue?

OpenSSL encryption failing to decrypt C#

I have been struggling with decrypting some data that is being encrypted on a Unix machine via SSL, I keep getting padding errors, and am unsure what it is that I am missing.
The encrypted file is a simple text file just saying "Hello World".
The encryption command used in unix is:
openssl enc -base64 -aes-256-cbc -k 12345678901234567890123456789012 -in test.txt -out cbc64.txt
I have 2 methods that I am using to decrypt:
private static CipherMode sCipherMode = CipherMode.CBC;
private static PaddingMode sPaddingMode = PaddingMode.PKCS7;
private const int HigKeyLen = 32;
private const int HigKeySiz = 256;
public static string decrypt(string text, //the text to be decrypt
int cipherindex// the strength of the original encryption
)
{
byte[] plainText = null;
try
{
string tempText = Regex.Replace(text, #"\n", "");
//get the cipher strength--from cipherindex
CipherKey Key = CipherKey.getCipherKey(cipherindex);
//build and init the Decryptor
RijndaelManaged rijndaelCipher = new RijndaelManaged();
rijndaelCipher.Mode = sCipherMode;
rijndaelCipher.Padding = sPaddingMode;
rijndaelCipher.KeySize = Key.Size;
rijndaelCipher.BlockSize = Key.Size;
byte[] encryptedData = Convert.FromBase64String(tempText);
byte[] pwdBytes = System.Text.Encoding.UTF8.GetBytes(pass);
byte[] keyBytes = new byte[Key.Len];
int len = pwdBytes.Length;
if (len > keyBytes.Length)
{
len = keyBytes.Length;
}
Array.Copy(pwdBytes, keyBytes, len);
rijndaelCipher.Key = keyBytes;
rijndaelCipher.IV = keyBytes;
ICryptoTransform transform = rijndaelCipher.CreateDecryptor();
plainText = transform.TransformFinalBlock(encryptedData, 0, encryptedData.Length);
}
catch (Exception e)
{
// test code, do nothing
}
return System.Text.Encoding.UTF8.GetString(plainText);
}
This returns the following error: Padding is invalid and cannot be removed.
The second method:
public static string Decryptor(string TextToDecrypt)
{
byte[] EncryptedBytes = Convert.FromBase64String(Regex.Replace(TextToDecrypt, #"\n", ""));
//Setup the AES provider for decrypting.
AesCryptoServiceProvider aesProvider = new AesCryptoServiceProvider();
//aesProvider.Key = System.Text.Encoding.ASCII.GetBytes(strKey);
//aesProvider.IV = System.Text.Encoding.ASCII.GetBytes(strIV);
aesProvider.BlockSize = 128;
aesProvider.KeySize = 256;
//My key and iv that i have used in openssl
aesProvider.Key = System.Text.Encoding.UTF8.GetBytes(pass);
aesProvider.IV = System.Text.Encoding.UTF8.GetBytes(pass);
aesProvider.Padding = PaddingMode.PKCS7;
aesProvider.Mode = CipherMode.CBC;
ICryptoTransform cryptoTransform = aesProvider.CreateDecryptor(aesProvider.Key, aesProvider.IV);
byte[] DecryptedBytes = cryptoTransform.TransformFinalBlock(EncryptedBytes, 0, EncryptedBytes.Length);
return System.Text.Encoding.ASCII.GetString(DecryptedBytes);
}
The second method gives an issue due to the password not being the right length for the blocksize.
What is it that I am doing wrong?

You openssl command is wrong, I assume it should be:
openssl enc -base64 -aes-256-cbc -k 12345678901234567890123456789012 -in test.txt -out cbc64.txt
reading your code I see you made a few wrong assumptions:
You are using the password as a key and as IV (where did you get that?)
Password is not key
you've assumed the output is pure ciphertext
try to add -p parameter to the openssl enc command and it will display as well salt and derived key and iv
So lets fix that:
OpenSSL generates random 8 bytes salt
OpenSSL uses its "magic" function EVP_BytesToKey to derive the key and IV from the passsword and salt, example impl in c#
OpenSSL output looks like: base64(Salted_{salt}{ciphertext})

Hybrid cryptosystem implementation in .net. Error Specified key is not a valid size for this algorithm

I am trying to implement hybrid cryptosystem as mentioned in https://en.wikipedia.org/wiki/Hybrid_cryptosystem
At the moment I have implemented following algorithm
private void button1_Click(object sender, EventArgs e)
{
CspParameters cspParams = new CspParameters { ProviderType = 1 };
RSACryptoServiceProvider rsaProvider = new RSACryptoServiceProvider(1024, cspParams);
string publicKey = Convert.ToBase64String(rsaProvider.ExportCspBlob(false));
string privateKey = Convert.ToBase64String(rsaProvider.ExportCspBlob(true));
string symmericKey = "Kamran12";
txtEncryptedData.Text = EncryptData(txtInputData.Text, symmericKey);
string encryptedsymmetrickey = EncryptData(symmericKey, publicKey); //error line
//string decryptsymmetrickey = encryptedsymmetrickey + privateKey;
//string decrypteddata = encryptedData + decryptsymmetrickey;
}
public string EncryptData(string data, string key)
{
string encryptedData = null;
byte[] buffer = Encoding.UTF8.GetBytes(data);
DESCryptoServiceProvider desCryptSrvckey = new DESCryptoServiceProvider
{
Key = new UTF8Encoding().GetBytes(key)
};
desCryptSrvckey.IV = desCryptSrvckey.Key;
using (MemoryStream stmCipherText = new MemoryStream())
{
using (CryptoStream cs = new CryptoStream(stmCipherText, desCryptSrvckey.CreateEncryptor(), CryptoStreamMode.Write))
{
cs.Write(buffer, 0, buffer.Length);
cs.FlushFinalBlock();
encryptedData = Encoding.UTF8.GetString(stmCipherText.ToArray());
}
}
return encryptedData;
}
But getting error Specified key is not a valid size for this algorithm. at the time of encrypting the symmetric key

You are trying to encrypt using the (insecure) DES algorithm with an RSA public key. That's always going to fail, DESCryptoServiceProvider doesn't accept RSA keys. You'd need an RSACryptoServiceProvider for that.
You may want to consider using a specific library that already implements hybrid cryptography (PGP, CMS or one of the proprietary protocols). The way you are going at it your solution may run in the end, but it will not be secure.

Aes Encrypt and Decrypt null adds bytes

Hi there i'm using this encryption method to encrypt my json value in .net side
public static string Encrypt256(string text)
{
AesCryptoServiceProvider aes = new AesCryptoServiceProvider();
aes.BlockSize = 128;
aes.KeySize = 256;
aes.IV = Encoding.UTF8.GetBytes(AesIV256);
aes.Key = Encoding.UTF8.GetBytes(AesKey256);
aes.Mode = CipherMode.CBC;
byte[] src = Encoding.Unicode.GetBytes(text);
using (ICryptoTransform encrypt = aes.CreateEncryptor())
{
byte[] dest = encrypt.TransformFinalBlock(src, 0, src.Length);
Debug.WriteLine(Convert.ToBase64String(dest));
return Convert.ToBase64String(dest);
}
}
And im trying to decrypt it in Node Js side
var crypto = require('crypto'),
algorithm = process.env.tombalaCryptoAlgorithm,
password = process.env.tombalaHmacPass,
iv = '!QAZ2WSX#EDC4RFV'
function encrypt(text) {
var cipher = crypto.createCipheriv(algorithm, password, iv)
var encrypted = cipher.update(text, 'utf8', 'base64')
encrypted += cipher.final('base64');
return encrypted;

You are converting your text to be encrypted to Unicode which means UTF-16.
In UTF-16 every character consists of two bytes. If the second byte is not used it is null as you have observed.
I assume you want UTF-8 encoding. Therefore replace the line
byte[] src = Encoding.Unicode.GetBytes(text);
with
byte[] src = Encoding.UTF8.GetBytes(text);