Decrypting in Python an string encrypted using .NET
.net, c#, encryption, python, string
Solution
The string is encoded to bytes using the UTF-16 encoding. The first two bytes are a BOM. Then each character is encoded to two bytes.
From the documentation for `Encoding.Unicode`:
Gets an encoding for the UTF-16 format using the little endian byte order.
To get the original string you need to decode it back from UTF-16 bytes to a Unicode string.
print aes.decrypt(text).decode('utf-16')
Problem
I am trying to encrypt a string using C# and decrypt it using Python. The encryption/decryption part works as expected (i.e. I am able to decrypt the string I originally encrypted). However the string returned by Python has 2 extra bytes at the beginning and each character is separated by a space. ``` **Original string** (before encryption -- encrypted using C#) = "Something you want to keep private with AES" **Decrypted string** (using Python) = "��S o m e t h i n g y o u w a n t t o k e e p p r i v a t e w i t h A E S" ``` Why am I getting these two extra bytes at the beginning of the string? Why all those spaces in the decrypted string? Any idea why? Thanks! Encryption with C# ``` public static string Encrypt<T>(string value, string password, string salt) where T : SymmetricAlgorithm, new() { DeriveBytes rgb = new Rfc2898DeriveBytes(password, Encoding.Unicode.GetBytes(salt)); SymmetricAlgorithm algorithm = new T(); byte[] rgbKey = rgb.GetBytes(algorithm.KeySize >> 3); byte[] rgbIV = rgb.GetBytes(algorithm.BlockSize >> 3); ICryptoTransform transform = algorithm.CreateEncryptor(rgbKey, rgbIV); using (MemoryStream buffer = new MemoryStream()) { using (CryptoStream stream = new CryptoStream(buffer, transform, CryptoStreamMode.Write)) { using (StreamWriter writer = new StreamWriter(stream, Encoding.Unicode)) { writer.Write(value); } } return Convert.ToBase64String(buffer.ToArray()); } } string plain = "Something you want to keep private with AES"; string encrypted = CipherUtility.Encrypt<AesManaged>(plain, "password", "salt"); ``` Decryption with Python + pycrypto ``` import base64, sys import Crypto.Cipher.AES password = base64.b64decode('PSCIQGfoZidjEuWtJAdn1JGYzKDonk9YblI0uv96O8s=') # See rgbKey salt = base64.b64decode('ehjtnMiGhNhoxRuUzfBOXw==') # See rgbIV aes = Crypto.Cipher.AES.new(password, Crypto.Cipher.AES.MODE_CBC, salt) text = base64.b64decode('QpHn/fnraLswwI2Znt1xTaBzRtDqO4V5QI78jLOlVsbvaIs0yXMUlqJhQtK+su2hYn28G2vNyLkj0zLOs+RIjElCSqJv1aK/Yu8uY07oAeStqRt4u/DVUzoWlxdrlF0u') print aes.decrypt(text) ```