Why the length of the data to encrypt is invalid?

Question

I using this class to perform AES encryption/decryption:

class Aes { static byte[] Key = { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f }; static byte[] IV = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }; public static byte[] Encrypt(string plainText) { byte[] encrypted; // Create a new AesManaged. using (AesManaged aes = new AesManaged()) { aes.Padding = PaddingMode.None; aes.Mode = CipherMode.ECB; // Create encryptor ICryptoTransform encryptor = aes.CreateEncryptor(Key, IV); // Create MemoryStream using (MemoryStream ms = new MemoryStream()) { // Create crypto stream using the CryptoStream class. This class is the key to encryption // and encrypts and decrypts data from any given stream. In this case, we will pass a memory stream // to encrypt using (CryptoStream cs = new CryptoStream(ms, encryptor, CryptoStreamMode.Write)) { // Create StreamWriter and write data to a stream using (StreamWriter sw = new StreamWriter(cs)) sw.Write(plainText); encrypted = ms.ToArray(); } } } // Return encrypted data return encrypted; } public static string Decrypt(byte[] cipherText/*, byte[] Key=Key, byte[] IV=IV*/) { string plaintext = null; // Create AesManaged using (AesManaged aes = new AesManaged()) { aes.Padding = PaddingMode.None; aes.Mode = CipherMode.ECB; // Create a decryptor ICryptoTransform decryptor = aes.CreateDecryptor(Key, IV); // Create the streams used for decryption. using (MemoryStream ms = new MemoryStream(cipherText)) { // Create crypto stream using (CryptoStream cs = new CryptoStream(ms, decryptor, CryptoStreamMode.Read)) { // Read crypto stream using (StreamReader reader = new StreamReader(cs)) plaintext = reader.ReadToEnd(); } } } return plaintext; } }

The problem is that when I encrypt using the following code I get the error: System.Security.Cryptography.CryptographicException: 'Length of the data to encrypt is invalid.'

var x = Aes.Encrypt(System.Text.Encoding.Default.GetString(new byte[] { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff })); Console.WriteLine(string.Join(", ", x.Select(b => b.ToString("X2"))));

I am trying to implement encrypted communication with a MSP432 microcontroller. According to this example, using these values:

Key: 000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f Plaintext: 00112233445566778899aabbccddeeff

I should get:

Ciphertext: 8ea2b7ca516745bfeafc49904b496089

Can someone tell me what I am doing wrong?

This code worked for me in .NET Core. What .NET are you using? — ingvar
– ingvar, Commented Aug 17, 2019 at 20:13
ECB mode does not require IV, though that is insecure to use. When your data size is not multiple of 16-byte you need a padding scheme as PKCS#7. PaddingMode.None means apply no padding, I'll deal with myself. So what will happen noew if you don't have multiple of 16-byte? — kelalaka
– kelalaka, Commented Aug 17, 2019 at 20:28
@kelalaka Using PKCS#7 and 15 bytes of plaintext, there is no error, but I need to obtain the values I mentioned in the question. — Cristian M
– Cristian M, Commented Aug 17, 2019 at 20:31

Cristian M · Accepted Answer · 2021-08-16 13:58:01Z

I managed to get it working using the following code:

 public byte[] encryptdata(byte[] bytearraytoencrypt, string key, string iv) { AesCryptoServiceProvider dataencrypt = new AesCryptoServiceProvider(); //Block size : Gets or sets the block size, in bits, of the cryptographic operation. dataencrypt.BlockSize = 128; //KeySize: Gets or sets the size, in bits, of the secret key dataencrypt.KeySize = 128; //Key: Gets or sets the symmetric key that is used for encryption and decryption. dataencrypt.Key = System.Text.Encoding.UTF8.GetBytes(key); //IV : Gets or sets the initialization vector (IV) for the symmetric algorithm dataencrypt.IV = System.Text.Encoding.UTF8.GetBytes(iv); //Padding: Gets or sets the padding mode used in the symmetric algorithm dataencrypt.Padding = PaddingMode.PKCS7; //Mode: Gets or sets the mode for operation of the symmetric algorithm dataencrypt.Mode = CipherMode.CBC; //Creates a symmetric AES encryptor object using the current key and initialization vector (IV). ICryptoTransform crypto1 = dataencrypt.CreateEncryptor(dataencrypt.Key, dataencrypt.IV); //TransformFinalBlock is a special function for transforming the last block or a partial block in the stream. //It returns a new array that contains the remaining transformed bytes. A new array is returned, because the amount of //information returned at the end might be larger than a single block when padding is added. byte[] encrypteddata = crypto1.TransformFinalBlock(bytearraytoencrypt, 0, bytearraytoencrypt.Length); crypto1.Dispose(); //return the encrypted data return encrypteddata; } //code to decrypt data private byte[] decryptdata(byte[] bytearraytodecrypt, string key, string iv) { AesCryptoServiceProvider keydecrypt = new AesCryptoServiceProvider(); keydecrypt.BlockSize = 128; keydecrypt.KeySize = 128; keydecrypt.Key = System.Text.Encoding.UTF8.GetBytes(key); keydecrypt.IV = System.Text.Encoding.UTF8.GetBytes(iv); keydecrypt.Padding = PaddingMode.PKCS7; keydecrypt.Mode = CipherMode.CBC; ICryptoTransform crypto1 = keydecrypt.CreateDecryptor(keydecrypt.Key, keydecrypt.IV); byte[] returnbytearray = crypto1.TransformFinalBlock(bytearraytodecrypt, 0, bytearraytodecrypt.Length); crypto1.Dispose(); return returnbytearray; }

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