We Keep Coding

How do you create SHA-2 and AES encrypted string to use in HTTP request header in .NET?

I am trying to write client code that requests for information from an external API over the web.
The API is simple enough (to me) except for the stipulations of how to generate the authorisation key.
First some context:
There are 6 string values required to start with:
token
password
devId
salt
orgId
givenKey
Now for the encryption stuff. First up SHA2.
hashedString = SHA2(token + password + devId)
Followed by AES.
authKey = AES(salt + orgId + "=" + hashedString)
The AES parameters are specified as follows:
Mode = ECB
Padding = PKCS5Padding
Secret Key = givenKey
My problem is that I know next to nothing about cryptography.
Below is the code I have attempting to accomplish the above.
// Generate Authorisation key
byte[] fieldsBytes = Encoding.ASCII.GetBytes(token + password + devId);
byte[] keyBytes = Encoding.ASCII.GetBytes(secretKey);
SHA512 shaM = new SHA512Managed();
string hashedFields = Encoding.ASCII.GetString(shaM.ComputeHash(fieldsBytes));
byte[] encryptedBytes = EncryptStringToBytes_Aes(salt + orgId + "=" + hashedfields,
keyBytes, keyBytes);
string encryptedString = Encoding.ASCII.GetString(encryptedBytes);
private byte[] EncryptStringToBytes_Aes(string plainText, byte[] Key, byte[] IV)
{
// Check arguments.
if (plainText == null || plainText.Length <= 0)
throw new ArgumentNullException("plainText");
if (Key == null || Key.Length <= 0)
throw new ArgumentNullException("Key");
if (IV == null || IV.Length <= 0)
throw new ArgumentNullException("IV");
byte[] encrypted;
// Create an Aes object
// with the specified key and IV.
using (Aes aesAlg = Aes.Create())
{
aesAlg.Key = Key;
aesAlg.IV = IV;
aesAlg.Padding = PaddingMode.PKCS7;
aesAlg.Mode = CipherMode.ECB;
// Create an encryptor to perform the stream transform.
ICryptoTransform encryptor = aesAlg.CreateEncryptor();
// Create the streams used for encryption.
using (MemoryStream msEncrypt = new MemoryStream())
{
using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
{
using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
{
//Write all data to the stream.
swEncrypt.Write(plainText);
}
encrypted = msEncrypt.ToArray();
}
}
}
// Return the encrypted bytes from the memory stream.
return encrypted;
}
This code gets a "401" from the external service.
My first issue is that there does not seem to be a NET method named SHA2. The closest I could find is SHA512 and I am not sure if SHA512 is a .NET implementation of SHA2.
Secondly, padding for AES has been specified as PKCS5Padding but again the closest (naming-wise) I could find is PKCS7 which I am not sure about how similar it is to PKCS5.
There is also the matter of an Initialisation Vector (IV), which the AES parameters don't specify but I see C# AES examples including. In the code, I have set it to have the same value as the Key (which I believe
is what the API calls "secret key") out of sheer desperation but I have tried making the request without setting IV to any value and still get back a 401.
I should probably also mention that I am using ASCII encoding to convert to-and-from bytes because I first tried using UTF8 but when it came to actually making the HTTP request, I was getting an exception
saying that header values (remember we are generating an authorisation key that will be tucked in a HTTP request header) should only be encoded in ASCII.
Any help pointing me in the right direction will be immensely appreciated as I am woefully out of my depth with this cryptography stuff.

Don't worry, crypto can feel overwhelmingly complicated. I think you're close.
SHA2 is a family of hash functions. In practice, "SHA2" usually means SHA2-256 or occasionally SHA2-512. My guess is that your external API is probably using the more common SHA2-256.
This answer on crypto.stackexchange explains that PKCS#5 is essentially a subset of PKCS#7. I'd be willing to bet that the API you're calling made the same mistake described in that answer and should really be calling it PKCS7Padding. Your code is fine!
The IV isn't the same thing as the secret key (or just the "key" for AES). The IV should be random for every encryption run. You aren't supposed to derive it from the input plaintext or the input key. Fortunately, AesCryptoServiceProvider.GenerateIV() will generate one for you. It's up to you to prepend it to your output stream, though.
Using Encoding.ASCII.GetBytes() to get the plaintext and secret key bytes makes sense to me. I don't think that's causing a problem.
Stealing from this excellent answer to a similar question (go give them a vote!), I'd try code like this:
static byte[] AesEncrypt(byte[] data, byte[] key)
{
if (data == null || data.Length <= 0)
{
throw new ArgumentNullException($"{nameof(data)} cannot be empty");
}
if (key == null || key.Length != AesKeySize)
{
throw new ArgumentException($"{nameof(key)} must be length of {AesKeySize}");
}
using (var aes = new AesCryptoServiceProvider
{
Key = key,
Mode = CipherMode.CBC,
Padding = PaddingMode.PKCS7
})
{
aes.GenerateIV();
var iv = aes.IV;
using (var encrypter = aes.CreateEncryptor(aes.Key, iv))
using (var cipherStream = new MemoryStream())
{
using (var tCryptoStream = new CryptoStream(cipherStream, encrypter, CryptoStreamMode.Write))
using (var tBinaryWriter = new BinaryWriter(tCryptoStream))
{
// prepend IV to data
cipherStream.Write(iv);
tBinaryWriter.Write(data);
tCryptoStream.FlushFinalBlock();
}
var cipherBytes = cipherStream.ToArray();
return cipherBytes;
}
}
}
Unless there's something else weird going on with this API, I'd guess it's probably #3 above that is causing your request to fail.

I finally managed to get it to work.
A big part of the problem was that API documentation did not specify that hashedString has to
be composed of hexadecimal characters.
It also didn't say that authKey should be a base64 string.
I don't know if this is so standard that it goes without saying but knowing this could have
saved me hours of agony. I was converting the hashed/encrypted bytes back to ASCII
and much of it was unprintable characters that were causing the server to send back
a HTTP response with status 400 BAD_REQUEST.
It also required hashedString to be hashed using SHA256 but the documentation does not mention it.
Thanks to #Nate Barbettini's answer for steering me in the right direction on this.
Also, it appears that AES ECB mode does not require an initialisation vector unlike other
modes like CBC so I didn't specify an IV.
For padding I specified PKCS7 (again thanks to #Nate Barbettini for that).
With that here's the code that finally worked out for me.
string hashedFields = ComputeSha256HashHex(authToken + password + devId);
string encryptedString = AesEncryptToBase64String(saltString + orgId + "=" + hashedFields, secretKey);
private string AesEncryptToBase64String(string plainText, string key)
{
// Convert string arguments into byte arrays
byte[] keyBytes = Encoding.ASCII.GetBytes(key);
byte[] plainTextBytes = Encoding.ASCII.GetBytes(plainText);
// Check arguments.
if (plainText == null || plainText.Length <= 0)
throw new ArgumentNullException("plainText");
if (key == null || key.Length <= 0)
throw new ArgumentNullException("key");
byte[] encrypted;
// Create an Aes object
// with the specified key and IV.
using (Aes aesAlg = Aes.Create())
{
aesAlg.Key = keyBytes;
aesAlg.Padding = PaddingMode.PKCS7;
aesAlg.Mode = CipherMode.ECB;
// Create an encryptor to perform the stream transform.
ICryptoTransform encryptor = aesAlg.CreateEncryptor();
// Create the streams used for encryption.
using (MemoryStream msEncrypt = new MemoryStream())
{
using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
{
using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
{
//Write all data to the stream.
swEncrypt.Write(plainText);
}
encrypted = msEncrypt.ToArray();
}
}
}
// Return encrypted bytes as Base 64 string
return Convert.ToBase64String(encrypted);
}
private string ComputeSha256HashHex(string plainText)
{
using (SHA256 sha256Hash = SHA256.Create())
{
// ComputeHash - returns byte array
byte[] bytes = sha256Hash.ComputeHash(Encoding.UTF8.GetBytes(plainText));
// Convert byte array to a string
return BytesToHexString(bytes);
}
}
private string BytesToHexString(byte[] bytes)
{
// Convert byte array to a string
StringBuilder builder = new StringBuilder();
for (int i = 0; i < bytes.Length; i++)
{
builder.Append(bytes[i].ToString("x2"));
}
return builder.ToString();
}

C# AES encryption performs only once

I have a C# WinForms app, with AES encryption/decryption. The encryption (decryption) itself works fine, but only once. If I try to encrypt another string, I get a CryptographyException saying the padding is invalid. Based on some research, it seems I forgot to close some stream, but I can't figure out what it is. Does anyone know how to fix this?
Here is the code I use (I believe I found it earlier somewher on SO):
static string DecryptStringFromBytes_Aes(byte[] cipherText, byte[] Key
, byte[] IV)
{
// Check arguments.
if (cipherText == null || cipherText.Length <= 0)
throw new ArgumentNullException("cipherText");
if (Key == null || Key.Length <= 0)
throw new ArgumentNullException("Key");
if (IV == null || IV.Length <= 0)
throw new ArgumentNullException("Key");
// Declare the string used to hold
// the decrypted text.
string plaintext = null;
// Create an Aes object
// with the specified key and IV.
using (Aes aesAlg = Aes.Create())
{
aesAlg.Padding = PaddingMode.PKCS7;
aesAlg.Key = Key;
aesAlg.IV = IV;
// Create a decrytor to perform the stream transform.
ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key
, aesAlg.IV);
// Create the streams used for decryption.
using (MemoryStream msDecrypt = new MemoryStream(cipherText))
{
using (CryptoStream csDecrypt = new CryptoStream(msDecrypt
, decryptor, CryptoStreamMode.Read))
{
using (StreamReader srDecrypt = new StreamReader(
csDecrypt))
{
// Read the decrypted bytes from the decrypting stream
// and place them in a string.
//csDecrypt.FlushFinalBlock(); causes an exception
plaintext = srDecrypt.ReadToEnd();
//csDecrypt.Flush(); experimental solution, doesn't work either
srDecrypt.Close();
}
csDecrypt.Close();
}
msDecrypt.Close();
}
}
return plaintext;
}
static byte[] EncryptStringToBytes_Aes(string plainText, byte[] Key,
byte[] IV)
{
// Check arguments.
if (plainText == null || plainText.Length <= 0)
throw new ArgumentNullException("plainText");
if (Key == null || Key.Length <= 0)
throw new ArgumentNullException("Key");
if (IV == null || IV.Length <= 0)
throw new ArgumentNullException("Key");
byte[] encrypted;
// Create an Aes object
// with the specified key and IV.
using (Aes aesAlg = Aes.Create())
{
aesAlg.Padding = PaddingMode.PKCS7;
aesAlg.Key = Key;
aesAlg.IV = IV;
// Create a decrytor to perform the stream transform.
ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key
, aesAlg.IV);
// Create the streams used for encryption.
using (MemoryStream msEncrypt = new MemoryStream())
{
using (CryptoStream csEncrypt = new CryptoStream(msEncrypt
, encryptor, CryptoStreamMode.Write))
{
using (StreamWriter swEncrypt = new StreamWriter(
csEncrypt))
{
//Write all data to the stream.
swEncrypt.Write(plainText);
swEncrypt.Close();
}
csEncrypt.Close();
msEncrypt.Close();
encrypted = msEncrypt.ToArray();
//csEncrypt.FlushFinalBlock(); causes an exception saying it was already called
}
}
}
Here is a sample of code I use to test the ecnryption. Performs correctly, but only once...
The key and IV are converted into Unicode string so that the user is able to save it and use it later for decryption.
private void button7_Click(object sender, EventArgs e)
{
string aesKey = "";
string aesIV = "";
string ciphered = "";
string deciphered = "";
using (Aes myAes = Aes.Create())
{
myAes.GenerateKey();
myAes.GenerateIV();
aesKey = Encoding.Unicode.GetString(myAes.Key);
aesIV = Encoding.Unicode.GetString(myAes.IV);
ciphered = Encoding.Unicode.GetString(EncryptStringToBytes_Aes(".ahoj.", myAes.Key, myAes.IV));
byte[] deKey = Encoding.Unicode.GetBytes(aesKey);
byte[] deIv = Encoding.Unicode.GetBytes(aesIV);
deciphered = DecryptStringFromBytes_Aes(Encoding.Unicode.GetBytes(ciphered), deKey, deIv);
MessageBox.Show("key: " + aesKey + "\niv: " + aesIV + "\ndekey: " + Encoding.Unicode.GetString(deKey) + "\ndeIv: " + Encoding.Unicode.GetString(deIv) + "\nDeciphered: " + deciphered);
}
}

Instead of using GetBytes and GetString from the unicode encoding, I would recommend base 64 encoding the bytes.
You can do base 64 encoding using Convert.ToBase64String() and Convert.FromBase64String.
One problem with just getting the unicode string from a generated byte array is that there is no guarantee that all of the characters are printable characters. For example, if you have a 0 in the byte array, that will be a null control character.

I recently ran into this myself. I am making use of the 'using' statements in your first code block but I never call .Close() and I am not running into the issue of only being able to run once.
To solve issues with padding on decrypt and issue of non-printable characters, I am explicitly setting the Padding as you did in the first code block but I am using Encoding.Default.GetBytes(cipherText); and the GetString method of the same encoding so it uses Window's default Extended ASCII encoding so it will recognize all the characters.

decrpyt .Net Encrypted string in iOS

I made some AES encryption in c# and works like a charm. Code here:
public string EncryptStringAES(string plainText, string sharedSecret)
{
if (string.IsNullOrEmpty(plainText))
throw new ArgumentNullException("plainText");
if (string.IsNullOrEmpty(sharedSecret))
throw new ArgumentNullException("sharedSecret");
string outStr = null; // Encrypted string to return
RijndaelManaged aesAlg = null; // RijndaelManaged object used to encrypt the data.
try
{
_pkey = sharedSecret;
// generate the key from the shared secret and the salt
Rfc2898DeriveBytes key = new Rfc2898DeriveBytes(sharedSecret, _salt);
//_key = key.ToString();
// Create a RijndaelManaged object
aesAlg = new RijndaelManaged();
aesAlg.Key = key.GetBytes(aesAlg.KeySize / 8);
_key = Encoding.ASCII.GetString(aesAlg.Key);
// Create a decryptor to perform the stream transform.
ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);
// Create the streams used for encryption.
using (MemoryStream msEncrypt = new MemoryStream())
{
// prepend the IV
msEncrypt.Write(BitConverter.GetBytes(aesAlg.IV.Length), 0, sizeof(int));
msEncrypt.Write(aesAlg.IV, 0, aesAlg.IV.Length);
using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
{
using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
{
//Write all data to the stream.
swEncrypt.Write(plainText);
}
}
outStr = Convert.ToBase64String(msEncrypt.ToArray());
}
}
finally
{
// Clear the RijndaelManaged object.
if (aesAlg != null)
aesAlg.Clear();
}
// Return the encrypted bytes from the memory stream.
return outStr;
}
/// <summary>
/// Decrypt the given string. Assumes the string was encrypted using
/// EncryptStringAES(), using an identical sharedSecret.
/// </summary>
/// <param name="cipherText">The text to decrypt.</param>
/// <param name="sharedSecret">A password used to generate a key for decryption.</param>
public string DecryptStringAES(string cipherText, string sharedSecret)
{
if (string.IsNullOrEmpty(cipherText))
throw new ArgumentNullException("cipherText");
if (string.IsNullOrEmpty(sharedSecret))
throw new ArgumentNullException("sharedSecret");
// Declare the RijndaelManaged object
// used to decrypt the data.
RijndaelManaged aesAlg = null;
// Declare the string used to hold
// the decrypted text.
string plaintext = null;
try
{
_pkey = sharedSecret;
// generate the key from the shared secret and the salt
Rfc2898DeriveBytes key = new Rfc2898DeriveBytes(sharedSecret, _salt);
//_key = key.ToString();
// Create the streams used for decryption.
byte[] bytes = Convert.FromBase64String(cipherText);
using (MemoryStream msDecrypt = new MemoryStream(bytes))
{
// Create a RijndaelManaged object
// with the specified key and IV.
aesAlg = new RijndaelManaged();
aesAlg.Key = key.GetBytes(aesAlg.KeySize / 8);
_key = Encoding.ASCII.GetString(aesAlg.Key);
// Get the initialization vector from the encrypted stream
aesAlg.IV = ReadByteArray(msDecrypt);
// Create a decrytor to perform the stream transform.
ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
{
using (StreamReader srDecrypt = new StreamReader(csDecrypt))
// Read the decrypted bytes from the decrypting stream
// and place them in a string.
plaintext = srDecrypt.ReadToEnd();
}
}
}
finally
{
// Clear the RijndaelManaged object.
if (aesAlg != null)
aesAlg.Clear();
}
return plaintext;
}
NOTE:
I am encryting a fair amout of data here(large json string)
Now the next step would be to make the same magic with iOS here is the problem that I am a newb when it comes to IOS and I am hoping someone can point me in the right direction.
Problems:
I so far failed to find an example on iOS how to make Rfc289 key with secret and salt key
I tryed this example the trick here is that the c# code does not work with large strings it only works with short strings.
Basicly I would like some suggestions or mybe some other aproach to make secure communication between rest api Web Service Application and iOS.
Thank you for help.

Add an SSL certificate to your WebAPI end point - then use fully secure communications endpoint to endpoint, you should not code anything except change http:// to https://

Hexadecimal Characters in Encoded XML Attribute

I'm using following method to encrypt the data before storing them into database. The data will be converted to XML upon retrieval and passed to data-access layer to be deserialized into a known business entity object.
The problem is there are some Hexadecimal characters in data due to encoding and that makes the xml an invalid xml document so it can't be deserialized.
How should I solve this problem?
public static string EncryptStringAES(string plainText, string sharedSecret)
{
if (string.IsNullOrEmpty(plainText))
throw new ArgumentNullException("plainText");
if (string.IsNullOrEmpty(sharedSecret))
throw new ArgumentNullException("sharedSecret");
string outStr = null; // Encrypted string to return
RijndaelManaged aesAlg = null; // RijndaelManaged object used to encrypt the data.
try
{
// generate the key from the shared secret and the salt
Rfc2898DeriveBytes key = new Rfc2898DeriveBytes(sharedSecret, _salt);
// Create a RijndaelManaged object
aesAlg = new RijndaelManaged();
aesAlg.Key = key.GetBytes(aesAlg.KeySize / 8);
// Create a decryptor to perform the stream transform.
ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);
// Create the streams used for encryption.
using (MemoryStream msEncrypt = new MemoryStream())
{
// prepend the IV
msEncrypt.Write(BitConverter.GetBytes(aesAlg.IV.Length), 0, sizeof(int));
msEncrypt.Write(aesAlg.IV, 0, aesAlg.IV.Length);
using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
{
using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
{
//Write all data to the stream.
swEncrypt.Write(plainText);
}
}
outStr = Convert.ToBase64String(msEncrypt.ToArray());
}
}
finally
{
// Clear the RijndaelManaged object.
if (aesAlg != null)
aesAlg.Clear();
}
// Return the encrypted bytes from the memory stream.
return outStr;
}

I usually use HttpUtility.HtmlEncode to escape values for XML.

AES_DECRYPT() and AES_ENCRYPT() in MySQL with Polish characters

I have a MySQL database which is configured to receive a data with polish characters (f. ex ą, ę, ó, ł, ń etc.).
Now I want to send data with these Polish characters to a db using AES_ENCRYPT(), and then get them from there using AES_DECRYPT().
My problem is that I receive a byte[] array in C# which has X elements where X is length of text I receive. And every single array element has an ASCII code of an character it represents. I could easily convert it to text using Encoding Class, but I won't get Polish characters in output text.
F. ex.:
I send AES_ENCRYPT('ąąą', '123') to db.
I get AES_DECRYPT('sql command','123') and I get byte[] which has 3 elements, everyone with '97' value which represents 'aaa' - NOT 'ąąą'.
How to use AES_DECRYPT/ENCRYPT in a way which allows me to send/get polish characters to my DB?!
Or how to get string output from aes_decrypt() instead byte[]?

convert using encoding might help you.
select convert(aes_decrypt(aes_encrypt('ąąą', 'abcdefg'), 'abcdefg') using UTF8);

Why don't you just implement encryption/decryption in code instead of in queries?
private static Byte[] Encrypt(String toEncrypt, Byte[] Key, Byte[] IV)
{
CryptoStream streamCrypto = null;
MemoryStream streamMemory = null;
RijndaelManaged aes = null;
StreamWriter streamWriter = null;
try
{
aes = new RijndaelManaged();
aes.Key = Key;
aes.IV = IV;
ICryptoTransform encryptor = aes.CreateEncryptor(aes.Key, aes.IV);
streamMemory = new MemoryStream();
streamCrypto = new CryptoStream(streamMemory, encryptor, CryptoStreamMode.Write);
streamWriter = new StreamWriter(streamCrypto);
streamWriter.Write(toEncrypt);
}
finally
{
if (streamWriter != null)
streamWriter.Close();
if (streamCrypto != null)
streamCrypto.Close();
if (streamMemory != null)
streamMemory.Close();
if (aes != null)
aes.Clear();
}
return streamMemory.ToArray();
}
public static String Decrypt(Byte[] toDecrypt, Byte[] Key, Byte[] IV)
{
CryptoStream streamCrypto = null;
MemoryStream streamMemory = null;
RijndaelManaged aes = null;
StreamReader streamReader = null;
String output = null;
try
{
aes = new RijndaelManaged();
aes.Key = Key;
aes.IV = IV;
ICryptoTransform decryptor = aes.CreateDecryptor(aes.Key, aes.IV);
streamMemory = new MemoryStream(toDecrypt);
streamCrypto = new CryptoStream(streamMemory, decryptor, CryptoStreamMode.Read);
streamReader = new StreamReader(streamCrypto);
output = streamReader.ReadToEnd();
}
finally
{
if (streamReader != null)
streamReader.Close();
if (streamCrypto != null)
streamCrypto.Close();
if (streamMemory != null)
streamMemory.Close();
if (aes != null)
aes.Clear();
}
return output;
}
In your code, you encrypt your string and then you send encrypted data to the database:
Byte[] encrypted = Encrypt(yourString, Key, IV);
When you pull out data from the database, you just get back your string using:
String decrypted = Decrypt(dbData, Key, IV);
If you don't like this way, just use your queries like so:
INSERT INTO mysecrets (mysecret1, mysecret2) VALUES (AES_ENCRYPT(secret1, YOUR_ENCRYPTION_KEY), AES_ENCRYPT(secret2, YOUR_ENCRYPTION_KEY))
SELECT AES_DECRYPT(mysecret1, YOUR_ENCRYPTION_KEY) AS secret1, AES_DECRYPT(mysecret1, YOUR_ENCRYPTION_KEY) AS secret2 FROM mysecrets

Your MySQL data is in characters, while encryption works on bytes. You need to convert your characters to bytes before encrypting them, and also convert the decrypted bytes back to characters. That means you need to explicitly specify the character encoding to be used at both ends so they match. The current standard is UTF-8, so you should specify that at each end. If UTF-8 does not work, then try some Microsoft specific character encoding at both ends.