Develop Reference

Encoding problem in C# decrypting in bouncycastle from openssl

I'm trying to decrypt in c#, using bouncycastle, the result of the following php code:
<?php
$plaintext = 'The quick brown fox jumps over the lazy dog';
$cipher = "AES-128-CTR";
$key = "F5UgsDQddWGdgjddJtNgg6xE3V9uwaCR";
if (in_array($cipher, openssl_get_cipher_methods()))
{
$ivlen = openssl_cipher_iv_length($cipher);
$iv = '2782614358578542';
$ciphertext = openssl_encrypt($plaintext, $cipher, $key, $options=0, $iv, $tag);
echo $ciphertext."\n";
}
?>
My c# code is as follows:
public string Decrypt(string toDecrypt, string keyStr, string ivStr)
{
byte[] inputBytes = Convert.FromBase64String(toDecrypt);
byte[] keyBytes = Encoding.UTF8.GetBytes(keyStr);
byte[] iv = Encoding.UTF8.GetBytes(ivStr);
IBufferedCipher cipher = CipherUtilities.GetCipher("AES/CTR/PKCS7PADDING");
cipher.Init(false, new ParametersWithIV(ParameterUtilities.CreateKeyParameter("AES", keyBytes), iv));
byte[] decryptedBytes = cipher.DoFinal(inputBytes);
return Encoding.UTF8.GetString(decryptedBytes);
}
The php code returns
7/q61uOzeC4iycFIMrjvh01zvjOuCtnX8eWob8MAA5kIfMOIx915ctBIyw==
But when I make in C# the following call
Decrypt("7/q61uOzeC4iycFIMrjvh01zvjOuCtnX8eWob8MAA5kIfMOIx915ctBIyw==", "F5UgsDQddWGdgjddJtNgg6xE3V9uwaCR", "2782614358578542");
I get the following gibberish:
���yF�l����c:�-��7K�(�,�X�.[�W"�ܜ��J�
Which makes me think that I'm missing or doing something wrong with the encoding but I can't seem to figure it out.

AES-128 uses a 16 bytes key. In the PHP code, however, a 32 bytes key is used, which PHP implicitly truncates by considering only the first 16 bytes.
So the fix is to shorten the key in the C# code accordingly, i.e. use F5UgsDQddWGdgjdd.
Alternatively, change the AES variant in the PHP code to AES-256 (aes-256-ctr), which results in the ciphertext Tw05j9QDfaBK7zbyt9jine8xWqnzNB2Pim7rtv7gDba2TsE7ejvvjP5YKA==.
Additionally, in the C# code, apply AES/CTR/NoPadding, since CTR is a stream cipher mode that does not require padding, which is why padding is implicitly disabled in the PHP code.
Note that for security reasons, key/IV pairs must not be reused, especially for CTR. Therefore, for a fixed key, a static IV must not be applied, but a random one (which is passed to the decrypting side together with the ciphertext, usually concatenated).

AES128-ECB under UWP

I need help in retrieving AES128-EBC encrypted string under Universal Windows Application.
I have a password in string that is used as a key. With it's 32 bits length MD5 hash value I would like to encrypt text with AES128-EBC.
Now I am using this for creating MD5Hash:
public string GetMD5Hash(String strMsg)
{
string strAlgName = HashAlgorithmNames.Md5;
IBuffer buffUtf8Msg = CryptographicBuffer.ConvertStringToBinary(strMsg, BinaryStringEncoding.Utf8);
HashAlgorithmProvider objAlgProv = HashAlgorithmProvider.OpenAlgorithm
string strAlgNameUsed = objAlgProv.AlgorithmName;
IBuffer buffHash = objAlgProv.HashData(buffUtf8Msg);
if (buffHash.Length != objAlgProv.HashLength)
{
throw new Exception("There was an error creating the hash");
}
string hex = CryptographicBuffer.EncodeToHexString(buffHash);
return hex;
}
And this code for encryption:
public string Encrypt(string input, string pass)
{
SymmetricKeyAlgorithmProvider provider = SymmetricKeyAlgorithmProvider.OpenAlgorithm(SymmetricAlgorithmNames.AesEcbPkcs7);
CryptographicKey key;
string encrypted = "";
byte[] keyhash = Encoding.ASCII.GetBytes(GetMD5Hash(pass));
key = provider.CreateSymmetricKey(CryptographicBuffer.CreateFromByteArray(keyhash));
IBuffer data = CryptographicBuffer.CreateFromByteArray(Encoding.Unicode.GetBytes(input));
encrypted = CryptographicBuffer.EncodeToBase64String(CryptographicEngine.Encrypt(key, data, null));
return encrypted;
}
The cause why I am using SymmetricAlgorithmNames.AesEcbPkcs7 is when I am using SymmetricAlgorithmNames.AesEcb the output string is empty. I don't understand why.
My question is: Does my code create an AES128-ECB encryption? Because I not really sure it does. Because the software that is waiting for that encrypted data not recognizes it, so it cannot decrypt it.

My question is: Does my code create an AES128-ECB encryption? Because I not really sure it does. Because the software that is waiting for that encrypted data not recognizes it, so it cannot decrypt it.
Yes, your code create an AES encryption with ECB cipher mode and PKCS7 padding. If I correctly understand your problem, you said this works with AesEcbPkcs7, but failed using AesEcb, your software for decryption doesn't work for this.
The difference between AesEcbPkcs7 and AesEcb is, AesEcbPkcs7 use PKCS#7 block padding modes, and PKCS #7 algorithms automatically pads the message to an appropriate length, so you don’t need to pad the cipher to a multiple of the block-size of the algorithm you are using. So if you insist to use AesEcb to encrypt, I recommend to use `AesEcbPkcs7, otherwise an exception: The supplied user buffer is not valid for the requested operation.
So I guess, one possibility here in your decryption software, it may have the ability to use AesEcbPkcs7, but it doesn't implement the decrytion of AesEcb. Here I tested decryption based on your code, this code can decrypt AesEcb correctly:
public string Decrypt(string input, string pass)
{
var keyHash = Encoding.ASCII.GetBytes(GetMD5Hash(pass));
// Create a buffer that contains the encoded message to be decrypted.
IBuffer toDecryptBuffer = CryptographicBuffer.DecodeFromBase64String(input);
// Open a symmetric algorithm provider for the specified algorithm.
SymmetricKeyAlgorithmProvider aes = SymmetricKeyAlgorithmProvider.OpenAlgorithm(SymmetricAlgorithmNames.AesEcb);
// Create a symmetric key.
var symetricKey = aes.CreateSymmetricKey(keyHash.AsBuffer());
var buffDecrypted = CryptographicEngine.Decrypt(symetricKey, toDecryptBuffer, null);
string strDecrypted = CryptographicBuffer.ConvertBinaryToString(BinaryStringEncoding.Utf8, buffDecrypted);
return strDecrypted;
}
Another possibility I think you catch the exception when using AesEcb and the user buffer is not valid for the requested operation and handled it when you call your Encrypt(string input, string pass) method, the encryption failed actually.

String encryption in Objective-C decrypt in C#

I am building a iPhone app which uses a c# web service. My iPhone app takes in some data and encrypts it and passes it to the web service. How do I decrypt the data in C#?
My iPhone app contains the following code:
NSString *pString = #"Some string to be encoded";
NSString *key = #"My encryption key";
NSData *pData = [pString dataUsingEncoding:NSUTF8StringEncoding];
pData = [pData AES256EncryptWithKey:key];
NSString *pID = [pData base64EncodedStringWithOptions:NSDataBase64Encoding76CharacterLineLength];
EDIT: The data is already stored in the web service so I can't readily change the encryption approach. The C# application is not on the server so there is no possibility of compromising the key.
I have tried the following C# code to decrypt the data:
static string DecryptString(string encryptedText, string key)
{
byte[] encryptedString = Convert.FromBase64String(encryptedText);
byte[] encryptionKey = Encoding.UTF8.GetBytes(key.Substring(0, 32));
using (var provider = new AesCryptoServiceProvider())
{
provider.Mode = CipherMode.CBC;
provider.Padding = PaddingMode.PKCS7;
provider.Key = encryptionKey;
using (var ms = new MemoryStream(encryptedString))
{
// Read the first 16 bytes which is the IV.
byte[] iv = new byte[16];
ms.Read(iv, 0, 16);
provider.IV = iv;
using (var decryptor = provider.CreateDecryptor())
{
using (var cs = new CryptoStream(ms, decryptor, CryptoStreamMode.Read))
{
using (var sr = new StreamReader(cs))
{
return sr.ReadToEnd();
}
}
}
}
}
}
However, I get the following exception:
System.Security.Cryptography.CryptographicException was unhandled
HResult=-2146233296 Message=Padding is invalid and cannot be
removed.
The encryptedText received by DecryptString is 80 bytes in length.

The sample ObjC code uses by default CBC modem, PKCS#7 padding and a default iv of 16 0x00 bytes.
The C# also uses CBC mode and PKCS#7 padding. The decryption code expects a 16-byte iv pre-pended to the encrypted data and that does not exist.
byte[] iv = new byte[16];
ms.Read(iv, 0, 16);
provider.IV = iv;
This needs to be changed so that iv is set to an array of 16 0x00 bytes and the ms.Read(iv, 0, 16) statement needs to be deleted so the decrypt function gets all of the encrypted data.
Notes:
Using a devault anything in encryption is a bad idea, always provide the correect length data.
Authentication of the encrypted data needs should be added so that it can be determined if there an incorrect key or the data has been tampered with.
There really should be a version number and a random IV used and prepended to the encrypted so you should really consider correcting this. This demonstrates why a version number generally needs to be provided and used.
RNCryptor covers the above issues.
The handling of the encryption key also needs to be considered so that is is as secure as necessary.

You need to first decode the base-64 encoded string to a byte[] - see Convert.FromBase64String(). Then you need to use the Aes class to decrypt it - there's an example on its documentation page.

Data encrypted in C# is 1 byte too long to be decrypted in Java

I have a server written in Java which sends converts its RSA key to the XML format used by .NET before sending it to the client:
public String getPublicKeyXML() {
try {
KeyFactory factory = KeyFactory.getInstance("RSA");
RSAPublicKeySpec publicKey = factory.getKeySpec(this.keyPair.getPublic(), RSAPublicKeySpec.class);
byte[] modulus = publicKey.getModulus().toByteArray();
byte[] exponent = publicKey.getPublicExponent().toByteArray();
String modulusStr = Base64.encodeBytes(modulus);
String exponentStr = Base64.encodeBytes(exponent);
String format =
"<RSAKeyValue>" +
"<Modulus>%s</Modulus>" +
"<Exponent>%s</Exponent>" +
"</RSAKeyValue>";
return String.format(format, modulusStr, exponentStr);
} catch (Exception e) {
this.server.logException(e);
return "";
}
}
The client, written in C#, then loads the key and uses it to encrypt a 256 bit AES key:
public static byte[] encrypt(string xmlKey, byte[] bytes)
{
RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
rsa.FromXmlString(xmlKey);
byte[] cipherBytes = rsa.Encrypt(bytes, false);
rsa.Clear();
return cipherBytes;
}
The server is then supposed to decrypt the AES key using its private RSA key:
public byte[] decrypt(byte[] data) {
try {
PrivateKey privateKey = this.keyPair.getPrivate();
Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
cipher.init(Cipher.DECRYPT_MODE, privateKey);
byte[] cipherData = cipher.doFinal(data);
return cipherData;
} catch (Exception e) {
this.server.logException(e);
return new byte[0];
}
}
However, the server fails with an error stating "Data must not be longer than 384 bytes." Looking at the data to be decrypted, I noticed that it's 385 bytes. I tried increasing the RSA key length, and now the server tells me the data must be no longer than 512 bytes, while the encrypted data from the client is 513 bytes. Why is the encrypted data always one byte longer than expected?
EDIT:
Here's a sample XML-formatted key as is transmitted from the server to the client:
<RSAKeyValue><Modulus>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</Modulus><Exponent>AQAB</Exponent></RSAKeyValue>
I have verified that the data sent is the same as the data being received.
Knocking off the last byte results in a BadPaddingException. I also tried knocking off the first byte, with the same result.

I found the problem. The BigInteger's toByteArray() function included a leading zero for some reason. I just removed the leading zeros from the array and it now works like a charm!

This will not fix the problem (I tested it to no avail), but I wanted to call to your attention that RSACryptoServiceProvider implements the IDisposable interface and therefore should be properly disposed of when complete. Your C# encrypt method can be written a bit better (and more concise!) as such:
public static byte[] encrypt(string xmlKey, byte[] bytes)
{
using (var rsa = new RSACryptoServiceProvider())
{
rsa.FromXmlString(xmlKey);
return rsa.Encrypt(bytes, false);
}
}

How to use c# to decrypt an MD5 hash that is encrypted using RSA1024

I trying to verify the integrity of a file at work and an having a hard time of it. I'm not very well versed with encryption and hashing, so bear with me.
I have some files that have an MD5 hash located at the end of them. I have written code to grab the bytes that I think are the hash and they seen to be uniformly 128 bytes long. In the file, just before the hash, is the keyword "RSA1024", which I have taken to mean the hash is encrypted using RSA 1024.
I have what I know is the RSA key in a file, and have read out the bytes (always 258 bytes long). I have seen many tutorials which use FromXmlString() to pull in the key, but this RSA key was not generated using the .net framework, and is not in an XML format.
I have written the following method to decrypt the hash data using the key, and it throws this error when executing ImportCspBlob() - System.Security.Cryptography.CryptographicException: Bad Version of provider.
Any ideas?
public byte[] DecryptRSA(byte[] encryptedData, byte[] keyData)
{
CspParameters param = new CspParameters();
param.Flags = CspProviderFlags.UseExistingKey;
RSACryptoServiceProvider rsaProvider = new RSACryptoServiceProvider(param);
rsaProvider.ImportCspBlob(keyData);
byte[] decryptedData = rsaProvider.Decrypt(encryptedData, false);
return decryptedData;
}
Basic Algorithm
It may sound strange to want to "decrypt an MD5 hash", and especially when one says that they want to "decrypt it with a public key". But that is how digital signatures work. With RSA you can:
encrypt with private key
decrypt with the public key
The message digest is encrypted with the private key, and can then only be decrypted with the public key. That way you know that only the person with the private key could have signed the message.

Your key is most likely not a CSP-type key (it is most likely DER encoded). You can decrypt it using Bouncy Castle with the DER key like this:
RsaPrivateCrtKeyParameters privateKey = (RsaPrivateCrtKeyParameters)PrivateKeyFactory.CreateKey(key);
byte[] rv = null;
RsaEngine eng = new RsaEngine();
eng.Init(false, privateKey);
int size = eng.GetOutputBlockSize();
rv = eng.ProcessBlock(cipher, 0, cipher.Length);
EDIT: to addressing GregS scenario that it may be a signature verify operation
If you are trying to verify a signature, you would need a certificate used to verify a message, the original message text, and the existing message signature to compare against.
What you do is pass in the original message text (minus the signature), the bytes of the message signature, and the path to the certificate you will use to verify the passed in signature.
Then, you will hash the original message and compare the result against the passed in signature.
Here is some code to illustrate:
private bool VerifySignature(string messageText, byte[] messageSignature, string certificatePath)
{
// Load the certificate from a file
X509Certificate2 cert = new X509Certificate2(certificatePath);
// Get public key
RSACryptoServiceProvider csp = (RSACryptoServiceProvider)cert.PublicKey.Key;
// Next, hash the messageText
SHA1Managed sha1 = new SHA1Managed();
byte[] messageBytes = Encoding.Unicode.GetBytes(messageText);
byte[] hash = sha1.ComputeHash(messageBytes);
// Verify the signature with the hash
return csp.VerifyHash(hash, CryptoConfig.MapNameToOID("SHA1"), messageSignature);
}

MD5 is one-way hash. But you might check out hashing algorithm. There are some ways to break this hash, just do some research ;)