RSA+AES Cryptor

RSA+AES Encryption/Decryption library for iOS. This library uses 2048-bit RSA and 256-bit key with 128-bit block size AES for encryption/decryption.

Encryption

Load public key from X509 Certificate file (DER format), encrypt NSData using AES algorithm with generated Key and IV, returns encrypted NSData with format below.

| AES IV | encrypted AES Key | AES encrypted data |
|  0-15  |       16-271      |        272-n       |

Sample code:

NSString *pubKeyPath = [[NSBundle mainBundle] pathForResource:@"publicKey" ofType:@"cer"];

RSAESCryptor *cryptor = [RSAESCryptor sharedCryptor];
[cryptor loadPublicKey:pubKeyPath];
NSData *encData = [cryptor encryptData:plainData];

// encrypted data format:
// [16 bytes IV] + [256 bytes encrypted Key] + [AES encrypted data].

Decryption

Load private key from PKCS#12/PFX format file, decrypt NSData according to the format described above.

NSString *priKeyPath = [[NSBundle mainBundle] pathForResource:@"privateKey" ofType:@"p12"];

RSAESCryptor *cryptor = [RSAESCryptor sharedCryptor];
[cryptor loadPrivateKey:priKeyPath password:password];
NSData *decData = [cryptor decryptData:encData];

How to create .cer and .p12 in Windows

1. Open Visual Studio Command Prompt
2. C:\> makecert -pe -ss My -sr LocalMachine -n CN="YOUR_CERT_NAME" -sky exchange -len 2048
3. C:\> mmc
4. Add Certificates snap-in in MMC console, choose computer accounts
5. expand Personal/Certificate folder, then export which you want.

How to decrypt using C# (File-based cert)

// get cert from pfx file.
var pfxFileName = @"C:\privateKey.p12";
var password = @"PFX_PASSWORD";
var cert = new X509Certificate2(pfxFileName, password);

var rsa = (RSACryptoServiceProvider)cert.PrivateKey;
byte[] data = SomeClass.GetRSAESCryptorEncryptedByteArray();

var iv = data.Take(16).ToArray();
var encSymKey = data.Skip(16).Take(256).ToArray();
var encData = data.Skip(16 + 256).ToArray();

var symKey = rsa.Decrypt(encSymKey, false);

var aes = AesManaged.Create();
using (var inStream = new CryptoStream(new MemoryStream(encData), aes.CreateDecryptor(symKey, iv), CryptoStreamMode.Read))
{
	// read data from inStream
}

How to get cert from Certificate Store in Windows

// get cert from X.509 store of local machine
var store = new X509Store(StoreLocation.LocalMachine);
store.Open(OpenFlags.ReadOnly);
var cert = store.Certificates.Cast<X509Certificate2>()
			.FirstOrDefault(c => c.Subject == "CN=YOUR_CERT_NAME");
store.Close();