Issue using CCCrypt (CommonCrypt) in Swift
I am porting a working Objective-C Category (NSData+AESCrypt.m) to Swift and I have found an issue working with the pointers. The code for the encrypting part in Swift compiles correctly, but generates a runtime EXEC_BAD_ACCES error.
The code I have so far is (I tried to dissect the code as much as possible) :
let key = "123456789012345678901234567890120"
let keyLength = UInt(kCCKeySizeAES256 + 1)
let keyPointer = strdup(key) // Convert key to <UnsafeMutablePointer<Int8>
let message = "Don´t try to read this text. Top Secret Stuff"
let data = (message as NSString).dataUsingEncoding(NSUTF8StringEncoding)
let dataBytes = data?.bytes
let length = data?.length
let dataLength = UInt(length!)
let dataPointer = UnsafePointer<UInt8>(dataBytes!)
let operation: CCOperation = UInt32(kCCEncrypt)
let algoritm: CCAlgorithm = UInt32(kCCAlgorithmAES128)
let options: CCOptions = UInt32(kCCOptionECBMode + kCCOptionPKCS7Padding)
let cryptBufferSize = UInt(dataLength + kCCBlockSizeAES128)
var cryptBuffer = [UInt8](count: Int(cryptBufferSize), repeatedValue: 0)
var cryptBufferPointer = UnsafeMutablePointer<UInt8>(cryptBuffer)
var numBytesEncrypted = UnsafeMutablePointer<UInt>()
var cryptStatus = CCCrypt(operation, algoritm, options, keyPointer, keyLength, nil, dataPointer, dataLength, cryptBufferPointer, cryptBufferSize, numBytesEncrypted)
if UInt32(cryptStatus) == UInt32(kCCSuccess) {
let size = NSInteger(cryptBufferSize)
let encryptedData = NSData(bytes: cryptBufferPointer, length: size)
let encryptedString = NSString(data: encryptedData, encoding: NSUTF8StringEncoding)
println("Encrypted String = \(encryptedString)") // EXEC_BAD_ACCESS error
} else {
println("Error: \(cryptStatus)")
}
The encryptedData object shows the following info:
<279c2d0f d3ce2200 0dc10cc1 9df46e76 cb26f423 7c9bde76 f9d8d0e2 632acef9 74fb0614 4717422b 684d1889 e3ce882c 00000000 00000000 00000000 0000>
But the encryptedString shows 0x0000000000 in the debugger, and trying to println() it generates the EXEC_BAD_ACCESS error
Any idea what is missing?
Rgds....
Answer
Swift 2.0
Here is an example
If this is not exactly what is needed the methods should be a good example
Note: the key string is converted to data
Add Security.framework to the project
Add #import <CommonCrypto/CommonCryptor.h> to the bridging header.
let keyString = "12345678901234567890123456789012"
let keyData: NSData! = (keyString as NSString).dataUsingEncoding(NSUTF8StringEncoding) as NSData!
print("keyLength = \(keyData.length), keyData = \(keyData)")
let message = "Don´t try to read this text. Top Secret Stuff"
let data: NSData! = (message as NSString).dataUsingEncoding(NSUTF8StringEncoding) as NSData!
print("data length = \(data.length), data = \(data)")
let cryptData = NSMutableData(length: Int(data.length) + kCCBlockSizeAES128)!
let keyLength = size_t(kCCKeySizeAES256)
let operation: CCOperation = UInt32(kCCEncrypt)
let algoritm: CCAlgorithm = UInt32(kCCAlgorithmAES128)
let options: CCOptions = UInt32(kCCOptionECBMode + kCCOptionPKCS7Padding)
var numBytesEncrypted :size_t = 0
var cryptStatus = CCCrypt(operation,
algoritm,
options,
keyData.bytes, keyLength,
nil,
data.bytes, data.length,
cryptData.mutableBytes, cryptData.length,
&numBytesEncrypted)
if UInt32(cryptStatus) == UInt32(kCCSuccess) {
cryptData.length = Int(numBytesEncrypted)
print("cryptLength = \(numBytesEncrypted), cryptData = \(cryptData)")
// Not all data is a UTF-8 string so Base64 is used
let base64cryptString = cryptData.base64EncodedStringWithOptions(.Encoding64CharacterLineLength)
print("base64cryptString = \(base64cryptString)")
} else {
print("Error: \(cryptStatus)")
}
Output:
keyLength = 32, keyData = <31323334 35363738 39303132 33343536 37383930 31323334 35363738 39303132>
dataLength = 46, data = <446f6ec2 b4742074 72792074 6f207265 61642074 68697320 74657874 2e20546f 70205365 63726574 20537475 6666>
cryptLength = 48, cryptData = <118a32dc c23f7caa 883abc3c 1c7f0770 e200016b 2737acfa 17bb96fb a02b02a7 c147603b 06acd863 94bb8ff2 6cb14515>
base64cryptString = EYoy3MI/fKqIOrw8HH8HcOIAAWsnN6z6F7uW+6ArAqfBR2A7BqzYY5S7j/JssUUV
Swift 3
The iv is prefixed to the encrypted data
aesCBC128Encrypt will create a random IV and prefixed to the encrypted code.
aesCBC128Decrypt will use the prefixed IV during decryption.
Inputs are the data and key are Data objects. If an encoded form such as Base64 if required convert to and/or from in the calling method.
The key should be exactly 128-bits (16-bytes), 192-bits (24-bytes) or 256-bits (32-bytes) in length. If another key size is used an error will be thrown.
PKCS#7 padding is set by default.
This example requires Common Crypto
It is necessary to have a bridging header to the project:
#import <CommonCrypto/CommonCrypto.h>
Add the Security.framework to the project.
This is example, not production code.
enum AESError: Error {
case KeyError((String, Int))
case IVError((String, Int))
case CryptorError((String, Int))
}
// The iv is prefixed to the encrypted data
func aesCBCEncrypt(data:Data, keyData:Data) throws -> Data {
let keyLength = keyData.count
let validKeyLengths = [kCCKeySizeAES128, kCCKeySizeAES192, kCCKeySizeAES256]
if (validKeyLengths.contains(keyLength) == false) {
throw AESError.KeyError(("Invalid key length", keyLength))
}
let ivSize = kCCBlockSizeAES128;
let cryptLength = size_t(ivSize + data.count + kCCBlockSizeAES128)
var cryptData = Data(count:cryptLength)
let status = cryptData.withUnsafeMutableBytes {ivBytes in
SecRandomCopyBytes(kSecRandomDefault, kCCBlockSizeAES128, ivBytes)
}
if (status != 0) {
throw AESError.IVError(("IV generation failed", Int(status)))
}
var numBytesEncrypted :size_t = 0
let options = CCOptions(kCCOptionPKCS7Padding)
let cryptStatus = cryptData.withUnsafeMutableBytes {cryptBytes in
data.withUnsafeBytes {dataBytes in
keyData.withUnsafeBytes {keyBytes in
CCCrypt(CCOperation(kCCEncrypt),
CCAlgorithm(kCCAlgorithmAES),
options,
keyBytes, keyLength,
cryptBytes,
dataBytes, data.count,
cryptBytes+kCCBlockSizeAES128, cryptLength,
&numBytesEncrypted)
}
}
}
if UInt32(cryptStatus) == UInt32(kCCSuccess) {
cryptData.count = numBytesEncrypted + ivSize
}
else {
throw AESError.CryptorError(("Encryption failed", Int(cryptStatus)))
}
return cryptData;
}
// The iv is prefixed to the encrypted data
func aesCBCDecrypt(data:Data, keyData:Data) throws -> Data? {
let keyLength = keyData.count
let validKeyLengths = [kCCKeySizeAES128, kCCKeySizeAES192, kCCKeySizeAES256]
if (validKeyLengths.contains(keyLength) == false) {
throw AESError.KeyError(("Invalid key length", keyLength))
}
let ivSize = kCCBlockSizeAES128;
let clearLength = size_t(data.count - ivSize)
var clearData = Data(count:clearLength)
var numBytesDecrypted :size_t = 0
let options = CCOptions(kCCOptionPKCS7Padding)
let cryptStatus = clearData.withUnsafeMutableBytes {cryptBytes in
data.withUnsafeBytes {dataBytes in
keyData.withUnsafeBytes {keyBytes in
CCCrypt(CCOperation(kCCDecrypt),
CCAlgorithm(kCCAlgorithmAES128),
options,
keyBytes, keyLength,
dataBytes,
dataBytes+kCCBlockSizeAES128, clearLength,
cryptBytes, clearLength,
&numBytesDecrypted)
}
}
}
if UInt32(cryptStatus) == UInt32(kCCSuccess) {
clearData.count = numBytesDecrypted
}
else {
throw AESError.CryptorError(("Decryption failed", Int(cryptStatus)))
}
return clearData;
}
Example usage:
let clearData = "clearData0123456".data(using:String.Encoding.utf8)!
let keyData = "keyData890123456".data(using:String.Encoding.utf8)!
print("clearData: \(clearData as NSData)")
print("keyData: \(keyData as NSData)")
var cryptData :Data?
do {
cryptData = try aesCBCEncrypt(data:clearData, keyData:keyData)
print("cryptData: \(cryptData! as NSData)")
}
catch (let status) {
print("Error aesCBCEncrypt: \(status)")
}
let decryptData :Data?
do {
let decryptData = try aesCBCDecrypt(data:cryptData!, keyData:keyData)
print("decryptData: \(decryptData! as NSData)")
}
catch (let status) {
print("Error aesCBCDecrypt: \(status)")
}
Example Output:
clearData: <636c6561 72446174 61303132 33343536>
keyData: <6b657944 61746138 39303132 33343536>
cryptData: <92c57393 f454d959 5a4d158f 6e1cd3e7 77986ee9 b2970f49 2bafcf1a 8ee9d51a bde49c31 d7780256 71837a61 60fa4be0>
decryptData: <636c6561 72446174 61303132 33343536>
Notes:
One typical problem with CBC mode example code is that it leaves the creation and sharing of the random IV to the user. This example includes generation of the IV, prefixed the encrypted data and uses the prefixed IV during decryption. This frees the casual user from the details that are necessary for CBC mode.
For security the encrypted data also should have authentication, this example code does not provide that in order to be small and allow better interoperability for other platforms.
Also missing is key derivation of the key from a password, it is suggested that PBKDF2 be used is text passwords are used as keying material.
For robust production ready multi-platform encryption code see RNCryptor.