AES encryption in swift

by

Be sure to use the same parameters which seem to be AES with CBC mode with iv, PKCS5Padding (actually PKCS#7) padding and a 16-byte (128-bit) key.

PKCS#5 padding and PKCS#7 padding are essentially the same, sometimes for historic reasons PKCS#5 padding is specified for use with AES but the actual padding is PKCS#7.

Make sure the encodings of the key, iv and encrypted data all match. Hex dump them on both platforms to ensure they are identical. Encryption functions are not difficult to use, if all the input parameters are correct the output will be correct.

To make this more secure the iv should be random bytes and prepended to the encrypted data for use during decryption.

The Cross platform AES encryption uses a 256-bit key so will not work as-is.

Example:

Swift 2

// operation: kCCEncrypt or kCCDecrypt
func testCrypt(data data:[UInt8], keyData:[UInt8], ivData:[UInt8], operation:Int) -> [UInt8]? {
    let cryptLength  = size_t(data.count+kCCBlockSizeAES128)
    var cryptData    = [UInt8](count:cryptLength, repeatedValue:0)

    let keyLength             = size_t(kCCKeySizeAES128)
    let algoritm: CCAlgorithm = UInt32(kCCAlgorithmAES128)
    let options:  CCOptions   = UInt32(kCCOptionPKCS7Padding)

    var numBytesEncrypted :size_t = 0

    let cryptStatus = CCCrypt(CCOperation(operation),
                              algoritm,
                              options,
                              keyData, keyLength,
                              ivData,
                              data, data.count,
                              &cryptData, cryptLength,
                              &numBytesEncrypted)

    if UInt32(cryptStatus) == UInt32(kCCSuccess) {
        cryptData.removeRange(numBytesEncrypted..<cryptData.count)

    } else {
        print("Error: \(cryptStatus)")
    }

    return cryptData;
}

let message       = "Don´t try to read this text. Top Secret Stuff"
let messageData   = Array(message.utf8)
let keyData       = Array("12345678901234567890123456789012".utf8)
let ivData        = Array("abcdefghijklmnop".utf8)
let encryptedData = testCrypt(data:messageData,   keyData:keyData, ivData:ivData, operation:kCCEncrypt)!
let decryptedData = testCrypt(data:encryptedData, keyData:keyData, ivData:ivData, operation:kCCDecrypt)!
var decrypted     = String(bytes:decryptedData, encoding:NSUTF8StringEncoding)!

print("message:       \(message)");
print("messageData:   \(NSData(bytes:messageData,   length:messageData.count))");
print("keyData:       \(NSData(bytes:keyData,       length:keyData.count))");
print("ivData:        \(NSData(bytes:ivData,        length:ivData.count))");
print("encryptedData: \(NSData(bytes:encryptedData, length:encryptedData.count))");
print("decryptedData: \(NSData(bytes:decryptedData, length:decryptedData.count))");
print("decrypted:     \(String(bytes:decryptedData,encoding:NSUTF8StringEncoding)!)");

Output:

message:       Don´t try to read this text. Top Secret Stuff  
messageData:   446f6ec2 b4742074 72792074 6f207265 61642074 68697320 74657874 2e20546f 70205365 63726574 20537475 6666  
keyData:       31323334 35363738 39303132 33343536 37383930 31323334 35363738 39303132  
ivData:        61626364 65666768 696a6b6c 6d6e6f70  
encryptedData: b1b6dc17 62eaf3f8 baa1cb87 21ddc35c dee803ed fb320020 85794848 21206943 a85feb5b c8ee58fc d6fb664b 96b81114  
decryptedData: 446f6ec2 b4742074 72792074 6f207265 61642074 68697320 74657874 2e20546f 70205365 63726574 20537475 6666  
decrypted:     Don´t try to read this text. Top Secret Stuff

Swift 3 with [UInt8] type

func testCrypt(data:[UInt8], keyData:[UInt8], ivData:[UInt8], operation:Int) -> [UInt8]? {
    let cryptLength  = size_t(data.count+kCCBlockSizeAES128)
    var cryptData    = [UInt8](repeating:0, count:cryptLength)

    let keyLength             = size_t(kCCKeySizeAES128)
    let algoritm: CCAlgorithm = UInt32(kCCAlgorithmAES128)
    let options:  CCOptions   = UInt32(kCCOptionPKCS7Padding)

    var numBytesEncrypted :size_t = 0

    let cryptStatus = CCCrypt(CCOperation(operation),
                              algoritm,
                              options,
                              keyData, keyLength,
                              ivData,
                              data, data.count,
                              &cryptData, cryptLength,
                              &numBytesEncrypted)

    if UInt32(cryptStatus) == UInt32(kCCSuccess) {
        cryptData.removeSubrange(numBytesEncrypted..<cryptData.count)

    } else {
        print("Error: \(cryptStatus)")
    }

    return cryptData;
}

Swift 3 & 4 with Data type

func testCrypt(data:Data, keyData:Data, ivData:Data, operation:Int) -> Data {
    let cryptLength  = size_t(data.count + kCCBlockSizeAES128)
    var cryptData = Data(count:cryptLength)

    let keyLength             = size_t(kCCKeySizeAES128)
    let options   = CCOptions(kCCOptionPKCS7Padding)


    var numBytesEncrypted :size_t = 0

    let cryptStatus = cryptData.withUnsafeMutableBytes {cryptBytes in
        data.withUnsafeBytes {dataBytes in
            ivData.withUnsafeBytes {ivBytes in
                keyData.withUnsafeBytes {keyBytes in
                    CCCrypt(CCOperation(operation),
                              CCAlgorithm(kCCAlgorithmAES),
                              options,
                              keyBytes, keyLength,
                              ivBytes,
                              dataBytes, data.count,
                              cryptBytes, cryptLength,
                              &numBytesEncrypted)
                }
            }
        }
    }

    if UInt32(cryptStatus) == UInt32(kCCSuccess) {
        cryptData.removeSubrange(numBytesEncrypted..<cryptData.count)

    } else {
        print("Error: \(cryptStatus)")
    }

    return cryptData;
}

let message     = "Don´t try to read this text. Top Secret Stuff"
let messageData = message.data(using:String.Encoding.utf8)!
let keyData     = "12345678901234567890123456789012".data(using:String.Encoding.utf8)!
let ivData      = "abcdefghijklmnop".data(using:String.Encoding.utf8)!

let encryptedData = testCrypt(data:messageData,   keyData:keyData, ivData:ivData, operation:kCCEncrypt)
let decryptedData = testCrypt(data:encryptedData, keyData:keyData, ivData:ivData, operation:kCCDecrypt)
var decrypted     = String(bytes:decryptedData, encoding:String.Encoding.utf8)!

Example from sunsetted documentation section:

AES encryption in CBC mode with a random IV (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.

More Related Contents:

  1. Issue using CCCrypt (CommonCrypt) in Swift
  2. Importing CommonCrypto in a Swift framework
  3. AES Encrypt and Decrypt
  4. AES/CBC/PKCS5Padding in iOS objective c result differs from Android
  5. String extensions toDate() is crash some device
  6. Removing ”\” from output
  7. How to get the indexpath.row when an element is activated?
  8. How to return value from Alamofire
  9. How do I add text to an image in iOS Swift?
  10. Swift GET request with parameters
  11. How to iterate for loop in reverse order in swift?
  12. Check if property is set in Core Data?
  13. How to crop UIImage on oval shape or circle shape?
  14. Using isKindOfClass with Swift
  15. How to create a Scroll View with a page control using swift? [closed]
  16. Swift replace substring regex
  17. Alamofire invalid value around character 0
  18. Immutable/Mutable Collections in Swift
  19. Decode base64URL to base64 — Swift
  20. Xcode 10.2 with Swift 5.0 compiler – protocol inheritance issue
  21. Upload image with multipart form-data iOS in Swift
  22. Add swipe to delete UITableViewCell
  23. Open PDF file using swift
  24. Dynamically increase height of UILabel & TableView Cell?
  25. Default tab bar item colors using swift Xcode 6
  26. How shouldChangeCharactersInRange works in Swift?
  27. How to get the front camera in Swift?
  28. GM release of Xcode 6 compile
  29. How do I convert a date/time string into a different date string?
  30. Difference between static function and singleton class in swift [closed]

Leave a Comment