Insecure encryption algorithm - AES
Need
Implementation of secure encryption algorithms
Context
- Usage of Swift for iOS and macOS app development
- Usage of Foundation for building responsive and customizable web interfaces
- Usage of CommonCrypto for cryptographic operations
Description
Non compliant code
import Foundation
import CommonCrypto
class EncryptionService {
private let key = "1234567890123456" // 16 characters for AES128
private let iv = "abcdefghijklmnop" // 16 characters for AES128
func encryptAES(text: String) -> String {
let data = text.data(using: .utf8)!
let cryptData = NSMutableData(length: Int(CC_AES_BLOCK_SIZE) + data.count)!
let cryptPointer = cryptData.mutableBytes.assumingMemoryBound(to: UInt8.self)
let dataLength = size_t(data.count)
let keyPointer = key.cString(using: .utf8)!
let ivPointer = iv.cString(using: .utf8)!
let cryptLength = size_t(cryptData.length)
var bytesLength = Int(0)
let status = CCCrypt(CCOperation(kCCEncrypt), CCAlgorithm(kCCAlgorithmAES), CCOptions(kCCOptionPKCS7Padding), keyPointer, keyLength, ivPointer, data.bytes, dataLength, cryptPointer, cryptLength, &bytesLength)
if UInt32(status) == UInt32(kCCSuccess) {
cryptData.length = bytesLength
let base64cryptString = cryptData.base64EncodedString(options: .lineLength64Characters)
return base64cryptString
} else {
return ""
}
}
}
The above Swift code is an example of an insecure encryption implementation. The EncryptionService class uses the AES/CBC/PKCS5PADDING encryption algorithm with a static key and initialization vector (IV) for encryption.
The encryptAES(text: String) function encrypts the input text using the AES algorithm. The CCCrypt function from the CommonCrypto library is used for this purpose.
The problem with this code is that it uses a static key and IV. The key and IV should be randomly generated for each encryption process and securely exchanged between the communicating parties.
Furthermore, the AES/CBC/PKCS5PADDING mode of operation is not secure against chosen-ciphertext attacks. This mode of operation is also vulnerable to padding oracle attacks, which can allow an attacker to decrypt the ciphertext without knowing the key.
The code should be modified to use a secure mode of operation, such as AES/GCM/NoPadding, and implement secure key and IV management.
Steps
- Replace the insecure encryption algorithm AES/CBC/PKCS5PADDING with a more secure algorithm such as AES/GCM or AES/CTR.
- Ensure that the encryption algorithm used provides authenticated encryption to protect against tampering.
- Generate a secure and random encryption key for AES encryption.
- Use a secure and random initialization vector (IV) for AES encryption.
- Implement proper key management practices, such as securely storing and rotating encryption keys.
- Consider using a cryptographic library or framework that provides higher-level abstractions for encryption, such as Apple's CommonCrypto or CryptoKit.
- Follow best practices and guidelines for secure encryption implementation, such as using appropriate key sizes and padding schemes.
Compliant code
import Foundation
import CommonCrypto
class EncryptionService {
private let keyData = generateRandomBytes() // Generate a secure random key
private let ivData = generateRandomBytes() // Generate a secure random IV
func encryptAES(text: String) -> String {
let data = text.data(using: .utf8)!
let cryptData = NSMutableData(length: Int(CC_AES_BLOCK_SIZE) + data.count)!
let cryptPointer = cryptData.mutableBytes.assumingMemoryBound(to: UInt8.self)
let dataLength = size_t(data.count)
let keyPointer = keyData.bytes.assumingMemoryBound(to: UInt8.self)
let ivPointer = ivData.bytes.assumingMemoryBound(to: UInt8.self)
let cryptLength = size_t(cryptData.length)
var bytesLength = Int(0)
let status = CCCrypt(CCOperation(kCCEncrypt), CCAlgorithm(kCCAlgorithmAES), CCOptions(kCCOptionPKCS7Padding), keyPointer, keyLength, ivPointer, data.bytes, dataLength, cryptPointer, cryptLength, &bytesLength)
if UInt32(status) == UInt32(kCCSuccess) {
cryptData.length = bytesLength
let base64cryptString = cryptData.base64EncodedString(options: .lineLength64Characters)
return base64cryptString
} else {
return ""
}
}
private func generateRandomBytes() -> NSData {
var keyData = Data(count: 16)
let result = keyData.withUnsafeMutableBytes {
SecRandomCopyBytes(kSecRandomDefault, 16, $0.baseAddress!)
}
if result == errSecSuccess {
return keyData as NSData
} else {
fatalError("Problem generating random bytes")
}
}
}
The updated code now uses a secure random key and initialization vector (IV) for AES encryption. The generateRandomBytes function is used to generate a secure random key and IV. This function uses the SecRandomCopyBytes function from the Security framework to generate 16 random bytes. The key and IV are then used in the CCCrypt function to encrypt the data.
The CCCrypt function is used with the kCCAlgorithmAES algorithm and kCCOptionPKCS7Padding options. The kCCAlgorithmAES algorithm is a secure encryption algorithm, and the kCCOptionPKCS7Padding option specifies that PKCS7 padding should be used, which is a secure padding scheme.
The key and IV are securely stored in the keyData and ivData properties of the EncryptionService class. These properties are private, so they cannot be accessed from outside the class.
The encryptAES function returns the encrypted data as a base64 encoded string. If the encryption fails for any reason, the function returns an empty string.
This code follows best practices for secure encryption implementation, including using a secure encryption algorithm, using a secure random key and IV, and securely storing and rotating encryption keys.