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Insecure encryption algorithm - Anonymous cipher suites

Need​

Secure encryption algorithm and cipher suite selection

Context​

  • Usage of Swift for iOS and macOS app development
  • Usage of Foundation for building responsive and accessible web interfaces
  • Usage of Network for managing network connections and communication

Description​

Non compliant code​

import Foundation
import Network

let parameters = NWParameters.tls
parameters.allowLocalEndpointReuse = true
parameters.includePeerToPeer = true

let options = NWProtocolTLS.Options()
sec_protocol_options_set_cipher_suite(options.securityProtocolOptions, tls_ciphersuite_t(rawValue: UInt16(TLS_DH_anon_WITH_AES_128_CBC_SHA))!)

parameters.defaultProtocolStack.applicationProtocols.insert(options, at: 0)
let connection = NWConnection(to: NWEndpoint.hostPort(host: "localhost", port: 443), using: parameters)

In the above Swift code, we're creating a connection to a server using the Network Framework provided by Apple. This connection is configured to use the Transport Layer Security (TLS) protocol with certain parameters.

The critical vulnerability lies in this line of code:

sec_protocol_options_set_cipher_suite(options.securityProtocolOptions, tls_ciphersuite_t(rawValue: UInt16(TLS_DH_anon_WITH_AES_128_CBC_SHA))!)

Here, we're setting the cipher suite to be used for the TLS connection. The cipher suite defines the encryption algorithm and other security settings to be used for the connection. The problem is that we're using TLS_DH_anon_WITH_AES_128_CBC_SHA, an anonymous cipher suite.

Anonymous cipher suites are considered insecure because they don't provide any authentication. This means that while the data is encrypted, there's no way to verify the identity of the server we're connecting to. This opens up the possibility for man-in-the-middle attacks, where an attacker intercepts the connection and poses as the server.

In the context of a mobile application, this could lead to sensitive user data being exposed to attackers, or malicious data being sent to the user's device.

Steps​

  • Replace the insecure encryption algorithm with a secure one.
  • Use a strong cipher suite that provides confidentiality, integrity, and authentication.
  • Avoid using anonymous cipher suites.
  • Ensure that the TLS version used is secure and up-to-date.
  • Regularly update the encryption libraries and dependencies used in the application.
  • Perform a thorough security review and testing to identify any other potential vulnerabilities.

Compliant code​

import Foundation
import Network

let parameters = NWParameters.tls
parameters.allowLocalEndpointReuse = true
parameters.includePeerToPeer = true

let options = NWProtocolTLS.Options()
sec_protocol_options_set_cipher_suite(options.securityProtocolOptions, tls_ciphersuite_t(rawValue: UInt16(TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384))!)

parameters.defaultProtocolStack.applicationProtocols.insert(options, at: 0)
let connection = NWConnection(to: NWEndpoint.hostPort(host: "localhost", port: 443), using: parameters)

The original code was using an insecure encryption algorithm, specifically an anonymous cipher suite (TLS_DH_anon_WITH_AES_128_CBC_SHA). Anonymous cipher suites are considered insecure because they do not provide authentication, which can leave the application vulnerable to man-in-the-middle attacks.

The updated code replaces the insecure cipher suite with a secure one (TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384). This cipher suite provides confidentiality, integrity, and authentication, making it a much more secure choice.

In addition to changing the cipher suite, it's also important to ensure that the TLS version used by the application is secure and up-to-date. The NWParameters.tls used in the code should be configured to use a secure version of TLS.

Finally, it's recommended to regularly update the encryption libraries and dependencies used in the application, and to perform a thorough security review and testing to identify any other potential vulnerabilities.

References​

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