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Attack Tree Analysis for krzyzanowskim/cryptoswift

Objective: Decrypt sensitive data encrypted by the application using CryptoSwift, or forge authenticated messages/data.

Attack Tree Visualization

                                      Decrypt Data / Forge Messages
                                                  |
                                  -----------------------------------
                                  |
                      **Exploit CryptoSwift Implementation**
                                  |
                  -----------------------------------
                  |
             **3. Incorrect API Usage [HIGH RISK]**
                  |
                  ----------
                  |        |
               **3.1**  **3.2**
               **IV**   **Key**
               **Reuse** **Reuse**
               **[CRITICAL]** **[CRITICAL]**

Attack Tree Path: 3. Incorrect API Usage [HIGH RISK]

  • Description: This category encompasses vulnerabilities arising from the application developer's misuse of the CryptoSwift library. Even if the library itself is perfectly secure, incorrect usage can completely undermine its security guarantees. This is the most likely source of exploitable vulnerabilities.
  • Likelihood: High to Very High. This is a very common problem in real-world applications.
  • Impact: Very High. Can lead to complete decryption of data or forging of authenticated messages.
  • Effort: Low to Medium. Exploiting these vulnerabilities is often relatively straightforward once they are identified.
  • Skill Level: Intermediate. Requires understanding of cryptographic principles but not necessarily expert-level knowledge.
  • Detection Difficulty: Medium. Code reviews, static analysis tools, and security audits can often detect these issues.

Attack Tree Path: 3.1 IV Reuse [CRITICAL]

  • Description: Reusing the same Initialization Vector (IV) with the same key in modes like CBC (Cipher Block Chaining) or GCM (Galois/Counter Mode) is a catastrophic error. The IV is supposed to be a unique, unpredictable value for each encryption operation. Reusing it makes the encryption deterministic and allows an attacker to:
    • CBC Mode: If the same plaintext block is encrypted multiple times with the same key and IV, the resulting ciphertext blocks will be identical. This leaks information about the plaintext. With enough ciphertext, an attacker can often decrypt the entire message.
    • GCM Mode: IV reuse completely breaks the authentication properties of GCM. An attacker can forge authenticated messages and potentially decrypt data.
  • Example: 
    // INCORRECT: Reusing the same IV
let key = "This is a secret key".bytes
let iv = "This is a bad IV".bytes // This IV should be generated randomly for EACH encryption!

let message1 = "Message 1".bytes
let ciphertext1 = try! AES(key: key, blockMode: CBC(iv: iv), padding: .pkcs7).encrypt(message1)

let message2 = "Message 2".bytes
let ciphertext2 = try! AES(key: key, blockMode: CBC(iv: iv), padding: .pkcs7).encrypt(message2) // IV REUSED!

// ciphertext1 and ciphertext2 will reveal patterns if message1 and message2 share common prefixes.
  • Likelihood: Medium to High. A common mistake due to misunderstanding of IV requirements.
  • Impact: Very High. Complete loss of confidentiality and/or integrity.
  • Effort: Very Low. Exploiting IV reuse is often trivial once identified.
  • Skill Level: Intermediate.
  • Detection Difficulty: Medium. Code reviews and static analysis tools can often detect this.

Attack Tree Path: 3.2 Key Reuse [CRITICAL]

  • Description: Using the same cryptographic key for multiple purposes (e.g., encryption and authentication, or encrypting different types of data with the same key) is a dangerous practice. It can create unexpected vulnerabilities and allow attacks that would not be possible if keys were used for a single, specific purpose.
  • Example: 
    // INCORRECT: Reusing the same key for encryption and authentication
let key = "This is a secret key".bytes

// Encryption
let message = "Secret message".bytes
let ciphertext = try! AES(key: key, blockMode: .cbc, padding: .pkcs7).encrypt(message)

// Authentication (using the same key!)
let hmac = try! HMAC(key: key, variant: .sha256).authenticate(message)

// This is vulnerable!  An attacker might be able to use information from the HMAC
// to help decrypt the ciphertext, or vice-versa.
  • Likelihood: Medium. Another common mistake, especially in applications without a well-defined key management strategy.
  • Impact: High to Very High. The specific consequences depend on how the key is reused, but it often leads to significant security breaches.
  • Effort: Low to Medium. The effort required to exploit key reuse depends on the specific vulnerability it creates.
  • Skill Level: Intermediate.
  • Detection Difficulty: Medium. Code reviews and security audits can often identify key reuse.