# Insecure encryption algorithm - Insecure Elliptic Curve

## Need

Secure encryption algorithm using strong elliptic curves

## Context

- Usage of Swift for iOS and macOS app development
- Usage of Foundation for building responsive and mobile-first web applications
- Usage of CommonCrypto for cryptographic operations

## Description

### Non compliant code

`import Foundation`

import CommonCrypto

let privateKey: SecKey = //...

let publicKey: SecKey = //...

let plainText = "Hello, World!"

let plainTextData = plainText.data(using: .utf8)!

let cipherTextData = SecKeyCreateEncryptedData(publicKey, .eciesEncryptionCofactorX963SHA256AESGCM, plainTextData as CFData, nil)! as Data

let decryptedData = SecKeyCreateDecryptedData(privateKey, .eciesEncryptionCofactorX963SHA256AESGCM, cipherTextData as CFData, nil)! as Data

let decryptedText = String(data: decryptedData, encoding: .utf8)

This Swift code snippet demonstrates encryption and decryption using the Elliptic Curve Integrated Encryption Scheme (ECIES). The encryption algorithm used is a combination of cofactor Diffie-Hellman key exchange (X963) and AES-GCM for symmetric encryption, with SHA-256 for hashing.

The plaintext "Hello, World!" is first converted to data. Then, the `SecKeyCreateEncryptedData`

function is used to encrypt the plaintext data using the public key. The result is the ciphertext data.

The `SecKeyCreateDecryptedData`

function is then used to decrypt the ciphertext data using the private key. The result is the decrypted data, which is converted back to a string.

The vulnerability lies in the use of a weak elliptic curve. The security of the encryption depends on the strength of the elliptic curve used. If a weak curve is used, the encrypted data can be decrypted by an attacker with sufficient computational resources.

### Steps

- Replace the insecure elliptic curve algorithm with a secure one.
- Use a strong elliptic curve algorithm such as ECDSA or ECDH.
- Ensure that the chosen elliptic curve algorithm is recommended by security experts.
- Update the code to use the secure elliptic curve algorithm for encryption and decryption.
- Verify that the chosen algorithm provides sufficient security for the application's needs.
- Consider consulting with a cryptography expert to ensure the correct implementation of the secure elliptic curve algorithm.

### Compliant code

`import Foundation`

import CommonCrypto

let privateKey: SecKey = //...

let publicKey: SecKey = //...

let plainText = "Hello, World!"

let plainTextData = plainText.data(using: .utf8)!

let cipherTextData = SecKeyCreateEncryptedData(publicKey, .eciesEncryptionStandardVariableIVX963SHA256AESGCM, plainTextData as CFData, nil)! as Data

let decryptedData = SecKeyCreateDecryptedData(privateKey, .eciesEncryptionStandardVariableIVX963SHA256AESGCM, cipherTextData as CFData, nil)! as Data

let decryptedText = String(data: decryptedData, encoding: .utf8)

The updated code now uses a secure elliptic curve algorithm for encryption and decryption. The insecure `.eciesEncryptionCofactorX963SHA256AESGCM`

algorithm has been replaced with the secure `.eciesEncryptionStandardVariableIVX963SHA256AESGCM`

algorithm.

This secure algorithm is recommended by security experts and provides sufficient security for the application's needs. It uses a variable initialization vector (IV) and combines the X9.63 key derivation function with the SHA-256 hash function and the AES-GCM encryption algorithm.

The `SecKeyCreateEncryptedData`

function is used to encrypt the plain text data using the public key and the secure elliptic curve algorithm. The `SecKeyCreateDecryptedData`

function is used to decrypt the cipher text data using the private key and the same secure elliptic curve algorithm.

The decrypted text is then converted back into a string using the UTF-8 encoding.

It is recommended to consult with a cryptography expert to ensure the correct implementation of the secure elliptic curve algorithm.