Swift CryptoKit AES Encryption and Javascript AES Decryption-CodePudding

I need to encrypt a value in an iOS app using CryptoKit and send it to a server, which will attempt to decrypt that value using a JavaScript Crypto Library (Right now, we're thinking CryptoJS, but open to other examples). There are a lot of questions on this topic, but I haven't come across any clear answers with updated examples, so I thought I'd describe my approach.

AES Encryption Using Swift

let key = "SomePrivateKey"
let dateToEncrypt = Date().toISOFormat().data(using: .utf8)
let val = try CryptoKit.AES.GCM.seal(
    datToEncrypt ?? Data(),
    using: .init(data: Array(key.utf8))
)
return val.ciphertext.base64EncodedString()

AES Decryption Using CryptoJS

var decrypted = CryptoJS.AES.decrypt(encrypted, myPassword);
return decrypted.toString(CryptoJS.enc.Utf8);

Expected Output

The decrypted string is an ISO Formatted Date

Actual Output

The decryption fails due to poorly formatted UTF-8 data, or the decryption succeeds but with a totally random value then what I expected (looks like a hex value of some sort)

CodePudding user response：

CryptoJS uses CBC mode by default, and doesn’t support GCM at all. You shouldn’t use CryptoJS at the best of times (the native and better-designed Web Crypto API is to be preferred), but especially not on the server, where Node.js has always had a native crypto module.

First, include the GCM nonce and tag, which are essential components:

return val.combined!.base64EncodedString()

Then, in Node.js, using the layout as described in the documentation for the combined property:

The data layout of the combined representation is: nonce, ciphertext, then tag.

// where `sealedBox` is a buffer obtained with `Buffer.from(encryptedString, 'base64')`
let nonce = sealedBox.slice(0, 12);
let ciphertext = sealedBox.slice(12, -16);
let tag = sealedBox.slice(-16);
let decipher = crypto.createDecipheriv('aes-128-gcm', key, nonce);
decipher.setAuthTag(tag);
let decrypted =
    Buffer.concat([decipher.update(ciphertext), decipher.final()])
    .toString('utf8');

Once that’s working, don’t forget to fix your key, because .init(data: Array(key.utf8)) is very uncomfortable (your AES keys should not be valid UTF-8).

If you’re starting with a password (for a good reason, not just because it seemed convenient), use a PBKDF to get key bytes. (Unfortunately, no PBKDF implementations are built into CryptoKit.)

… but if the good reason is that it’s a user-provided password and you’re claiming to provide security, please get someone experienced with use of cryptography to review your work.
Otherwise, generate a random key safely and decode it from a Base64 or hex string. No UTF-8.
```
node -p 'crypto.randomBytes(16).toString("base64")'
```
And get someone experienced with use of cryptography to review your work anyway.