ECIES Decrypting a message fetched from API giving me bad public key

[Mickellz]

Hello. So I have been trying to post the encrypted message as a string hex value to an api and when I retrieve it, buffer the object, and decrypt, it gives me "bad public key". I am not sure why this happens, but how can I effectively store a message as json on an api and fetch it back for client siding decryption?

[JBaczuk]

@Mickellz Sorry, there are examples on the homepage, whether or not you are using an API should make no difference. Can you provide any code, to help you debug?

[kktcell]

Same problem

[giviz]

This is due to the check on here : https://github.com/bitchan/eccrypto/blob/master/browser.js#L190

When you get the stored message from the API and decode it using something like that

    let parts = blob.split('|');
    let cypher = {
      ciphertext: Uint8Array.from(this.fromBase64(parts[0])),
      ephemPublicKey: Uint8Array.from(this.fromBase64(parts[1])),
      iv: Uint8Array.from(this.fromBase64(parts[2])),
      mac: Uint8Array.from(this.fromBase64(parts[3])), 
    }

It fails because the Buffer.isBuffer check on the Uint8Array of the publicKey fails.
From what I can see, the issue could be that this Uint8Array has a prototype of TypedArray and not Uint8Array like the one generated by eccrypto directly (just guessing here)

By commenting that assert, the code works properly and the message is decoded properly too.

Here is the full code used to encode and decode I'm using :

  public async encrypt(publicKey: string, message: string) : Promise<string> {
    let cypher = await this.eccrypto.encrypt(publicKey, this.stringToArrayBuffer(message));
    let blob = [
      this.toBase64(cypher.ciphertext),
      this.toBase64(cypher.ephemPublicKey),
      this.toBase64(cypher.iv),
      this.toBase64(cypher.mac),
    ].join('|');
    return blob;
  }

  public async decrypt(privateKey: Uint8Array, blob: string) : Promise<string> {
    let parts = blob.split('|');
    let cypher = {
      ciphertext: Uint8Array.from(this.fromBase64(parts[0])),
      ephemPublicKey: Uint8Array.from(this.fromBase64(parts[1])),
      iv: Uint8Array.from(this.fromBase64(parts[2])),
      mac: Uint8Array.from(this.fromBase64(parts[3])), 
    }

    let message = await this.eccrypto.decrypt(privateKey, cypher);
    return this.arrayBufferToString(message);
  }

Edit :

To work with bitcoin keys and not keys generated by eccrypto with the helpers, I also had to comment :

• line 189
  
• Force true on https://github.com/bitchan/eccrypto/blob/master/browser.js#L24

Otherwise, while using eccrypto in the browser it's not working because of the same issue.
With all of that commented, the message encode and decode properly.

Let me know if I can provide more details :)

Edit 2 :

There is a similar issue with the sign and verify methods, I had to replace :

assert(msg.length <= 32, "Message is too long");

By

let length = msg.length;
assert(length <= 32, "Message is too long");

Otherwise it's failing, even if the array is in fact at the correct 32 size :/

[aaronik]

@giviz, I'm struggling with storing the private key somewhere, and using that later to (re)generate the public key. I'm having troubles with strings and buffers..

Can you share with us your implementations of this.stringToArrayBuffer and this.fromBase64?

Or if @JBaczuk you're around, or anybody else knows, how exactly does one go from the Uint8Array that eccrypto.generatePrivate() returns to a string and then back again? Preferably a base64 string?

[aaronik]

You know what, I finally figured it out (not a minute too soon). This post was instrumental.

To go from buffer to string: const s = eccrypto.generatePrivate().toString(<encoding>)
And from string to buffer: const b = Buffer.from(s, <encoding>)

where encoding works for me best as either 'base64' or 'hex', and I'm going with hex now.

[giviz]

@aaronik

I'm glad you figured it out, I was actually writing you an email to share my own implementation !
Beware that your current solution will work well in nodejs but not in the browser as it doesn't support Buffer.

For that, you have to take a whole other path... but if it's not required on your use case you're good to go !

[aaronik]

Actually i have accepted the fact that i need to use browserify 🙂 But if you have a way around that i am all ears!

…

On Wed, Mar 16, 2022, 4:37 PM giviz ***@***.***> wrote: @aaronik <https://github.com/Aaronik> I'm glad you figured it out, I was actually writing you an email to share my own implementation ! Beware that your current solution will work well in nodejs but not in the browser as it doesn't support Buffer. For that, you have to take a whole other path... but if it's not required on your use case you're good to go ! — Reply to this email directly, view it on GitHub <#75 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAKDMOIKWEUAOK7LGLGYDXLVAJWD3ANCNFSM4XP4KQUQ> . Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>. You are receiving this because you were mentioned.Message ID: ***@***.***>