Unable to verify Go generated ECDSA signature using JS

php editor Xiaoxin encountered a problem when using Go language to generate ECDSA signatures, that is, JS could not be used for verification. The solution to this problem is to add some additional fields to the Go code to ensure the correctness of the signature. By making some modifications to the Go code, we can solve this problem and enable JS to correctly verify the ECDSA signature generated by Go. This article will introduce you to the specific solutions and steps in detail.

Question content

I ran into a small problem, (my assumption is that there is a small thing holding me back, but I don't know what), as stated in the title.

I'll start by outlining what I'm doing and then provide everything I have.

Project Overview

I'm hashing the file using SHA-256 in the mobile app and signing the hash on the backend using the ECDSA P-256 key. And then this goes on and on. If the user wants, he can verify the integrity of the file by hashing the file again and looking up the hash and getting the hash, some metadata, and the signature.

In order to verify that the data was submitted to my application and not a third party (the hashes remain in the blockchain, but that is not important for this problem), the application will try to verify the signature using the public key. This work is good.

Now I want to add this option to my website as well, but the problem is. If I use the jsrsasign or webcrypto api, my signature is invalid.

data

• Signature example: 3045022100f28c29042a6d766810e21f2c0a1839f93140989299cae1d37b49a454373659c802203d0967be0696686414fe2efed3a71bc1639d066 ee1 27cfb7c0ad369521459d00
• Public key:

-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEq6iOuQeIhlhywCjo5yoABGODOJRZ
c6/L8XzUYEsocCbc/JHiByGjuB3G9cSU2vUi1HUy5LsCtX2wlHSEObGVBw==
-----END PUBLIC KEY-----

• Hash value: bb5dbfcb5206282627254ab23397cda842b082696466f2563503f79a5dccf942

script

JS code

<code>const validHash = document.getElementById("valid-hash");
const locationEmbedded = document.getElementById("location-embedded")
const signatureValid = document.getElementById("valid-sig")
const fileSelector = document.getElementById('file-upload');
const mcaptchaToken = document.getElementById("mcaptcha__token")
const submission = document.getElementById("submission")
let publicKey;

fileSelector.addEventListener("change", (event) => {
    document.getElementsByClassName("file-upload-label")[0].innerHTML = event.target.files[0].name
})
submission.addEventListener('click', async (event) => {
    let token = mcaptchaToken.value
    if (token == null || token == "") {
        alert("Please activate the Captcha!")
        return
    }
    const fileList = fileSelector.files;
    if (fileList[0]) {
        const file = fileList[0]
        const fileSize = file.size;
        let fileData = await readBinaryFile(file)
        let byteArray = new Uint8Array(fileData);
        const bytes = await hashFile(byteArray)
        try {
            let resp = await callApi(toHex(bytes), token)
            validHash.innerHTML = "\u2713"

            const mediainfo = await MediaInfo({ format: 'object' }, async (mediaInfo) => { // Taken from docs
                mediaInfo.analyzeData(() => file.size, (chunkSize, offset) => {
                    return new Promise((resolve, reject) => {
                        const reader = new FileReader()
                        reader.onload = (event) => {
                            if (event.target.error) {
                                reject(event.target.error)
                            }
                            resolve(new Uint8Array(event.target.result))
                        }
                        reader.readAsArrayBuffer(file.slice(offset, offset + chunkSize))
                    })
                })
                try {
                    let tags = mediaInfo.media.track[0].extra
                    latitude = tags.LATITUDE
                    longitude = tags.LONGITUDE
                    if (latitude && longitude) {
                        locationEmbedded.innerHTML = "\u2713"
                    } else {
                        locationEmbedded.innerHTML = "\u2717"
                    }
                } catch (e) {
                    locationEmbedded.innerHTML = "\u2717"
                }
               
            })
            if (publicKey == undefined) {
                let req = await fetch("/publickey")
                if (req.ok) {
                    publicKey = await req.text()
                } else {
                    throw "Could not get public key"
                }
            }

            let signature = resp.data.comment
            if (signature == null || signature == "") {
                throw "No signature found"
            }
            //const timeStamps = resp.data.timestamps
            const hashString = resp.data.hash_string
            console.log(hashString)
            if (hashString !== toHex(bytes)) {
                validHash.innerHTML = "\u2717"
            } else {
                validHash.innerHTML = "\u2713"
            }
            const result = await validateSignature(publicKey, signature, hashString)
            console.log("Valid signature: " + result)
            if (result) {
                signatureValid.innerHTML = "\u2713"
            } else {
                signatureValid.innerHTML = "\u2717"
            }
            mcaptchaToken.value = ""
        } catch (e) {
            alert("Error: " + e)
            window.location.reload()
        }

    } else {
        alert("No file selected");
    }
});


function toHex(buffer) {
    return Array.prototype.map.call(buffer, x => ('00' + x.toString(16)).slice(-2)).join('');
}

async function callApi(hash, token) {
    const url = "/verify";
    let resp = await fetch(url, {
        headers: { "X-MCAPTCHA-TOKEN": token },
        method: "POST",
        body: JSON.stringify({ hash: hash })
    })
    if (resp.ok) {
        return await resp.json();
    } else {
        if (resp.status == 401) {
            throw resp.status
        } else {
            console.log(resp)
            throw "Your hash is either invalid or has not been submitted via the Decentproof App!"
        }
    }
}

async function hashFile(byteArray) {
    let hashBytes = await window.crypto.subtle.digest('SHA-256', byteArray);
    return new Uint8Array(hashBytes)
}

async function validateSignature(key, signature,hashData) {
    const importedKey = importPublicKey(key)
    const sig = new KJUR.crypto.Signature({"alg": "SHA256withECDSA"});
    sig.init(importedKey)
    sig.updateHex(hashData);
    return sig.verify(signature)
}

function readBinaryFile(file) {
    return new Promise((resolve, reject) => {
        var fr = new FileReader();
        fr.onload = () => {
            resolve(fr.result)
        };
        fr.readAsArrayBuffer(file);
    });
}

function importPublicKey(pem) {
    console.log(pem)
    return KEYUTIL.getKey(pem); 
  }

  function hexToBytes(hex) {
    for (var bytes = [], c = 0; c < hex.length; c += 2)
    bytes.push(parseInt(hex.substr(c, 2), 16));
    return new Uint8Array(bytes);
}
</code>

Application verification code (Flutter Dart)

<code>import 'dart:convert';
import 'package:convert/convert.dart';
import 'dart:typed_data';
import 'package:basic_utils/basic_utils.dart';
import 'package:decentproof/features/verification/interfaces/ISignatureVerifcationService.dart';
import 'package:pointycastle/asn1/asn1_parser.dart';
import 'package:pointycastle/asn1/primitives/asn1_integer.dart';
import 'package:pointycastle/signers/ecdsa_signer.dart';

class SignatureVerificationService implements ISignatureVerificationService {
  late final ECPublicKey pubKey;
  SignatureVerificationService() {
    pubKey = loadAndPrepPubKey();
  }

  final String pemPubKey = """
-----BEGIN EC PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEq6iOuQeIhlhywCjo5yoABGODOJRZ
c6/L8XzUYEsocCbc/JHiByGjuB3G9cSU2vUi1HUy5LsCtX2wlHSEObGVBw==
-----END EC PUBLIC KEY-----
""";

  ECSignature loadAndConvertSignature(String sig) {
    //Based on: https://github.com/bcgit/pc-dart/issues/159#issuecomment-1105689978
    Uint8List bytes = Uint8List.fromList(hex.decode(sig));
    ASN1Parser p = ASN1Parser(bytes);
    //Needs to be dynamic or otherwise throws odd errors
    final seq = p.nextObject() as dynamic;
    ASN1Integer ar = seq.elements?[0] as ASN1Integer;
    ASN1Integer as = seq.elements?[1] as ASN1Integer;
    BigInt r = ar.integer!;
    BigInt s = as.integer!;
    return ECSignature(r, s);
  }

  ECPublicKey loadAndPrepPubKey() {
    return CryptoUtils.ecPublicKeyFromPem(pemPubKey);
  }

  @override
  bool verify(String hash, String sig) {
    ECSignature convertedSig = loadAndConvertSignature(sig);
    final ECDSASigner signer = ECDSASigner();
    signer.init(false, PublicKeyParameter<ECPublicKey>(loadAndPrepPubKey()));
    Uint8List messageAsBytes = Uint8List.fromList(utf8.encode(hash));
    return signer.verifySignature(messageAsBytes, convertedSig);
  }
}
</code>

Key generation script (Go)

<code>package main

import (
    "crypto/ecdsa"
    "crypto/elliptic"
    "crypto/rand"
    "crypto/x509"
    "encoding/pem"
    "flag"
    "fmt"
    "os"
)

func main() {
    var outPutDir string
    var outPutFileName string
    flag.StringVar(&outPutDir, "out", "./", "Output directory")
    flag.StringVar(&outPutFileName, "name", "key", "Output file name e.g key, my_project_key etc. Adding .pem is not needed")
    flag.Parse()
    key, err := generateKeys()
    if err != nil {
        fmt.Printf("Something went wrong %d", err)
        return
    }
    err = saveKeys(key, outPutDir, outPutFileName)
    if err != nil {
        fmt.Printf("Something went wrong %d", err)
        return
    }
    fmt.Printf("Keys generated and saved to %s%s.pem and %spub_%s.pem", outPutDir, outPutFileName, outPutDir, outPutFileName)

}

func generateKeys() (*ecdsa.PrivateKey, error) {
    return ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
}
func saveKeys(key *ecdsa.PrivateKey, outPutDir string, outPutFileName string) error {
    bytes, err := x509.MarshalECPrivateKey(key)
    if err != nil {
        return err
    }
    privBloc := pem.Block{Type: "EC PRIVATE KEY", Bytes: bytes}
    privKeyFile, err := os.Create(outPutDir + outPutFileName + ".pem")
    if err != nil {
        return err
    }
    defer privKeyFile.Close()
    err = pem.Encode(privKeyFile, &privBloc)
    if err != nil {
        return err
    }

    bytes, err = x509.MarshalPKIXPublicKey(&key.PublicKey)
    pubBloc := pem.Block{Type: "EC Public KEY", Bytes: bytes}
    pubKeyFile, err := os.Create(outPutDir + "pub_" + outPutFileName + ".pem")
    if err != nil {
        return err
    }
    defer pubKeyFile.Close()
    err = pem.Encode(pubKeyFile, &pubBloc)
    if err != nil {
        return err
    }

    return nil
}
</code>

Link to signature wrapper script: link

My attempt

• I've tested using two new key pairs (and your library) to sign some sample data to see if what's in the key is wrong, and it's not the case
• I have tested the signed data using your library and my private key and verified it with my public key to see if my private key is corrupt and it is not the case
• I have tried all operations of the Network Encryption API without success
• I tried loading the ECDSA public key and using new KJUR.crypto.ECDSA({"curve":"secp256r1"}).verifyHex(hash,signature,pubKeyHex) with With the above data, it doesn't work (only tested in browser console)
• I used Firefox and Safari to see if there were any differences, but nothing changed
• I tried passing the hash value as a string via sig.updateString(hashData) without success
• There are some other smaller changes
• Comparing the hashes, r&s signatures on the website and the app website, everything is as expected.
• I have tracked the entire process from front-end to back-end and no data has changed

My last attempt was the fourth because at least from my understanding if you use the regular way (which I did in the script above) your data will be hashed, as far as I'm concerned In terms of this, it's the opposite of productive, because I've already got the hash value, so if it's hashed twice, of course, it won't match. But for reasons I don't understand, I still get false as the return value.

One last thought, if using P-256 signature, could the problem be that the go ecdsa library truncates the message to 32 bytes? Maybe not so in JS?

Workaround

Validation in JavaScript code is incompatible with Dart code for two reasons:

• 首先，JavaScript代码使用KJUR.crypto.Signature ()，它隐式对数据进行哈希处理。由于数据已经被散列，这会导致双重散列。在 Dart 方面，不会发生隐式哈希（因为 ECDSASigner())。
  为了避免 JavaScript 端的隐式哈希并与 Dart 代码兼容，KJUR.crypto.ECDSA() 可以用来代替 KJUR.crypto.Signature()。
• 其次，JavaScript 代码中的 updateHex() 对十六进制编码的哈希值执行十六进制解码，而在 Dart 代码中，十六进制编码的哈希值是 UTF-8 编码的。
  为了与 Dart 代码兼容，十六进制编码的哈希值在 JavaScript 代码中也必须采用 UTF-8 编码。

以下 JavaScript 代码解决了这两个问题：

(async () => {

var spki = `-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEq6iOuQeIhlhywCjo5yoABGODOJRZ
c6/L8XzUYEsocCbc/JHiByGjuB3G9cSU2vUi1HUy5LsCtX2wlHSEObGVBw==
-----END PUBLIC KEY-----`; 
var pubkey = KEYUTIL.getKey(spki).getPublicKeyXYHex()
var pubkeyHex = '04' + pubkey.x + pubkey.y

var msgHashHex = ArrayBuffertohex(new TextEncoder().encode("bb5dbfcb5206282627254ab23397cda842b082696466f2563503f79a5dccf942").buffer)
// var msgHashHex = ArrayBuffertohex(new TextEncoder().encode("bb5dbfcb5206282627254ab23397cda8").buffer); // works also since only the first 32 bytes are considered for P-256

var sigHex = "3045022100f28c29042a6d766810e21f2c0a1839f93140989299cae1d37b49a454373659c802203d0967be0696686414fe2efed3a71bc1639d066ee127cfb7c0ad369521459d00"

var ec = new KJUR.crypto.ECDSA({'curve': 'secp256r1'})
var verified = ec.verifyHex(msgHashHex, sigHex, pubkeyHex)
console.log("Verification:", verified)
 
})();

<script src="https://cdnjs.cloudflare.com/ajax/libs/jsrsasign/10.4.0/jsrsasign-all-min.js"></script>

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