WebCrypto GOST: Signature verification tool

GOST do not regulate the parameters of digital signature algorithms and hash functions. Different manufacturers use their sets. If the set is known, you can select otherwise enter the parameters of the algorithm manually.

In this example public key and singnature must be present as Big-endian Integer values. Some implementations of algorithm show data in machine Little-endian order - uses swap bytes button.

Preferably use a binary file, HEX or BASE64 encoding to verify the signature. The source plain text can be changed implicity, for example, because of the various options new line (CR, LFCR, CRLF) or char encoding mistmatch. In this case verification may fail.

// Decode data from source
function decode(ondata) {
    var format = fromtype.value.split('/');
    if (format[0] === 'Binary') { 
        var reader = new FileReader();
        reader.onload = function(e) {
            ondata(e.target.result);
        }
        reader.readAsArrayBuffer(fileSourceSelect.files[0]);
    } else {
        ondata(gostCrypto.coding[format[0]].decode(source.textContent, format[1]));
    }
}

// Verify signature
function verify(publicKey, signature, message) {
    var algorithm = {name: 'GOSTR3410'};

    // Set curve parameters
    if (namedCurve.value === 'Other') {
        algorithm.a = '0x' + paramA.value;
        algorithm.b = '0x' + paramB.value;
        algorithm.p = '0x' + paramP.value;
        algorithm.q = '0x' + paramQ.value;
        algorithm.x = '0x' + paramX.value;
        algorithm.y = '0x' + paramY.value;
    } else
        algorithm.namedCurve = namedCurve.value; 

    var modes = hashParam.value.split('/');
    algorithm.hash = {name: modes[0], sBox: modes[1]};

    // Get public key from trusted source
    gostCrypto.subtle.importKey('raw', publicKey,
            algorithm, true, ['verify']).then(function(key) {

        // Use public key for verify message signature
        return gostCrypto.subtle.verify(algorithm, key, signature, message);
    }).then(function(result) {

        // Check result
        verified.value = result ? 'Yes' : 'No';
    });
}

// Execute procedure
decode(function(message) {
    
    verify(gostCrypto.coding.Hex.decode(publicKey.value, 'BigEndian'), 
        gostCrypto.coding.Hex.decode(signature.value, 'BigEndian'), message);
});