Transform ASN. 1 signature to IEEE P1363 signature - ios

Question

I did generate a signature using the below code but, I want a signature in IEEE P1336 (length 80) format
guard let signData = SecKeyCreateSignature(
key,
SecKeyAlgorithm.ecdsaSignatureMessageX962SHA256,
signatureString.data(using: .utf8)! as CFData, &error) else {
let e = error!.takeRetainedValue() as Error
print("Signing Error \( e.localizedDescription)")
return nil
}
let signedData = signData as Data
let signedString = signedData.base64EncodedString(options: [])

Answer 1

I am not an expert in iOS. But I fixed this issue for a signature generated by iOS. You can create this format by your own. e.g. for SHA-256 hashed signature. JavaScript sample
function parseASN1ToIEEEP1363(signature) {
const buffer = new ArrayBuffer(signature.length);
const int8View = new Int8Array(buffer);
for (let i = 0, strLen = signature.length; i < strLen; i++) {
int8View[i] = signature.charCodeAt(i);
}
//Currently these bytes getting for SHA256. for other hashings need to make it dynamic
const r = new Int8Array(buffer.slice(4, 36));
const s = new Int8Array(buffer.slice(39));
return appendBuffer(r, s);
}
function appendBuffer(buffer1, buffer2) {
var tmp = new Uint8Array(buffer1.byteLength + buffer2.byteLength);
tmp.set(new Uint8Array(buffer1), 0);
tmp.set(new Uint8Array(buffer2), buffer1.byteLength);
return tmp;
};