derEncodeECDSASignatureToUinit8Array.js

function derEncodeECDSASignatureToUinit8Array(signatureUint8Array) {
    let out_sigder = new ArrayBuffer(72);
    let out_sigder_DV = new DataView(out_sigder);
    let out_sigder_BA = new Uint8Array(out_sigder);

    // Need to caress into dumb der format ..
    let i;
    let lead_s = 0;  // leading zeros
    let lead_r = 0;

    for (i = 0; i < 32; i++)
        if (signatureUint8Array[i] === 0) lead_r++;
        else break;

    for (i = 0; i < 32; i++)
        if (signatureUint8Array[i + 32] === 0) lead_s++;
        else break;

    let pad_s = ((signatureUint8Array[32 + lead_s] & 0x80) === 0x80) ? 1 : 0;
    let pad_r = ((signatureUint8Array[0 + lead_r] & 0x80) === 0x80) ? 1 : 0;
    out_sigder_DV.setUint8(0, 0x30);
    out_sigder_DV.setUint8(1, 0x44 + pad_s + pad_r - lead_s - lead_r);

    // R ingredient
    out_sigder_DV.setUint8(2, 0x02);
    out_sigder_DV.setUint8(3 + pad_r, 0);
    out_sigder_DV.setUint8(3, 0x20 + pad_r - lead_r);
    let startR = lead_r;
    let numberOfBytesToCopyR = 32 - lead_r;
    let endR = startR + numberOfBytesToCopyR;
    out_sigder_BA.set(signatureUint8Array.slice(startR, endR), 4 + pad_r);

    // S ingredient
    out_sigder_DV.setUint8(4 + 32 + pad_r - lead_r, 0x02);
    out_sigder_DV.setUint8(5 + 32 + pad_r + pad_s - lead_r, 0);
    out_sigder_DV.setUint8(5 + 32 + pad_r - lead_r, 0x20 + pad_s - lead_s);
    let startS = 32 + lead_s;
    let numberOfBytesToCopyS = 32 - lead_s;
    let endS = startS + numberOfBytesToCopyS;
    out_sigder_BA.set(signatureUint8Array.slice(startS, endS), 6 + 32 + pad_r + pad_s - lead_r);

    return out_sigder_BA.slice(0, 0x46 + pad_s + pad_r - lead_r - lead_s);
}