antelope-webauthn/_utils/decode-der.js

A WebAuthn.io crypto utility for generating signatures, creating public keys, and verifying them, designed for Antelope-based blockchains such as Vaulta, WAX, and other related platforms. This package provides convenient tools to handle key pair generatio

/**
 * Extracts the s and r signatures from a der encoded signature
 */
export default function decodeDER(der) {
    if (der[0] !== 0x30)
        throw new Error("Expected der encoded signature to start with 0x30");
    if (der[2] !== 0x02)
        throw new Error("Expected 3rd byte of der encoded signature to be 0x02 indicating a number");
    const length_of_sig = der[1];
    const r_len = der[3];
    const r = der.slice(4, 4 + r_len);
    const [int_0x02] = der.slice(4 + r_len, 5 + r_len);
    if (int_0x02 !== 0x02)
        throw new Error("Invalid DER Encoded signature");
    const s_len_pos = 5 + r_len;
    const [s_length] = der.slice(s_len_pos, s_len_pos + 1);
    if (Number(r_len) + Number(s_length) + 4 !== length_of_sig)
        throw new Error("Invalid DER signature length");
    const s = der.slice(s_len_pos + 1, s_len_pos + s_length + 1);
    return {
        r: r[0] ? r : r.slice(1),
        s: s[0] ? s : s.slice(1),
    };
}