Cbor.js

const cbor = require('cbor');

// Example base64-encoded attestation object (replace with your actual data)
const base64AttestationObject = "your_base64_encoded_attestation_object";

// Decode the Base64 string into a buffer
const attestationBuffer = Buffer.from(base64AttestationObject, 'base64');

// Decode the CBOR object
cbor.decodeFirst(attestationBuffer)
    .then((decoded) => {
        console.log("Decoded Attestation Object:", decoded);

        // Extract the fields
        const fmt = decoded.fmt; // Attestation format
        const authData = decoded.authData; // Authenticator data
        const attStmt = decoded.attStmt; // Attestation statement

        console.log("Format (fmt):", fmt);
        console.log("Authenticator Data (authData):", authData.toString('hex'));

        if (attStmt) {
            console.log("Attestation Statement (attStmt):", attStmt);

            // Handle x5c (attestation certificate chain)
            if (attStmt.x5c) {
                const certificates = attStmt.x5c.map(cert => cert.toString('hex'));
                console.log("Certificates (x5c):", certificates);
            }

            // Handle signature (sig)
            if (attStmt.sig) {
                console.log("Signature (sig):", attStmt.sig.toString('hex'));
            }
        }

        // Parse the authData field for more details
        parseAuthData(authData);
    })
    .catch((err) => {
        console.error("Failed to decode CBOR:", err);
    });

// Function to parse the authData field
function parseAuthData(authData) {
    if (!authData || authData.length < 37) {
        console.error("authData is invalid or too short");
        return;
    }

    // RP ID hash (first 32 bytes)
    const rpIdHash = authData.slice(0, 32);
    console.log("RP ID Hash:", rpIdHash.toString('hex'));

    // Flags (1 byte after RP ID hash)
    const flags = authData[32];
    console.log("Flags:", flags.toString(16));

    // Sign count (4 bytes after flags)
    const signCount = authData.readUInt32BE(33);
    console.log("Sign Count:", signCount);

    // Handle attested credential data if present (flag bit 6)
    if (flags & 0x40) {
        // AAGUID (16 bytes after RP ID hash and flags)
        const aaguid = authData.slice(37, 53);
        console.log("AAGUID:", aaguid.toString('hex'));

        // Credential ID length (2 bytes after AAGUID)
        const credentialIdLength = authData.readUInt16BE(53);
        console.log("Credential ID Length:", credentialIdLength);

        // Credential ID (variable length)
        const credentialIdStart = 55;
        const credentialIdEnd = credentialIdStart + credentialIdLength;
        const credentialId = authData.slice(credentialIdStart, credentialIdEnd);
        console.log("Credential ID:", credentialId.toString('hex'));

        // Public key (CBOR-encoded, starts after Credential ID)
        const publicKeyData = authData.slice(credentialIdEnd);
        console.log("Public Key (CBOR):", publicKeyData.toString('hex'));

        // Decode the CBOR-encoded public key
        cbor.decodeFirst(publicKeyData)
            .then((publicKey) => {
                console.log("Decoded Public Key:", publicKey);
            })
            .catch((err) => {
                console.error("Failed to decode public key CBOR:", err);
            });
    }
}