subKeysOrderedByEncryptionPriority.js

/**
 * Returns an array containing all the given Key's subkeys sorted in prefered
 * order for encryption.
 *
 * The prefered order is as follow:
 * - First all the one-time keys sorted by their expiration time (closest to
 *   expiration first).
 * - Then all the non one-time keys sorted by their creation time (more
 *   recently created first).
 *
 * @param  {key/key} the OpenPGP key.
 * @returns {Array<module:key/SubKey>}
 */
export async function subKeysOrderedByEncryptionPriority(key, date = new Date()) {
    const toComparable = async subKey => ({
        isOneTimeKey: await subKey.isOneTimeKey(key.keyPacket, date),
        expire: await subKey.getExpirationTime(key.keyPacket, date),
        created: subKey.keyPacket.created,
        key: subKey
    });
    const fromComparable = obj => obj.key;
    const comparableSubKeys = await Promise.all(key.getSubkeys().map(toComparable));
    comparableSubKeys.sort((a, b) => {
        if (!a.isOneTimeKey && !b.isOneTimeKey) {
            /* last created key first */
            return b.created - a.created;
        } else if (a.isOneTimeKey && !b.isOneTimeKey) {
            /* a first as it is a one-time key */
            return -1;
        } else if (b.isOneTimeKey && !a.isOneTimeKey) {
            /* b first as it is a one-time key */
            return 1;
        } else if (a.expire && b.expire) {
            /* both a and b are one-time key, we put first the one closest to its
expiration according to draft-brown-pgp-pfs-03 §2.1 */
            return a.expire - b.expire;
        } else { // one of the key has expired or is invalid.
            /* last created key first */
            return b.created - a.created;
        }
    });
    return comparableSubKeys.map(fromComparable);
}