MARK_BEGIN_LEN
if ((r = sshbuf_put(blob, MARK_BEGIN, MARK_BEGIN_LEN)) != 0 ||
if (encoded_len < (MARK_BEGIN_LEN + MARK_END_LEN) ||
memcmp(cp, MARK_BEGIN, MARK_BEGIN_LEN) != 0) {
cp += MARK_BEGIN_LEN;
encoded_len -= MARK_BEGIN_LEN;