void privkey_sign(struct peer *peer, const void *src, size_t len,
struct signature *sig)
{
struct sha256_double h;
sha256_double(&h, memcheck(src, len), len);
sign_hash(peer->dstate->secpctx,
&peer->dstate->secret->privkey, &h, sig);
}
void base58_get_checksum(u8 csum[4], const u8 buf[], size_t buflen)
{
struct sha256_double sha_result;
/* Form checksum, using double SHA2 (as per bitcoin standard) */
sha256_double(&sha_result, buf, buflen);
/* Use first four bytes of that as the checksum. */
memcpy(csum, sha_result.sha.u.u8, 4);
}