sha512_blocks
sha512_blocks(&ctx->state, ctx->buf, 1);
sha512_blocks(&ctx->state, data, nblocks);
sha512_blocks(&ctx->state, ctx->buf, 1);
sha512_blocks(&ctx->state, ctx->buf, 1);
sha512_blocks(istate, derived_key.b, 1);
sha512_blocks(ostate, derived_key.b, 1);
sha512_blocks(&ctx->ostate, ctx->sha_ctx.buf, 1);