Quote from: Lacrim on Today at 01:21:11 PM

Hi. Is there any library or even third party API that allows to initiate a transaction and send funds just by using private keys? I want a lightweight solution that doesn't require running a full node or downloading the blockchain.

I've seen today a topic about an open source web wallet that doesn't need local blockchain: https://bitcointalk.org/index.php?topic=5392903.0
It does calls to various servers and block explorers to do the job, so privacy is zero.

It's a HD wallet, so it works based on a seed, not PK. But it's open source; I don't know, it may be close enough to what you need, at least as source of inspiration.