I'm currently using the lightwallet.js for ethereum and it seems to only accept a mnemonic seed to generate an ethereum address. I want to be able to use my Bitcoin private key to generate an ethereum address. I'm able to generate a bitcoin private key using bitcoinjs library, but I can't seem to figure out how I can do this with ethereum using a bitcoin private key. Is there a specific library I need to use?
A private key in both bitcoin and ethereum is simply a random 256 bit number (actually a number between 0 and the order of the secp256k1 curve, but that's not really important).
If you can get your raw bitcoin public key, i.e.something like a random hex string of length 64, then it can be used directly as a raw ETH private key in any library or client.
For example, to import it into geth just use
geth account import <(my_privkey)
for parity see How to import a plain private key into Parity?
You can even use openssl, see https://kobl.one/blog/create-full-ethereum-keypair-and-address/
Putting a bitcoin private key into my ether wallet as a private key will open an Ethereum wallet
I’m not sure how this works
This also makes a few valid Ethereum addresses