How do sites like blockchain.info and bitaddress.org generate private keys by simply hashing a string? (the passphrase?)
In this wiki article, https://en.bitcoin.it/wiki/Technical_background_of_version_1_Bitcoin_addresses Step "0" starts with an ECDSA key pair already generated.
Does this mean that any 256-bit value can be a valid ECDSA private key? So wherever I am in the world, I can always just SHA256(passphrase) and get my private key?