Published on March 31, 2014
Securing your Bitcoins Kitten Tofu
Hello! • Kitten Tofu! • Cryptocurrency enthusiast since 2011! • Worked in infosec for a couple years! • Full time cryptocurrency researcher! !
This Talk I want you to interrupt me.!
This Talk • Entropy! • Use Cases and Adversaries! • blockchain.info client! • Ofﬂine Wallets! • m of n signature schemes! • BIP32 (“HDWallets”)! • Network Architecture!
Entropy • Measure of “randomness”! • Usually expressed as the number of bits! ! • Pick truly random passphrases! • Google for “diceware”!
Use cases + Adversaries • Short Term / Easy Access / “hot wallet”! • Long Term / Savings / “cold storage”! ! • Somebody who has physical access to you! • Some random hacker on the internet!
Offline Wallets • Private keys on an air gapped computer! Ofﬂine Computer! Online Computer! ernet! Private Keys
Offline Wallets • Private keys on an air gapped computer! Ofﬂine Computer! Online Computer! ernet! Public Keys! Private Keys
Offline Wallets • Private keys on an air gapped computer! Ofﬂine Computer! Online Computer! ernet! Public Keys! Private Keys Unsigned! Transaction!
Offline Wallets • Private keys on an air gapped computer! Ofﬂine Computer! Online Computer! ernet! Public Keys! Private Keys Signed! Transaction!
Offline Wallets Armory makes this easy!
Offline Wallets • Encrypt properly! ! • Watch out for USB viruses!!
transactions • BIP 11, Gavin Andresen! • blockchain.info implements this! • DIY: Shamir’s secret sharing scheme! • Good for shared accounts! • Mitigation against losing access!
BIP32 - HD Wallets • Create two “extended keys”! • One for public keys! • One for private keys! • Child Key Derivation (CKD)! • Given one of these extended keys, you can derive any of 232 -1 “children”!
BIP32 - HD Wallets
Architecture • Online gambling website / exchange! • Online shop!
Architecture Web Server! Hot Wallet! ernet! Cold WallManually processing Private Key Generator! Public Key! Generator! Private Ke
Architecture Web Server! ernet! Cold WallManually processing Public Key! Generator! Private Ke
Malleability • Your exact transactions are not the only transactions that can spend your funds! ! • Not as bad as it sounds, just don’t rely on your txids making it into the blockchain!
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