Security researchers are warning that old Bitcoin addresses generated in the browser or through JavaScript-based wallet apps might be affected by a cryptographic flaw that allows attackers to brute-force private keys, take control of users' wallets, and steal funds.
The vulnerability resides in the use of the JavaScript SecureRandom() function for generating a random Bitcoin address and its adjacent private key (equivalent of a password).
SecureRandom() isn’t really random
The problem is that this function doesn't actually generate true random data, as an anonymous user recently
pointed out on the Linux Foundation mailing list, along with David Gerard, a UK-based Unix system administrator.
"It will generate cryptographic keys that, despite their length, have less than 48 bits of entropy, [...] so its output will have no more than 48 bits of entropy even if its seed has more than that,"
said Gerard.
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