An anonymous reader quotes a report from Ars Technica: A crippling flaw affecting millions -- and possibly hundreds of millions -- of encryption keys used in some of the highest-stakes security settings is considerably easier to exploit than originally reported, cryptographers declared over the weekend. The assessment came as Estonia abruptly suspended 760,000 national ID cards used for voting, filing taxes, and encrypting sensitive documents. The critical weakness allows attackers to calculate the private portion of any vulnerable key using nothing more than the corresponding public portion. Hackers can then use the private key to impersonate key owners, decrypt sensitive data, sneak malicious code into digitally signed software, and bypass protections that prevent accessing or tampering with stolen PCs. When researchers first disclosed the flaw three weeks ago, they estimated it would cost an attacker renting time on a commercial cloud service an average of $38 and 25 minutes to break a vulnerable 1024-bit key and $20,000 and nine days for a 2048-bit key. Organizations known to use keys vulnerable to ROCA—named for the Return of the Coppersmith Attack the factorization method is based on—have largely downplayed the severity of the weakness.
On Sunday, researchers Daniel J. Bernstein and Tanja Lange reported they developed an attack that was 25 percent more efficient than the one created by original ROCA researchers. The new attack was solely the result of Bernstein and Lange based only on the public disclosure information from October 16, which at the time omitted specifics of the factorization attack in an attempt to
increase the time hackers would need to carry out real-world attacks. After creating their more efficient attack, they submitted it to the original researchers. The release last week of the original attack may help to improve attacks further and to stoke additional improvements from other researchers as well.
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