Niko's Project Corner

Hash-based commitment schemes without a computer

An in­ter­est­ing ques­tion was posted to crypto.stack­ex­change.com: "Is there a sim­ple hash func­tion that one can com­pute with­out a com­puter?" Here are three pro­posed al­go­rithms based on Zo­brist hash­ing, RC4 and A5/1. These should be reasonably secure even against attacks with a calculator, except the one based on Zobrist hashing (but I don't know how to prove or dis-prove this claim). These constructs are especially well suited for com­mit­ment schemes.

Anonymous and secure information storing and sharing

Nowa­days en­cryp­tion is stan­dard prac­tice on web when data is in tran­si­tion, and there are even a few ser­vices which of­fer client-side en­cryp­tion and thus are truly end-to-end. Nev­er­the­less for some rea­son they all re­quire you to cre­ate and ac­count by pro­vid­ing your email and pass­word, al­though this is not strictly nec­es­sary for stor­ing and shar­ing data. In this sys­tem the doc­ument id, en­cryp­tion key and HMAC key are gen­er­ated ad-hoc on the client and only min­imal nec­es­sary in­for­ma­tion is re­vealed to the server. A live demo should be avail­able at no­knowl­edgenotes.nikonyrh.org.

Cheap off-site backup at Amazon Glacier

In ad­di­tion to a mir­rored and check-summed ZFS based backup server, I wanted to have back­ups out­side by premises to be safer against haz­ards such as bur­glary, fire and wa­ter dam­age. ZFS can al­ready re­sist sin­gle disk fail­ure and can re­pair silent data cor­rup­tion, but for im­por­tant mem­ories that isn't suf­fi­cient level of pro­tec­tion. My ever-grow­ing data set is cur­rently 150k files, hav­ing a to­tal size of 520 Gb. Ama­zon's Glacier seems to be the most cost ef­fi­cient so­lu­tion with so­phis­ti­cated APIs and SDKs.