{"id":283892,"date":"2016-02-26T11:40:41","date_gmt":"2016-02-26T19:40:41","guid":{"rendered":"https:\/\/www.microsoft.com\/en-us\/research\/?post_type=msr-research-item&#038;p=283892"},"modified":"2016-08-29T08:33:58","modified_gmt":"2016-08-29T15:33:58","slug":"charles-river-crypto-day-three-round-non-malleable-commitment-non-malleable-codes","status":"publish","type":"msr-video","link":"https:\/\/www.microsoft.com\/en-us\/research\/video\/charles-river-crypto-day-three-round-non-malleable-commitment-non-malleable-codes\/","title":{"rendered":"Charles River Crypto Day: Three-Round Non-Malleable Commitment from Non-Malleable Codes"},"content":{"rendered":"<p>We present a new non-malleable commitment protocol. Our protocol has the following features:<\/p>\n<ul>\n<li>The protocol has only <em>three rounds<\/em> of interaction. Pass (TCC 2013) showed an impossibility result for a two-round non-malleable commitment scheme w.r.t. a black-box reduction to any \u201cstandard\u201d intractability reduction. Thus, this resolves the round complexity of non-malleable commitment at least w.r.t. black-box security reductions. Our construction is secure as per the standard notion of non-malleability w.r.t. commitment.<\/li>\n<li>Our protocol is <em>truly\u00a0efficient<\/em>. In our basic protocol, the entire computation of the committer is dominated by just three invocations of a non-interactive statically binding commitment scheme, while, the receiver computation (in the commitment stage) is limited to just sampling a random string. Unlike many previous works, we directly construct a protocol for large tags and hence avoid any non-malleability amplification steps.<\/li>\n<li>Our protocol is based on a black-box use of any non-interactive statistically binding commitment scheme. Such schemes, in turn, can be based on any one-to-one one-way function (or any one-way function at the cost of an extra initialization round). Previously, the best known black-box construction of non-malleable commitments required a larger (constant) number of rounds.<\/li>\n<li>Our construction is public-coin and makes use of only black-box simulation. Prior to our work, no public-coin constant round non-malleable commitment schemes were known based on black-box simulation.<\/li>\n<\/ul>\n<p>Our techniques depart <em>significantly<\/em> from the techniques used previously to construct non-malleable commitment schemes. As a main technical tool, we rely on non-malleable codes in the split state model. Our proofs of security are purely combinatorial in nature.<\/p>\n<p>In addition, we also present a simple construction of constant round non-malleable commitments from any one-way function. While this result is not new, the main feature is its simplicity compared to any previous construction of non-malleable commitments (regardless of the number of rounds). We believe the construction is simple enough to be covered in a graduate level course on cryptography. The construction uses non-malleable codes in the split state model in a black-box way. This is joint work with Vipul Goyal and Omkant Pandey.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>We present a new non-malleable commitment protocol. Our protocol has the following features: The protocol has only three rounds of interaction. Pass (TCC 2013) showed an impossibility result for a two-round non-malleable commitment scheme w.r.t. a black-box reduction to any \u201cstandard\u201d intractability reduction. Thus, this resolves the round complexity of non-malleable commitment at least w.r.t. 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