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EUF-CMA and SUF-CMA – A Few Thoughts on Cryptographic Engineering

blog.cryptographyengineering.com · 393 words · saved by 1 readers

My academic website Mastodon Twitter Top Posts Useful crypto resources Bitcoin tipjar Cryptopals challenges Applied Cryptography Research: A Board Journal of Cryptographic Engineering (not related to this blog) There are two common formal definitions for the security of a digital signature scheme. Each of these definitions is presented as a “game”, or an experiment that is run between an attacker and some honest challenger. Informally, the EUF-CMA (Existential Unforgeability under Chosen Message Attack) experiment works like this: The scheme is considered secure if no (efficient) adversary has a non-negligible advantage in satisfying the conditions above. Normally the number of messages is bounded only by the attacker’s running time — however, for the special case of one-time signatures, the adversary is limited to asking for only one signature in step (2). This definition is fairly strong, but not as strong as possible. A slightly stronger definition is the SUF-CMA definition. Inform

There are two common formal definitions for the security of a digital signature scheme. Each of these definitions is presented as a “game”, or an experiment that is run between an attacker and some honest challenger. Informally, the EUF-CMA ( E xistential U n f orgeability under C hosen M essage A ttack) experiment works like this: The challenger generates a valid keypair ( ) and gives to the attacker. The attacker may now repeatedly ask for signatures on chosen messages ( ) of its choosing, and receives the valid signatures in response. Note that these queries and responses can be

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