Mihir Bellare

Mihir Bellare is a prominent computer scientist known for his contributions to the fields of cryptography and information security. He is particularly recognized for his work on the theoretical foundations of cryptographic protocols and algorithms. Bellare has made significant advancements in understanding the security of cryptographic primitives, including digital signatures, hash functions, and encryption schemes.

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Mihir Bellare is a computer scientist whose work in cryptography connects practical constructions with provable security: a claimed security property is expressed as a mathematical condition, with a proof relating an attack to specified assumptions. His UC San Diego homepage describes this emphasis on primitives of applied interest.

With Ran Canetti and Hugo Krawczyk, Mihir Bellare developed the hash-based message authentication code HMAC. Their 1996 paper studies how to turn an unkeyed cryptographic hash function into a keyed message authentication mechanism and analyzes the resulting construction under explicit assumptions. The practical task is to let two parties sharing a cryptographic key detect unauthorized message changes: an ordinary public hash function alone cannot prevent an attacker from changing a message and recomputing its hash.^[ref] The construction was subsequently specified in the February1997 document HMAC: Keyed-Hashing for Message Authentication (RFC 2104); that RFC is explicitly categorized as Informational.^[ref]

With Oded Goldreich, Mihir Bellare also refined the definition of a proof of knowledge. Their work makes “knowing” a mathematical witness operational through a knowledge extractor, with a knowledge error distinguishing acceptance obtainable without such knowledge from acceptance that supports extraction.^[ref]

The graph isomorphism example makes that distinction concrete. A prover sends a graph

H

and must answer a random challenge asking for an isomorphism from either

G_{1}

G_{2}

H

. Preparing only one answer can give acceptance probability

1/2

, so one accepted exchange is not itself evidence that the prover knows an isomorphism between

G_{1}

and

G_{2}

. If an extractor obtains valid maps

π_{1} : G_{1} \to H

and

π_{2} : G_{2} \to H

for the same

H

, it can construct

π_{2}^{- 1} \circ π_{1} : G_{1} \to G_{2}

. This illustrates why a careful extraction definition, rather than the informal phrase “the verifier was convinced”, matters when building larger cryptographic protocols.^[ref]