[Resource Topic] 2022/1739: On blindness of several ElGamal-type blind signatures

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On blindness of several ElGamal-type blind signatures

Authors: Alexandra Babueva, Liliya Akhmetzyanova, Evgeny Alekseev, Oleg Taraskin


Blind signature schemes are the essential element of many complex information systems such as e-cash and e-voting systems. They should provide two security properties: unforgeability and blindness. The former one is standard for all signature schemes and ensures that a valid signature can be generated only during the interaction with the secret signing key holder. The latter one is more specific for this class of signature schemes and means that there is no way to link a (message, signature) pair to the certain execution of the signing protocol. In the current paper we discuss the blindness property and various security notions formalizing this property. We analyze several ElGamal-type blind signature schemes regarding blindness. We present effective attacks violating blindness on three schemes. All the presented attacks may be performed by any external observer and do not require signing key knowledge. One of the schemes conceivably became broken due to an incorrect understanding of blindness property.

ePrint: https://eprint.iacr.org/2022/1739

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