Unforgeability. If all processes with identifier i are cor- rect and none of them performs Broadcast(m), then no correct process performs Accept(m, i).
Unforgeability. For all v and g, if Pi is honest and an honest party received (vki, sid, v, g) from π, then Pi invoked GradeGoss(sid, v). When a party receives (vk, sid, ⊥, g), we call this an equivocation proof for (vk, sid).
Unforgeability. Regarding forging Xxxxx's signcryption, a dishonest Xxx is in the best position to do so, as he is the only person who knows xb which is required to directly verify a signcrypted text from Xxxxx. In other words, the dishonest Xxx is the most powerful attacker we should look at. Given the signcrypted text (c; r; s) of a message m from Xxxxx, Xxx can use his private key xb to decrypt c and obtain m = Dk2 (c). Thus the original problem is reduced to one in which Xxx is in possession of (m; r; s). The latter is identical to the unforgeability of SDSS1 or SDSS2. As argued in Section 3, SDSS1 and SDSS2 are unforgeable. Therefore we conclude that both signcryption schemes SCS1 and SCS2 are unforgeable against adaptive attacks, under the assumption that the keyed hash function behaves like a random function.
Unforgeability. Informally, a scheme is unforgeable if no adversary can use signatures of a large majority of the honest parties on a message m and of a few honest parties on messages of its choice to forge an aggregated SRDS signature on a message other than m. { } ∈ ⊆ \ I | ∪ I| In a similar way to robustness, we consider an unforgeability game between a challenger and an adversary. The setup and corruption phase is identical to that in the robustness game. In the forgery challenge phase, the adversary chooses a set S [n] such that S < n/3 and messages m and mi i S. Given signatures of all honest parties outside of S on the message m and a signature of each honest party Pi in S on the message mi, the adversary outputs a signature σ. In the output phase, the challenger checks whether σ is a valid signature on a message different than m; if so the adversary wins. An SRDS scheme is unforgeable if no adversary can win the game except for negligible probability. Experiment Exptforge mode,Π,A (κ, n, t) The experiment Exptforge is a game between a challenger and the adversary A. The game is parametrized by an SRDS scheme Π and consists of the following phases:
Unforgeability. We define the strongest notion of unforgeability for a digital signature scheme, namely existential unforgeability under a chosen message attack [63]. This is defined via the following game between a challenger C and an adversary E. Initialization: C runs Setup on security parameter l to generate the public parameters params. C also runs KeyGen to obtain a public key PK and a private key SK. C gives the parameters params and the public key PK to E. Sign: E may request a signature on any message m. C computes σ=Sign(m, SK), and gives σ to E. Output: E outputs a signature σ∗ and a message m∗. E wins the game if Verify(m∗, PK, σ∗) outputs accept, and no previous Sign query was made on m∗.
Unforgeability. Unforgeability ensures that no-one other than a ring member can create a valid ring sig- nature for that ring. Unforgeability is defined via the following game between a challenger C and an adversary E.
Unforgeability. Unforgeability of an NIDV undeniable signature scheme is defined via the following game between a challenger C and an adversary E:
Unforgeability. Unforgeability of a DV signature scheme is defined via the following game between a challenger C and an adversary E:
Unforgeability. Informally, a scheme is unforgeable if no adversary can use signatures of a large majority of the honest parties on a message m and of a few honest parties on messages of its choice to forge an aggregated SRDS signature on a message other than m. In a similar way to robustness, we consider an unforgeability game between a challenger and an adversary. The setup and corruption phase is identical to that in the robustness game. In the forgery challenge phase, the adversary chooses a set S ⊆ [n] \ I such that |S ∪ I| < n/3 and messages m and {mi}i∈S. Given signatures of all honest parties outside of S on the message m and a signature of each honest party Pi in S on the message mi, the adversary outputs a signature
