Freshness. With respect to Custom Components, Supplier will notify EMS Provider and the Cisco Entities in the event any such Component has remained in any Hub for more than [****] (the “Freshness Period”). Upon receipt of such notice, EMS Provider will, within two business days, issue a Pull Signal to Hub Operator with respect to such Component, subject to the following exceptions:
Freshness. The freshness notion captures the intuitive fact that a session key is not “obviously” known to the adversary. A device U is said to be Fresh, in the current operation execution, (or holds a Fresh sk) if the following two conditions are satisfied. First, nobody in has ever been asked for a Corrupt-query from the beginning of the game (during the lifetime of the αi’s). Second, in the current operation execution, U has accepted and neither U nor its partners (other parties with the same session key) have been asked for a Reveal-query. A A A
Freshness a Goods intending to be sold at the market must be of top quality. Inferior product will not be tolerated as it goes against everything the market represents, that is – Quality, Fresh Gisborne Produce. Second grade produce, if sold must be clearly marked as such. If selling second grade produce, first grade produce must also be present for sale.
Freshness. The milk must be less than three days old at the time of delivery.
Freshness. As mentioned above, the query Test(Ui) can be asked only when user Ui is fresh. We say that a user Ui is fresh in the current protocol execution if all the following conditions hold: (1) ACCi = TRUE, (2) no one in PIDi has been asked for a Reveal query (note that Ui ∈ PIDi unless PIDi =/ the initialization phase. ∅), and (3) no one in U has ever been asked for a Corrupt query since 4 Security Definitions In this section we first define what it means to securely distribute a session key within the security model given above and then explore the underlying assumptions on which the security of our scheme rests. Authenticated Group Key Agreement. The security of an authenticated group key agreement scheme P is defined in the following context. The adversary A, equipped with all the queries described in the security model, executes the protocols IKA1, LP1, and JP1 as many times as she wishes in an arbitrary order, of course, with IKA1 being the first one executed. During executions of the protocols, the adversary A, at any time, asks a Test query to a fresh user, gets back an ℓ-bit string as the response to this query, and at some later point in time, outputs a bit b′ as a guess for the secret bit b. Let GG (Good Guess) be the event that the adversary A correctly guesses the bit b, i.e., the event that b′ = b. Then we define the advantage of A in attacking P as P AdvA(k) = 2 · Pr[GG] − 1. P We say that a group key agreement scheme P is secure if AdvA(k) is negligible for any prob- abilistic polynomial time adversary A. Secure Signature Schemes. We review here the standard definition of a digital signa- ture scheme. A digital signature scheme Γ = (G, S, V) is defined by the following triple of algorithms: • A probabilistic key generation algorithm G, on input 1k, outputs a pair of matching public and private keys (PK, SK). • A signing algorithm S is a (possibly probabilistic) polynomial time algorithm that, given a message m and a key pair (PK, SK) as inputs, outputs a signature σ of m. • A verification algorithm V is a (usually deterministic) polynomial time algorithm that on input (m, σ, PK), outputs 1 if σ is a valid signature of the message m with respect to PK, and 0 otherwise. Γ Γ Γ We denote by XxxxX(k) the probability of an adversary A succeeding with an existential forgery under adaptive chosen message attack [20]. We say that a signature scheme Γ is secure if SuccA(k) is negligible for any probabilistic polynomial time adversary A. We denote by SuccΓ(t...
Freshness. An instance Πıi is fresh if before the adversary answers the Test oracle, neither the instancUei Πıi nor anyone of its partnered instances has received a Dk-Reveal query. Ui Let us proceed to the main security notion of GKAs against passive attackers. In the conventional GKA definitions, the group members finally share a secret key. Accordingly, the security is defined by the indistinguishability of the shared key from a random string. In our definition we allow the group members to have different decryption keys. Hence, we define the security of GKAs by the security of the final confidential channel, i.e., the indistinguishability of messages transferred via this channel.
Freshness. Session 𝗌 is fresh if the adversary issues queries of 𝑆𝐾𝑅𝑒𝑣𝑒𝑎𝑙(𝐷𝑒𝑣), 𝐸𝑝ℎ𝑅𝑒𝑣𝑒𝑎𝑙(𝐷𝑒𝑣), 𝐶𝑜𝑟𝑟𝑢𝑝𝑡(𝐷𝑒𝑣), and 𝐶𝑜𝑚𝑝𝑟𝑜𝑚𝑖𝑠��(𝐷𝑒��) while it or its matching session is at risk. These queries need to be requested before 𝑆𝐾𝑖𝑗 expires. This is to distinguish fresh and random session keys. 𝑛 Definition 4. (Difference lemma). Suppose 𝑆𝑢𝑐𝑐 𝒜| 𝑛 = 1, 2, 3 denote the event in probability density function and 𝑆𝑢𝑐𝑐 𝒜 𝖠 ¬ 𝑆𝑢𝑐𝑐 𝒜 ⇔ 𝑆𝑢𝑐𝑐 𝒜 𝖠 ¬ 𝑆𝑢𝑐𝑐 𝒜. Then we have |Pr[𝑆𝑢𝑐𝑐 𝒜] − Pr[𝑆𝑢𝑐𝑐 𝒜]| ≤ Pr[𝑆𝑢𝑐𝑐 𝒜]. The adversary can request the following queries to breach semantic security of the proposed protocol. 𝑖 𝑺𝒆𝒏𝒅(𝑫𝒆𝒗𝒊, 𝑫𝒆𝒗𝒋, < 𝒎𝟏 >). Once this query is implemented, 𝒜 transmits the message 𝑚1 =< 𝐴𝐼𝐷𝑖 , 𝑍𝑖 , 𝜏𝑖 , 𝑡1 > instead of 𝐷𝑒𝑣𝑖 to 𝐷𝑒𝑣𝑗. 𝐷𝑒𝑣𝑗 checks for validity of the query and, as specified above (see sec 4.2.3), calculates the session key 𝑆𝐾𝑗 = ℎ(𝑇𝐼𝐷′ ∥ 𝑇𝐼𝐷𝑗 ∥ 𝐾𝑗 ∥ 𝑡2) and returns the message < 𝐴𝐼𝐷𝑗 , 𝑍𝑗 , 𝜏𝑗 , 𝑡2 > . 𝑗 𝑺𝒆𝒏𝒅(𝑫𝒆𝒗𝒋, 𝑫𝒆𝒗𝒊, < 𝒎𝟐 >). 𝒜 sends the message 𝑚2 =< 𝐴𝐼𝐷𝑗 , 𝑍𝑗, 𝜏𝑗 , 𝑡2 > to 𝐷𝑒𝑣𝑖 to forge the oracle 𝐷𝑒𝑣𝑗. upon receiving the message, 𝐷𝑒𝑣𝑖checks for values of the query and, as specified above, calculates the session key 𝑆𝐾𝑖 = ℎ(𝑇𝐼𝐷𝑖 ∥ 𝑇𝐼𝐷′ ∥ 𝐾𝑖 ∥ 𝑡2) and completes the session. If the conditions are not met or the session expires, the query is rejected. 𝑬𝒙𝒆𝒄𝒖𝒕𝒆(𝑫𝒆𝒗). For this query, 𝒜 obtains < 𝑚1 > and < 𝑚2 > in authentication and key agreement phase. It is like a passive eavesdropping attack. 𝑯𝒂𝒔𝒉(𝑽𝒂𝒓). The oracle 𝐷𝑒𝑣 generates a list 𝐿𝐻 to store hash records. When the adversary issues 𝐻𝑎𝑠ℎ(𝑉𝑎𝑟), 𝐷𝑒𝑣 searches in the list 𝐿𝐻 and returns the corresponding 𝑣 in tuple (𝑉𝑎𝑟,𝑣). Otherwise, it generates a random value 𝑣′ and adds (𝑉𝑎𝑟,𝑣′) to its list, returning the 𝑣′. 𝑺𝑲𝑹𝒆𝒗𝒆𝒂𝒍(𝑫𝒆𝒗). It simulates session key leakage by the adversary. If 𝑆𝐾𝑖𝑗 is generated, 𝐷𝑒𝑣 returns it in response to the query. Otherwise, it returns 𝑛𝑢𝑙𝑙. 𝑬𝒑𝒉𝑹𝒆𝒗𝒆𝒂𝒍(𝑫𝒆𝒗𝒊). 𝒜 uses this query to obtain ephemeral secret parameters 𝛼 and 𝑥 of 𝐷𝑒��𝑖 to perform ephemeral secret leakage attack. 𝑪𝒐𝒓𝒓𝒖𝒑𝒕(𝑫𝒆𝒗𝒊). By running this query, the adversary obtains long-static secret parameters 𝑑𝑖 and 𝑀𝑖 of 𝐷𝑒𝑣𝑖. ��𝒐𝒎𝒑𝒓𝒐��𝒊𝒔𝒆(𝑫𝒆𝒗𝒊). By querying this, all static and dynamic secret parameters of 𝐷𝑒𝑣�...
Freshness. Freshness is defined in Definition 5. U1
Freshness. A Test-query should only be allowed to those instances holding a key that is not for trivial reasons known to the adversary. To this aim, an instance Πsi is called fresh if none of the following two conditions hold: – For some Uj ∈ pidsi a Corrupt(Uj) query was executed before a query of the form Send(Uk, sk, ∗) has taken place where Uk ∈ pidsi . – The adversary queried Reveal(U ,s ) with Πsi and i sj being partnered.
Freshness. Two notions of freshness are defined to ensure that a session key is not disclosed to the adversary and to incorporate a requirement for forward secrecy [3, 26]. – An instance Ui is nfs-fresh (fresh with no requirement for forward secrecy) unless either
