Barnum, Crepeau, Gottesman, Tapp, and Smith (quant-ph 0205128) proposed methods for authentication of quantum messages. The first method is an interactive protocol (TQA') based on teleportation. The second method is a noninteractive protocol (QA) in which the sender first encrypts the message using a protocol QEnc and then encodes the quantum ciphertext with an error correcting code chosen secretly from a set (a purity test code (PTC)). Encryption was shown to be necessary for authentication. We augment the protocol QA with an extra step which recycles the entire encryption key provided QA accepts the message. We analyze the resulting integrated protocol for quantum authentication and key generation, which we call QA+KG. Our main result is a proof that QA+KG is universal composably (UC) secure in the Ben-Or-Mayers model (quant-ph 0409062). More specifically, this implies the UC-security of (a) QA, (b) recycling of the encryption key in QA, and (c) key-recycling of the encryption scheme QEnc by appending PTC. For an m-qubit message, encryption requires 2m bits of key; but PTC can be performed using only O(log m) + O(log e) bits of key for probability of failure e. Thus, we reduce the key required for both QA and QEnc, from linear to logarithmic net consumption, at the expense of one bit of back communication which can happen any time after the conclusion of QA and before reusing the key. UC-security of QA also extends security to settings not obvious from quant-ph 0205128. Our security proof structure is inspired by and similar to that of quant-ph 0205128, reducing the security of QA to that of TQA'. In the process, we define UC-secure entanglement, and prove the UC-security of the entanglement generating protocol given in quant-ph 0205128, which could be of independent interest.
One feature that slightly distinguishes @cite_0 @cite_38 from ours is that they demonstrate that the entire key can be recycled whereas we sacrifice a vanishing fraction of the key. While interesting theoretically, the distinction is not practically important because, in our case, additional key to make up for the small loss can be added to the message with negligible additional cost. Furthermore, some of the schemes that allow total key recycling require substantially more initial key (while QA is key-optimal up to an additive logarithmic amount, which we believe can be reduced to a constant in view of results in @cite_6 ).
@cite_0 @cite_38 @cite_6
110254507 2006333615 2547753369 2143174824
In this paper, we examine the potential of using a thermal camera to recover codes typed into keypads in a variety of scenarios. This attack has the advantage over using a conventional camera that the codes do not need to be captured while they are being typed and can instead be recovered for a short period afterwards. To get the broadest sense of how effective such an attack might be, we consider a number of variables: the material of the keypad, the user entering the code, the distance from the camera to the keypad, and the possible methods used to analyze the data. First, we present code recovery results from human review of our test data set; this provides us with a baseline for the overall effectiveness of thermal camera-based attacks. Second, using techniques from computer vision we automatically extract the code from raw camera data, thus demonstrating that this attack has the potential to scale well in practice. As we will see, both human and automated attacks are by and large successful in recovering the keys present in the code, even a full minute after they have been pressed; both methods are also able to determine the exact code (i.e., including the order in which the keys were pressed) for a smaller fraction of codes. Even without ordering, however, the search space of possible keys is still vastly reduced by knowing the keys pressed; for example, the search space is reduced from 10,000 possible codes to approximately 24 for a 4-digit code. In large-scale attacks involving many unique codes, such as on ATM PINs, our success rate indicates that an adversary can correctly recover enough codes to make such an attack economically viable. We consider the secret key generation problem when sources are randomly excited by the sender and there is a noiseless public discussion channel. Our setting is thus similar to recent works on channels with action-dependent states where the channel state may be influenced by some of the parties involved. We derive single-letter expressions for the secret key capacity through a type of source emulation analysis. We also derive lower bounds on the achievable reliability and secrecy exponents, i.e., the exponential rates of decay of the probability of decoding error and of the information leakage. These exponents allow us to determine a set of strongly-achievable secret key rates. For degraded eavesdroppers the maximum strongly-achievable rate equals the secret key capacity; our exponents can also be specialized to previously known results. In deriving our strong achievability results we introduce a coding scheme that combines wiretap coding (to excite the channel) and key extraction (to distill keys from residual randomness). The secret key capacity is naturally seen to be a combination of both source- and channel-type randomness. Through examples we illustrate a fundamental interplay between the portion of the secret key rate due to each type of randomness. We also illustrate inherent tradeoffs between the achievable reliability and secrecy exponents. Our new scheme also naturally accommodates rate limits on the public discussion. We show that under rate constraints we are able to achieve larger rates than those that can be attained through a pure source emulation strategy. Barnum, Crepeau, Gottesman, Tapp, and Smith (quant-ph 0205128) proposed methods for authentication of quantum messages. The first method is an interactive protocol (TQA') based on teleportation. The second method is a noninteractive protocol (QA) in which the sender first encrypts the message using a protocol QEnc and then encodes the quantum ciphertext with an error correcting code chosen secretly from a set (a purity test code (PTC)). Encryption was shown to be necessary for authentication. We augment the protocol QA with an extra step which recycles the entire encryption key provided QA accepts the message. We analyze the resulting integrated protocol for quantum authentication and key generation, which we call QA+KG. Our main result is a proof that QA+KG is universal composably (UC) secure in the Ben-Or-Mayers model (quant-ph 0409062). More specifically, this implies the UC-security of (a) QA, (b) recycling of the encryption key in QA, and (c) key-recycling of the encryption scheme QEnc by appending PTC. For an m-qubit message, encryption requires 2m bits of key; but PTC can be performed using only O(log m) + O(log e) bits of key for probability of failure e. Thus, we reduce the key required for both QA and QEnc, from linear to logarithmic net consumption, at the expense of one bit of back communication which can happen any time after the conclusion of QA and before reusing the key. UC-security of QA also extends security to settings not obvious from quant-ph 0205128. Our security proof structure is inspired by and similar to that of quant-ph 0205128, reducing the security of QA to that of TQA'. In the process, we define UC-secure entanglement, and prove the UC-security of the entanglement generating protocol given in quant-ph 0205128, which could be of independent interest. Erasure coding techniques are used to increase the reliability of distributed storage systems while minimizing storage overhead. Also of interest is minimization of the bandwidth required to repair the system following a node failure. In a recent paper, characterize the tradeoff between the repair bandwidth and the amount of data stored per node. They also prove the existence of regenerating codes that achieve this tradeoff. In this paper, we introduce Exact Regenerating Codes, which are regenerating codes possessing the additional property of being able to duplicate the data stored at a failed node. Such codes require low processing and communication overheads, making the system practical and easy to maintain. Explicit construction of exact regenerating codes is provided for the minimum bandwidth point on the storage-repair bandwidth tradeoff, relevant to distributed-mail-server applications. A subspace based approach is provided and shown to yield necessary and sufficient conditions on a linear code to possess the exact regeneration property as well as prove the uniqueness of our construction. Also included in the paper, is an explicit construction of regenerating codes for the minimum storage point for parameters relevant to storage in peer-to-peer systems. This construction supports a variable number of nodes and can handle multiple, simultaneous node failures. All constructions given in the paper are of low complexity, requiring low field size in particular.