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In [[cryptography]], a [[cryptosystem]] is '''semantically secure''' if any [[PP (complexity)|probabilistic, polynomial-time algorithm]] (PPTA) that is given the ciphertext of a certain message <math>m</math> (taken from any distribution of messages), and the message's length, cannot determine any partial information on the message with probability [[negligible function|non-negligibly]] higher than all other PPTA's that only have access to the message length (and not the ciphertext).<ref name="goldwasser-micali 1982">[[Shafi Goldwasser|S. Goldwasser]] and [[Silvio Micali|S. Micali]], [http://portal.acm.org/citation.cfm?id=802212 Probabilistic encryption & how to play mental poker keeping secret all partial information], Annual ACM Symposium on Theory of Computing, 1982.</ref> In other words, knowledge of the ciphertext (and length) of some unknown message does not reveal any additional information on the message that can be feasibly extracted. This concept is the computational complexity analogue to [[Claude Shannon|Shannon's]] concept of [[perfect secrecy]]. Perfect secrecy means that the ciphertext reveals no information at all about the plaintext, whereas semantic security implies that any information revealed cannot be feasibly extracted<ref name="shannon">{{cite journal| last=Shannon| first=Claude| title=Communication Theory of Secrecy Systems| journal=Bell System Technical Journal| volume=28| issue=4| pages=656–715| year=1949}}</ref><ref name=Goldreich>[[Oded Goldreich|Goldreich, Oded.]] Foundations of Cryptography: Volume 2, Basic Applications. Vol. 2. Cambridge university press, 2004.</ref>{{rp|378-381}}. | |||
==History== | |||
The notion of semantic security was first put forward by [[Shafi Goldwasser|Goldwasser]] and [[Silvio Micali|Micali]] in 1982.<ref name="goldwasser-micali 1982" /> However, the definition they initially proposed offered no straightforward means to prove the security of practical cryptosystems. Goldwasser/Micali subsequently demonstrated that semantic security is equivalent to another definition of security called [[ciphertext indistinguishability]].<ref name="goldwasser-micali 1984">[[Shafi Goldwasser|S. Goldwasser]] and [[Silvio Micali|S. Micali]], [http://dx.doi.org/10.1016/0022-0000(84)90070-9 Probabilistic encryption]. Journal of Computer and System Sciences, 28:270-299, 1984.</ref> This latter definition is more common than the original definition of semantic security because it better facilitates proving the security of practical cryptosystems. | |||
==Symmetric-key cryptography== | |||
In the case of [[symmetric-key algorithm]] cryptosystems, an adversary must not be able to compute any information about a plaintext from its ciphertext. This may be posited as an adversary, given two plaintexts of equal length and their two respective ciphertexts, cannot determine which ciphertext belongs to which plaintext. | |||
==Public-key cryptography== | |||
{{Refimprove section|date=September 2012}} | |||
For an [[asymmetric key encryption algorithm]] cryptosystem to be semantically secure, it must be infeasible for a [[computational complexity|computationally bounded]] adversary to derive significant information about a message (plaintext) when given only its [[ciphertext]] and the corresponding public encryption key. Semantic security considers only the case of a "passive" attacker, i.e., one who generates and observes ciphertexts using the public key and plaintexts of her choice. Unlike other security definitions, semantic security does not consider the case of [[chosen ciphertext attack]] ([[CCA]]), where an attacker is able to request the decryption of chosen ciphertexts, and many semantically secure encryption schemes are demonstrably insecure against chosen ciphertext attack. Consequently, semantic security is now considered an insufficient condition for securing a general-purpose encryption scheme. | |||
Indistinguishability under [[chosen plaintext attack|Chosen Plaintext Attack]] ([[IND-CPA]]) is commonly defined by the following [[game]]: | |||
# A probabilistic polynomial time-bounded adversary is given a public key, which it may use to generate any number of ciphertexts (within polynomial bounds). | |||
# The adversary generates two equal-length messages <math>m_0</math> and <math>m_1</math>, and transmits them to a challenge oracle along with the public key. | |||
# The challenge oracle selects one of the messages by flipping a fair coin, encrypts the message under the public key, and returns the resulting ciphertext <math>c</math> to the adversary. | |||
The underlying [[cryptosystem]] is IND-CPA (and thus semantically secure under chosen plaintext attack) if the adversary cannot determine which of the two messages was chosen by the oracle, with probability significantly greater than <math>1/2</math> (the success rate of random guessing). Variants of this definition define indistinguishability under [[chosen ciphertext attack]] and [[adaptive chosen ciphertext attack]] ([[IND-CCA]], [[IND-CCA2]]). | |||
Because the adversary possesses the public encryption key in the above game, a semantically secure encryption scheme must by definition be [[probabilistic encryption|probabilistic]], possessing a component of [[randomness]]; if this were not the case, the adversary could simply compute the deterministic encryption of <math>m_0</math> and <math>m_1</math> and compare these encryptions with the returned ciphertext <math>c</math> to successfully guess the oracle's choice. | |||
Semantically secure encryption algorithms include [[Goldwasser-Micali cryptosystem|Goldwasser-Micali]], [[El Gamal]] and [[Paillier]]. These schemes are considered [[provable security|provably secure]], as their semantic security can be reduced to solving some hard mathematical problem (e.g., [[Decisional Diffie-Hellman assumption|Decisional Diffie-Hellman]] or the [[Quadratic Residuosity Problem]]). Other, semantically insecure algorithms such as [[RSA (algorithm)|RSA]], can be made semantically secure (under stronger assumptions) through the use of random encryption padding schemes such as [[Optimal Asymmetric Encryption Padding]] (OAEP). | |||
==References== | |||
<references /> | |||
[[Category:Theory of cryptography]] | |||
Revision as of 05:15, 4 February 2014
In cryptography, a cryptosystem is semantically secure if any probabilistic, polynomial-time algorithm (PPTA) that is given the ciphertext of a certain message (taken from any distribution of messages), and the message's length, cannot determine any partial information on the message with probability non-negligibly higher than all other PPTA's that only have access to the message length (and not the ciphertext).[1] In other words, knowledge of the ciphertext (and length) of some unknown message does not reveal any additional information on the message that can be feasibly extracted. This concept is the computational complexity analogue to Shannon's concept of perfect secrecy. Perfect secrecy means that the ciphertext reveals no information at all about the plaintext, whereas semantic security implies that any information revealed cannot be feasibly extracted[2][3]Primarily based on the most recent URA personal property value index (PPPI) flash estimates, we know that the PPPI, which represents the overall real property price development, has dipped in 2013Q4. That is the first dip the market has seen within the final 2 years.
To give you some perspective, the entire number of personal properties in Singapore (together with govt condominiums) is 297,689 in 2013Q3. Primarily based on the projection that there will be 19,302 units accomplished in 2014, the rise in residential models works out to be more than 6%. With a lot New Ec Launch Singapore provide, buyers might be spoilt for alternative and this in flip will lead to their reluctance to pay a premium for potential models. The complete textual content of the Copyright Act (Cap sixty three) and different statutes regarding IPR might be found on the Singapore Statutes Online Website online The Group's income jumped forty.1 p.c to $324.5 million from $231.6 million in FY 2013, lifted by increased development income and sales of growth properties in Singapore and China. Actual Estate Shopping for
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The story of the 23.2 home begins with a stack of Douglas fir beams salvaged from varied demolished warehouses owned by the consumer's household for a number of generations. Design and structure innovator Omer Arbel, configured them to type a triangulated roof, which makes up one of the placing features of the home. The transient from the entrepreneur-proprietor was not solely to design a house that integrates antique wood beams, however one which erases the excellence between inside and exterior. Built on a gentle slope on a large rural acreage surrounded by two masses of previous-development forests, the indoors movement seamlessly to the outdoors and, from the within looking, one enjoys unobstructed views of the existing natural panorama which is preserved
First, there are typically extra rental transactions than gross sales transactions, to permit AV to be decided for each property primarily based on comparable properties. Second, movements in sale costs are more unstable than leases. Hence, utilizing rental transactions to derive the AV helps to maintain property tax more steady for property homeowners. If you're buying or trying to lease a property. It's tiring to call up individual property agent, organize appointments, coordinate timing and to go for particular person property viewing. What most individuals do is to have a property agent representing them who will arrange and coordinate the viewings for all the properties out there based mostly on your necessities & most well-liked timing. Rent Property District 12 Rent Property District thirteen
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History
The notion of semantic security was first put forward by Goldwasser and Micali in 1982.[1] However, the definition they initially proposed offered no straightforward means to prove the security of practical cryptosystems. Goldwasser/Micali subsequently demonstrated that semantic security is equivalent to another definition of security called ciphertext indistinguishability.[4] This latter definition is more common than the original definition of semantic security because it better facilitates proving the security of practical cryptosystems.
Symmetric-key cryptography
In the case of symmetric-key algorithm cryptosystems, an adversary must not be able to compute any information about a plaintext from its ciphertext. This may be posited as an adversary, given two plaintexts of equal length and their two respective ciphertexts, cannot determine which ciphertext belongs to which plaintext.
Public-key cryptography
For an asymmetric key encryption algorithm cryptosystem to be semantically secure, it must be infeasible for a computationally bounded adversary to derive significant information about a message (plaintext) when given only its ciphertext and the corresponding public encryption key. Semantic security considers only the case of a "passive" attacker, i.e., one who generates and observes ciphertexts using the public key and plaintexts of her choice. Unlike other security definitions, semantic security does not consider the case of chosen ciphertext attack (CCA), where an attacker is able to request the decryption of chosen ciphertexts, and many semantically secure encryption schemes are demonstrably insecure against chosen ciphertext attack. Consequently, semantic security is now considered an insufficient condition for securing a general-purpose encryption scheme.
Indistinguishability under Chosen Plaintext Attack (IND-CPA) is commonly defined by the following game:
- A probabilistic polynomial time-bounded adversary is given a public key, which it may use to generate any number of ciphertexts (within polynomial bounds).
- The adversary generates two equal-length messages and , and transmits them to a challenge oracle along with the public key.
- The challenge oracle selects one of the messages by flipping a fair coin, encrypts the message under the public key, and returns the resulting ciphertext to the adversary.
The underlying cryptosystem is IND-CPA (and thus semantically secure under chosen plaintext attack) if the adversary cannot determine which of the two messages was chosen by the oracle, with probability significantly greater than (the success rate of random guessing). Variants of this definition define indistinguishability under chosen ciphertext attack and adaptive chosen ciphertext attack (IND-CCA, IND-CCA2).
Because the adversary possesses the public encryption key in the above game, a semantically secure encryption scheme must by definition be probabilistic, possessing a component of randomness; if this were not the case, the adversary could simply compute the deterministic encryption of and and compare these encryptions with the returned ciphertext to successfully guess the oracle's choice.
Semantically secure encryption algorithms include Goldwasser-Micali, El Gamal and Paillier. These schemes are considered provably secure, as their semantic security can be reduced to solving some hard mathematical problem (e.g., Decisional Diffie-Hellman or the Quadratic Residuosity Problem). Other, semantically insecure algorithms such as RSA, can be made semantically secure (under stronger assumptions) through the use of random encryption padding schemes such as Optimal Asymmetric Encryption Padding (OAEP).
References
- ↑ 1.0 1.1 S. Goldwasser and S. Micali, Probabilistic encryption & how to play mental poker keeping secret all partial information, Annual ACM Symposium on Theory of Computing, 1982.
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A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running
The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more
There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang - ↑ Goldreich, Oded. Foundations of Cryptography: Volume 2, Basic Applications. Vol. 2. Cambridge university press, 2004.
- ↑ S. Goldwasser and S. Micali, Probabilistic encryption. Journal of Computer and System Sciences, 28:270-299, 1984.