Prepare-and-Measure Certified Deletion: Difference between revisions

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<!-- Intro: brief description of the protocol -->
<!-- Intro: brief description of the protocol -->
This [https://arxiv.org/abs/1910.03551 example protocol] implements the functionality of Quantum Encryption with Certified Deletion using single-qubit state preparation and measurement.
This [https://arxiv.org/abs/1910.03551 example protocol] implements the functionality of Quantum Encryption with Certified Deletion using single-qubit state preparation and measurement. This scheme is limited to the single-use, private-key setting.
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==Assumptions==
==Requirements==
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* '''Network Stage: ''' [[:Category:Prepare and Measure Network Stage| Prepare and Measure]]


==Outline==
==Outline==
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* <math>\lambda</math>: Security parameter
* <math>\lambda</math>: Security parameter
* <math>n</math>: Length, in bits, of the message
* <math>n</math>: Length, in bits, of the message
* <math>\omega : \{0,1\} \rightarrow \mathbb{N}</math> : Hamming weight function
* <math>m = \kappa(\lambda)</math>: Total number of qubits sent from encrypting party to decrypting party
* <math>m = \kappa(\lambda)</math>: Total number of qubits sent from encrypting party to decrypting party
* <math>k</math>: Length, in bits, of the string used for verification of deletion
* <math>k</math>: Length, in bits, of the string used for verification of deletion
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==Properties==
<!-- important information on the protocol: parameters (threshold values), security claim, success probability... -->


==Protocol Description==
==Protocol Description==
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==Further Information==
==Properties==
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This scheme has the following properties:
*'''Correctness''': The scheme includes syndrome and correction functions and is thus robust against a certain amount of noise, i.e. below a certain noise threshold, the decryption circuit outputs the original message with high probability.
*'''Ciphertext Indistinguishability''': This notion implies that an adversary, given a ciphertext, cannot discern whether the original plaintext was a known message or a dummy plaintext <math>0^n</math>
*'''Certified Deletion Security''': After producing a valid deletion certificate, the adversary cannot obtain the original message, even if the key is leaked (after deletion).
==References==
* The scheme along with its formal security definitions and their proofs can be found in [https://arxiv.org/abs/1910.03551 Broadbent & Islam (2019)]


==References==
<div style='text-align: right;'>''*contributed by Chirag Wadhwa''</div>

Latest revision as of 01:25, 9 February 2022


This example protocol implements the functionality of Quantum Encryption with Certified Deletion using single-qubit state preparation and measurement. This scheme is limited to the single-use, private-key setting.

Requirements[edit]

Outline[edit]

The scheme consists of 5 circuits-

  • Key: This circuit generates the key used in later stages
  • Enc: This circuit encrypts the message using the key
  • Dec: This circuit decrypts the ciphertext using the key and generates an error flag bit
  • Del: This circuit deletes the ciphertext state and generates a deletion certificate
  • Ver: This circuit verifies the validity of the deletion certificate using the key

Notation[edit]

  • For any string and set denotes the string restricted to the bits indexed by
  • For
  • denotes the state space of a single qubit,
  • denotes the set of density operators on a Hilbert space
  • : Security parameter
  • : Length, in bits, of the message
  •  : Hamming weight function
  • : Total number of qubits sent from encrypting party to decrypting party
  • : Length, in bits, of the string used for verification of deletion
  • : Length, in bits, of the string used for extracting randomness
  • : Length, in bits, of error correction hash
  • : Length, in bits, of error syndrome
  • : Basis in which the encrypting party prepare her quantum state
  • : Threshold error rate for the verification test
  • : Set of possible bases from which \theta is chosen
  • : Universal family of hash functions used in the privacy amplification scheme
  • : Universal family of hash functions used in the error correction scheme
  • : Hash function used in the privacy amplification scheme
  • : Hash function used in the error correction scheme
  • : Function that computes the error syndrome
  • : Function that computes the corrected string

Protocol Description[edit]

Circuit 1: Key[edit]

The key generation circuit

Input : None

Output: A key state

  1. Sample
  2. Sample where
  3. Sample
  4. Sample
  5. Sample
  6. Sample
  7. Sample
  8. Output

Circuit 2: Enc[edit]

The encryption circuit

Input : A plaintext state and a key state

Output: A ciphertext state

  1. Sample where
  2. Compute where
  3. Compute
  4. Compute
  5. Output Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \rho = |r^\theta\rangle\langle r^\theta |\otimes|\mathrm{msg}\oplus x \oplus u,p,q\rangle\langle \mathrm{msg}\oplus x \oplus u,p,q |}

Circuit 3: Dec[edit]

The decryption circuit

Input : A key state Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle | r|_\tilde{\mathcal{I}},\theta,u,d,e,H_{pa},H_{ec}\rangle \langle r|_\tilde{\mathcal{I}},\theta,u,d,e,H_{pa},H_{ec}| \in \mathcal{D}(\mathcal{Q}(k+m+n+\mu+\tau)\otimes\mathfrak{H}_{pa}\otimes\mathfrak{H}_{ec}} and a ciphertext Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \rho \otimes |c,p,q\rangle\langle c,p,q| \in \mathcal{D}(\mathcal{Q}(m + n + \mu + \tau)) }

Output: A plaintext state Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \sigma \in \mathcal{D}(\mathcal{Q}(n))} and an error flag Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \gamma \in \mathcal{D}(\mathcal{Q})}

  1. Compute Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \rho^\prime = \mathrm{H}^\theta \rho \mathrm{H}^\theta}
  2. Measure Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \rho^\prime} in the computational basis. Call the result Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle r}
  3. Compute Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle r^\prime = \mathrm{corr}(r|_\mathcal{I},q\oplus e)} where Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \mathcal{I} = \{i \in [m]|\theta_i =0\}}
  4. Compute Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle p^\prime = H_{ec}(r^\prime) \oplus d }
  5. If Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle p \neq p^\prime} , then set Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \gamma = |0\rangle\langle 0|} . Else, set Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \gamma = |1\rangle\langle 1|}
  6. Compute Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle x^\prime = H_{pa}(r^\prime)}
  7. Output Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \rho \otimes \gamma = |c\oplus x^\prime \oplus u \rangle \langle c\oplus x^\prime \oplus u| \otimes \gamma }

Circuit 4: Del[edit]

The deletion circuit

Input : A ciphertext Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \rho \otimes |c,p,q\rangle\langle c,p,q| \in \mathcal{D}(\mathcal{Q}(m+n+\mu+\tau))}

Output: A certificate string Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \sigma \in \mathcal{D}(\mathcal{Q}(m))}

  1. Measure Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \rho} in the Hadamard basis. Call the output y.
  2. Output Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \sigma = |y\rangle\langle y|}

Circuit 5: Ver[edit]

The verification circuit

Input : A key state Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle | r|_\tilde{\mathcal{I}},\theta,u,d,e,H_{pa},H_{ec}\rangle \langle r|_\tilde{\mathcal{I}},\theta,u,d,e,H_{pa},H_{ec}| \in \mathcal{D}(\mathcal{Q}(k+m+n+\mu+\tau)\otimes\mathfrak{H}_{pa}\otimes\mathfrak{H}_{ec}} and a certificate string Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle |y\rangle\langle y| \in \mathcal{D}(\mathcal{Q}(m))}

Output: A bit

  1. Compute Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \hat y^\prime = \hat y|_\mathcal{\tilde{I}}} where Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \mathcal{\tilde{I}} = \{i \in [m] | \theta_i = 1 \}}
  2. Compute Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle q = r|_\tilde{\mathcal{I}}}
  3. If Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \omega(q\oplus \hat y^\prime) < k\delta} , output Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 1} . Else, output Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 0} .

Properties[edit]

This scheme has the following properties:

  • Correctness: The scheme includes syndrome and correction functions and is thus robust against a certain amount of noise, i.e. below a certain noise threshold, the decryption circuit outputs the original message with high probability.
  • Ciphertext Indistinguishability: This notion implies that an adversary, given a ciphertext, cannot discern whether the original plaintext was a known message or a dummy plaintext Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 0^n}
  • Certified Deletion Security: After producing a valid deletion certificate, the adversary cannot obtain the original message, even if the key is leaked (after deletion).

References[edit]

*contributed by Chirag Wadhwa