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Cryptographic Theory Lab
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The lab mathematically analyzes the security of cryptography and proposes new cryptosystems.
AboutAbout the lab
Verifying the security of cryptography through theory
The Cryptographic Theory Lab focuses on cryptographic theory, in particular the security analysis of cryptography.
Using mathematics and the theory of algorithms, the lab thoroughly verifies whether cryptography is truly secure.
The lab also evaluates the security of cryptography using quantum computers, and proposes cryptosystems that remain secure even after quantum computers are realized.
The lab accepts students from the College of Information Science who are working on their graduation theses.
Key terms
- Lattice reduction algorithms
- Computational methods used in the security analysis of cryptography, including the LLL algorithm.
- Shor's algorithm
- An algorithm known to be able to break RSA cryptography and elliptic curve cryptography when run on a large-scale quantum computer.
- Post-quantum cryptography
- Cryptosystems designed to remain secure even after quantum computers are realized.
NewsLab news
Lab introduction session held for third-year students of the College of Information Science (10/20)
A paper evaluating the computational complexity of Shor's algorithm was accepted to the journal IEEE Access
A paper on Shor's algorithm for the discrete logarithm problem was accepted to the journal IEEE Transactions on Quantum Engineering
A master's student received the Information Security Encouragement Award
A textbook edited by the professor, who also wrote part of it, "Ango no Riron to Gijutsu" (Theory and Technology of Cryptography), was published
ResearchResearch themes
To use cryptography with confidence, it must be thoroughly verified that it is truly secure. The lab evaluates the security of cryptosystems based on mathematical theory and the theory of algorithms, and proposes new cryptosystems.
*Illustrative imageSecurity evaluation of cryptography by lattice reduction
In RSA cryptography, a small secret key is sometimes used to speed up decryption and signature generation. The lab uses lattice reduction algorithms such as the LLL algorithm to evaluate how small the key can be made before security is compromised.
*Illustrative imageSecurity evaluation when secret keys leak
Implementation flaws and physical observation can break cryptography that is secure in theory. When an RSA secret key is obtained partially or with errors, the lab evaluates how much information is enough to compromise security, using the theory of error-correcting codes and number-theoretic algorithms, together with experiments.
*Illustrative imageSecurity evaluation using quantum computers
It is known that once large-scale quantum computers are realized, Shor's algorithm can break RSA cryptography and elliptic curve cryptography, which are widely used today. The lab designs optimal circuits for solving integer factorization and the elliptic curve discrete logarithm problem on quantum computers with many constraints, such as high noise and few qubits, aiming for a precise understanding of security.
*Illustrative imageNext-generation cryptography, including post-quantum cryptography
The lab aims to propose cryptosystems that can withstand quantum computers, so that cryptography remains secure after quantum computers are realized. Examples of next-generation cryptography include new lattice-based cryptography whose security rests on the hardness of the LWE problem and its security evaluation, code-based cryptography, and cryptography based on isogenies.
MembersFaculty
The members of the Cryptographic Theory Lab consist of a professor, researchers, and students in the doctoral program, the master's program, and the undergraduate college.As of 2026
- ProfessorNoboru Kunihiro
VoicesStudent voices
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Report an errorAbout the images
The top and research theme images are illustrative and were not taken at the lab. They are cropped from Wikimedia Commons images. Cropped CC BY-SA images are provided under the same CC BY-SA license as the original (version shown on each line).
- Top image: “RED cipher machine clutch.agr” ArnoldReinhold / CC BY-SA 4.0 (cropped)
- Security evaluation of cryptography by lattice reduction: “SIGABA-ECM (Army M-134-C, Navy CSP-888) rotors at NCM.agr” ArnoldReinhold / CC BY-SA 4.0 (cropped)
- Security evaluation when secret keys leak: “Smart-Card-Chip back” jailbird / CC BY-SA 3.0 de (cropped)
- Security evaluation using quantum computers: “Quantum Computer with Dispersive Background 2” OJB Quantum / CC BY 4.0 (cropped)
- Next-generation cryptography, including post-quantum cryptography: “Enigma Machine A16672 and relic at MIT flea.agr” ArnoldReinhold / CC BY-SA 4.0 (cropped)
- Related lab (Cryptography and Information Security Lab): “Padlock and key - 17c - Ryazan Kremlin Museum” Лапоть / CC0 (cropped)
- Related lab (Quantum Computation Theory Lab): “Cat Qubit Boson Chip” SachaAB / CC BY 4.0 (cropped)
- Related lab (Theoretical Computer Science Lab (Masayuki Miyamoto)): “IBM Q system (Fraunhofer 2)” IBM Research / CC BY 2.0 (cropped)
- Related lab (System Security Lab): “LC-P computer keyboard - IC encapsulated on printed circuit board-3464” Raimond Spekking / CC BY-SA 4.0 (cropped)
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