Posts Tagged ‘Cryptography’

Elonka Dunin and Klaus Schmeh, renowned cryptology experts, unravel the mystery of encrypted advertisements published in The Times between 1850 and 1855. Intended for Captain Richard Collinson during his Arctic expedition, these ads used a modified Royal Navy signal-book cipher. Elonka and Klaus’s presentation traces their efforts to decrypt all ads, providing historical and cryptographic insights into a unique communication system.

The Collinson Cipher System

Elonka introduces the encrypted ads, designed to keep Collinson informed of family matters during his search for the lost Franklin expedition. The cipher, based on a Royal Navy signal-book, allowed Collinson’s family to encode messages for publication in The Times, accessible globally. Elonka’s narrative highlights the system’s ingenuity, enabling secure communication in an era of limited technology.

Decrypting Historical Messages

Klaus details their decryption process, building on 1990s efforts to break the cipher. Using their expertise, documented in their book from No Starch Press, Klaus and Elonka decoded over 50 ads, placing them in geographic and cultural context. Their work reveals personal details, such as messages from Collinson’s sister Julia, showcasing the cipher’s effectiveness despite logistical challenges.

Challenges and Limitations

The duo discusses the system’s mixed success, noting that Collinson received only four messages in Banuwangi due to expedition unrest. Klaus addresses the cipher’s vulnerabilities, such as predictable patterns, which modern techniques could exploit. Their analysis, enriched by historical records, underscores the challenges of maintaining secure communication in remote settings.

Modern Cryptographic Relevance

Concluding, Elonka explores the potential of artificial intelligence in cryptanalysis, noting that LLMs struggle with precise tasks like counting letters but excel in pattern recognition. Their work invites further research into historical ciphers, inspiring cryptographers to apply modern tools to uncover past secrets, preserving the legacy of Collinson’s innovative system.

Links:

• Elonka Dunin on LinkedIn
• No Starch Press website

Do You Really Know JWT? Insights from Devoxx France 2022

Karim Pinchon, a backend developer at Ornikar, delivered an illuminating talk titled “Do You Really Know JWT?” (watch on YouTube). With a decade of experience across Java, PHP, and Go, Karim dives into JSON Web Tokens (JWT), a standard for secure data transfer in authentication and authorization. This session explores JWT’s structure, cryptographic foundations, vulnerabilities, and best practices, moving beyond common usage in OAuth2 and OpenID Connect.

Understanding JWT Structure and Cryptography

Karim begins by demystifying JWT, a compact, secure token for transferring JSON data, often used in HTTP headers for authentication. A JWT comprises three parts—header, payload, and signature—encoded in Base64 and concatenated with dots. The header specifies the cryptographic algorithm (e.g., HMAC, RSA), the payload contains claims (data), and the signature ensures integrity. Karim demonstrates this using jwt.io, showing how decoding reveals JSON objects.

He distinguishes token types: reference tokens (database-backed) and value tokens (self-contained, like JWT). JWT supports two forms: compact (Base64-encoded) and JSON (with additional features like multiple signatures). Karim introduces related standards under JOSE (JSON Object Signing and Encryption), including JWS (signed tokens), JWE (encrypted tokens), JWK (key management), and JWA (algorithms). Cryptographic operations like signing (for integrity) and encryption (for confidentiality) underpin JWT’s security.

Payload Claims and Use Cases

The payload is JWT’s core, divided into three claim types:

• Registered Claims: Standard fields like issuer (iss), audience (aud), expiration (exp), and token ID (jti) for validation.
• Public Claims: Defined by IANA for protocols like OpenID Connect, carrying user data (e.g., name, email) in ID tokens.
• Private Claims: Custom data agreed upon by parties, kept minimal for compactness.

Karim highlights JWT’s versatility in:

• API Authentication: Tokens in Authorization headers validate requests without database lookups.
• OAuth2: Access tokens may be JWTs, carrying authorization data.
• OpenID Connect: ID tokens propagate user identity.
• Stateless Sessions: Storing session data (e.g., e-commerce carts) client-side, enhancing scalability.

He cautions that stateless sessions require careful implementation to avoid complexity.

Security Vulnerabilities and Attacks

Karim dedicates significant time to JWT’s security risks, demonstrating attacks via a PHP library on his GitHub. Common vulnerabilities include:

• Unsecured Tokens: Setting the header’s algorithm to none bypasses signature verification, a flaw exploited in some libraries. Karim shows a test where a modified token passes validation due to this.
• RSA Public Key as Shared Key: An attacker changes the algorithm from RSA to HMAC, using the public key as a shared secret, tricking servers into validating tampered tokens.
• Brute Force: Weak secrets (e.g., “azerty”) are vulnerable to brute-force attacks.
• Encrypted Data Modification: Some encryption algorithms allow payload tampering (e.g., flipping is_admin from false to true) without breaking the cipher.
• Token Substitution: Using a token from one service (where the user is admin) on another without proper audience validation.

Karim emphasizes the JWT paradox: the header, which specifies validation details, can’t be trusted until the token is validated. He attributes these issues to developers’ reliance on unvetted libraries, not poor coding.

Best Practices for Secure JWT Usage

To mitigate risks, Karim offers practical advice:

• Protect Secrets: Use strong, rotated keys. Avoid sharing symmetric keys with external partners; prefer asymmetric keys (e.g., RSA).
• Restrict Algorithms: Servers should only accept predefined algorithms (e.g., one or two), ignoring the header’s alg field.
• Validate Claims: Check iss, aud, and exp to ensure the token’s legitimacy. Reject tokens not intended for your service.
• Use Trusted Libraries: Avoid custom implementations. Modern libraries require explicit algorithm whitelists, reducing none algorithm risks.
• Short Token Lifespans: Minimize revocation needs with short-lived tokens. Avoid external revocation lists, as they undermine JWT’s autonomy.
• Ensure Confidentiality: Since JWS payloads are Base64-encoded (readable), avoid sensitive data. Use JWE for encryption if needed, and transmit over HTTPS.

Karim also mentions alternatives like Biscuits (from Clever Cloud), PASETO, and Google’s Macaroons, which address JWT’s flaws, such as untrusted headers.

Links

• YouTube Video: Do You Really Know JWT?
• Karim Pinchon: LinkedIn, Twitter, GitHub
• Ornikar: Official Website
• JWT: Official Website

Hashtags: #DevoxxFrance #KarimPinchon #JWT #Security #Cryptography #Authentication #Authorization #OAuth2 #OpenIDConnect #JWS #JWE #JWK #Ornikar #PHP #Java

In realms where randomness reigns—visas’ vagaries, audits’ allocations, tournaments’ tabulations—authorities’ assertions of equity often echo empty, bereft of corroboration. Joseph Bonneau, a cryptographer and researcher at Stanford’s Applied Crypto Group, demystified this domain at dotSecurity 2017, championing verifiable randomness as algorithmic accountability’s anchor. Formerly of Google and the Electronic Frontier Foundation, Joseph’s journey—Bitcoin’s blockchain to privacy’s precincts—culminates in constructs that compel proof from the capricious, from dice’s clatter to cryptographic commitments.

Joseph’s journey juxtaposed physical proofs’ pitfalls: lottery balls’ bias, dice’s deceit—transparency’s theater, yet tampering’s temptation. Cryptography’s counter: commitments’ covenant—hash’s hideaway, revealing randomness post-participation. Verifiable delay functions (VDFs) vex velocity: computations’ chronology, proofs’ promptness—adversaries’ acceleration averted. Joseph’s jewel: lottery’s ledger—participants’ pledges, commitments’ concatenation, hash’s harvest yielding winners’ wreath.

Applications amplify: H1B visas’ vagaries verified, elections’ audits authenticated—overbooked flights’ farewells fair. Joseph’s jibe: FIFA’s football fiascoes, fans’ fury—verifiability’s vindication. Blockchain’s boon: Bitcoin’s beacons, stock quotes’ surrogates—delay’s defense against traders’ tempo.

Challenges chime: VDFs’ verification velocity, parallelism’s peril—research’s realm ripe. Joseph’s rallying cry: demand documentation—dashlane’s draws, FIFA’s fixtures, governments’ gambits—cryptography’s capability calls.

Randomness’ Riddles and Physical Pitfalls

Joseph juxtaposed balls’ bias, dice’s deceit—commitments’ cure, delay’s deterrent.

Constructs’ Craft and Applications’ Ambit

Hash’s haven, VDFs’ vigil—lotteries’ ledger, visas’ verity. Blockchain’s bastion, stocks’ surrogate.

Links:

• Joseph Bonneau on LinkedIn
• Stanford University

In the shadowed corridors of computational evolution, where qubits dance on the precipice of unraveling classical safeguards, the specter of quantum supremacy looms as both marvel and menace. Tanja Lange, a pioneering cryptographer and chair of the Coding Theory and Cryptology group at Eindhoven University of Technology, confronted this conundrum at dotSecurity 2017, elucidating the imperative for encryption resilient to tomorrow’s quantum tempests. With a career illuminating the interstices of mathematics and machine security, Tanja dissected the vulnerabilities plaguing contemporary ciphers—RSA’s reliance on factorization’s fortress, ECC’s elliptic enigmas—while heralding lattice-based bastions and code-theoretic countermeasures as beacons of post-quantum fortitude. This discourse transcends abstraction; it charts a course for safeguarding secrets sown today from harvests reaped by adversaries armed with tomorrow’s arithmetic.

Tanja’s treatise commenced with cryptography’s ubiquity: the browser’s lock icon, a talisman of TLS’s aegis, enshrines RSA or Diffie-Hellman duos, their potency predicated on problems polynomials presume intractable. Yet, Shor’s quantum sleight—factoring in factorial fractions, discrete logs dispatched—threatens this tranquility. Grover’s oracle amplifies: symmetric keys halved in fortitude, AES-256’s bulwark bruised to 128-bit equivalence. Retroactive peril compounds: “harvest now, decrypt later,” state actors stockpiling streams for quantum quelling. Tanja tallied timelines: Google’s Sycamore’s supremacy in 2019, IBM’s 2023 roadmap to 1,000+ qubits—2025’s horizon harbors harbingers capable of cracking 2048-bit RSA in hours.

Post-quantum’s pantheon pivots on presumptions quantum-proof: lattices’ learning with errors (LWE), multivariate quadratics’ mazes, hash’s hierarchies. Tanja traversed LWE’s labyrinth: vectors veiled in noise, decoding’s dichotomy—structured sparsity succumbing sans trapdoors, randomness repelling revelation. McEliece’s mantle, code-based cryptography’s cornerstone since 1978, endures: Goppa codes’ generator matrices, encryption as error-infused syndromes—decryption’s discernment demands secret scaffolds. Tanja touted standardization’s sprint: NIST’s 2016 clarion, 2022’s Kyber crystallization (lattice largesse), Dilithium’s digital signatures—round three’s rites refining resilience.

Challenges cascade: key sizes’ kilobyte burdens (Kyber’s 1KB public, McEliece’s megabyte monoliths), signatures’ sprawl—yet optimizations orbit: hybrid harbingers blending classical clutches with quantum cautions. Tanja tempered trepidation: current crypto’s continuum, migration’s mosaic—signal spikes, certificate cascades. Her horizon: PQC’s proliferation, from Chrome’s 2024 infusions to IETF’s interoperability—ensuring enclaves eternal against entanglement’s edge.

Quantum’s Quandary and Classical Cracks

Tanja traced threats: Shor’s sieve shattering RSA’s ramparts, Grover’s grope gnawing symmetric sinews—harvest’s haunt, 2025’s qubit quorum. ECC’s edifice echoes: elliptic’s enigmas eclipsed, Diffie-Hellman’s duels dissolved.

Lattice Locks and Code Crypts

LWE’s veil: noise’s nebula, trapdoors’ trove—McEliece’s matrices, Goppa’s girth. NIST’s novelties: Kyber’s kernels, Dilithium’s declarations—hybrids’ harmony, keys’ curtailment.

Migration’s Mandate and Horizons

Tanja’s timeline: signal’s surge, certs’ cascade—Chrome’s convergence, IETF’s accord. PQC’s promise: enclaves enduring, entanglement evaded.

Links:

• Tanja Lange on Google Scholar
• Eindhoven University of Technology