How HOTP (RFC 4226) turns a shared secret and a counter into a 6-digit one-time password using HMAC-SHA-1 and dynamic truncation, with its security analysis, validation rules, and link to TOTP.
2026, Jul 20 — 16 minute read
A formal walkthrough of the Brewer and Nash Chinese Wall security policy, its conflict-of-interest access rules, its *-property against indirect flows, and why it cannot be reduced to Bell-LaPadula.
2026, Jul 20 — 15 minute read
A technical walkthrough of the 1973 Black-Scholes paper - the no-arbitrage hedging argument, the option pricing differential equation, its closed-form solution, and the reading of corporate liabilities as options.
2026, Jul 18 — 21 minute read
A simple guide to the Black-Scholes model - what an option is, why pricing it was a hard puzzle, and how two clever people solved it, explained with everyday analogies for curious readers.
2026, Jul 18 — 12 minute read
How ISO 20022 models bank guarantees and standby letters of credit through the tsrv business area, covering the issuance, amendment, demand, and termination of an undertaking between applicant, guarantor, advising party, and beneficiary.
2026, Jul 17 — 8 minute read
How ISO 20022 modelled the Bank Payment Obligation and the Trade Services Utility through the tsmt business area, covering the baseline, data set matching, status management, and reporting that drive a conditional interbank payment obligation.
2026, Jul 17 — 8 minute read
How ISO 20022 models the corporate-to-bank front end of trade finance through the tsin business area, covering invoice financing, invoice assignment for factoring, party registration and guarantee, and undertaking applications.
2026, Jul 17 — 7 minute read
