Modeling Failure Dynamics in Time-Constrained Authentication Systems Evidence of a Success Cliff in USSD Workflows

Jul 16, 2026

Time-constrained interactive systems such as USSD-based financial services run under strict session limits and sequential user inputs. Stronger authentication improves security but adds interaction complexity and time burden, which can lower transaction completion rates. This work models failure dynamics by analyzing how authentication complexity jointly affects user response time and network round-trip time. A simulation-based framework introduces a non-linear failure phenomenon called the Success Cliff, where session success rates drop sharply after a critical complexity threshold. Controlled experiments quantify security–usability trade-offs and identify when secure workflows become operationally unreliable.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages8

Reading Time20 min

Introduction

Related Work

Authentication in USSD and Mobile Financial Systems

Limitations of Existing Approaches

Research Gap

Modeling Failure Dynamics in Time-Constrained Authentication Systems: Evidence of a Success Cliff in USSD Workflows Aklile Seyoum Mamo, Amanuel Kebede, Anny Christelle Irakoze, Jema Ndibwile∗ College of Engineering, Carnegie Mellon University Africa, Kigali, Rwanda Email: [amamo@alumni.cmu.edu](amamo@alumni.cmu.edu), [akebede@alumni.cmu.edu](akebede@alumni.cmu.edu), [cirakoze@andrew.cmu.edu](cirakoze@andrew.cmu.edu), [jndibwil@andrew.cmu.edu](jndibwil@andrew.cmu.edu) *Corresponding author arXiv :2607 .07650v 1 [ cs .CR] 8 Jul 2026 Abstract—Time-constrained interactive systems such as USSD (Unstructured Supplementary Service Data)-based financial services operate under strict session limits and sequential user interaction. While stronger authentication mechanisms improve security, they also increase interaction complexity and time burden, potentially reducing transaction completion. In this work, we model the failure dynamics of such systems and investigate how authentication complexity interacts with user response time and network round-trip time to influence session success rate. We propose and implement a simulation-based framework to investigate these failure dynamics and formally define a non-linear failure phenomenon, termed the Success Cliff, where session success rates sharply decline beyond a critical complexity threshold. Through controlled experiments, we quantify the trade-off between security and usability and identify conditions under which secure authentication workflows become operationally unreliable. I. INTRODUCTION USSD-based systems enable critical services such as mobile money, balance inquiries, and bill payments. However, USSD interactions are constrained by short session durations (typically around 120 seconds), sequential menu navigation, and reliance on user input. To enhance security, authentication mechanisms such as PIN verification, confirmation prompts, verification requiring delivery from external subsystems (e.g., SMS OTP) are commonly introduced. While these mechanisms strengthen security, they also increase interaction complexity and time requirements. This creates a fundamental challenge: secure authentication workflows may become difficult to complete within the constraints of the system. For users navigating a multi-step authentication flow under an invisible session timer [9], each additional prompt compounds cognitive load [7] and reduces the available time margin for error recovery, a dynamic that our results demonstrate can tip from manageable degradation into abrupt session failure. Despite this, existing research primarily focuses on improving authentication mechanisms rather than understanding when and why these systems fail in practice. In this paper, we move beyond system design and instead model failure dynamics in time-constrained authentication systems. We identify the Success Cliff as the point at which session completion collapses non-linearly once authentication complexity exceeds a critical threshold, and show that outof-band blocking delay, not step complexity alone, is the necessary condition for its emergence, with direct implications for authentication design in resource-constrained deployments. II. RELATED WORK A. Authentication in USSD and Mobile Financial Systems USSD-based financial systems are widely used to provide banking and mobile money services in regions with limited smartphone penetration. These systems rely on menu-driven interaction and session-based communication, requiring users to complete transactions within a fixed time window [3] . Prior work has primarily focused on strengthening authentication protocols and identifying vulnerabilities in USSD communication. For example, Lamoyero and Fajana [1] analyze USSD banking systems and show that many platforms rely on weak or single-factor authentication, making them vulnerable to attacks. Other studies propose improved authentication mechanisms, such as dynamic knowledge-based

FAQs

What problem does the paper address in USSD authentication workflows?

It addresses how strict session durations and sequential interaction constrain users, making secure authentication harder to complete and increasing session failure risk.

What is the Success Cliff phenomenon?

The Success Cliff is a non-linear point where session success rates sharply decline once authentication complexity passes a critical threshold.

How does the paper model session failure dynamics?

It proposes and implements a simulation-based framework that studies how authentication complexity interacts with user response time and network round-trip time to affect session success rate.

Jul 16, 2026

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