SEOUL, South Korea — The biggest political crisis for President Moon Jae-in of South Korea — weeks of large protests that have tarnished his image and forced his justice minister to resign — started with an obscure medical research paper.

The paper, published by a team of university researchers in the Korean Journal of Pathology in 2009, listed as its lead author the daughter of a professor, Cho Kuk, who would go on to become justice minister under Mr. Moon. But in August, a local newspaper revealed that the daughter’s achievement had come after only a two-week internship with the team while she was still a high school student.

The revelation infuriated South Korean students, who saw it as all the proof they needed to demand that Mr. Cho be fired, and they declared Mr. Moon’s promise to create “a world without privilege” a lie.

The scandal has exploded into the biggest embarrassment of Mr. Moon’s presidency as he has struggled with an ailing economy and a lack of opportunity for many young people. It has particularly fueled outrage about the “gold spoon” children of the elite, who glide into top-flight universities and cushy jobs, leaving their “dirt spoon” peers to struggle in South Korea’s hobbled economy.